FreeBSD/Linux Kernel Cross Reference
sys/mm/mmap.c

     /*
      * mm/mmap.c
      *
      * Written by obz.
      *
      * Address space accounting code        <alan@lxorguk.ukuu.org.uk>
      */
     
     #include <linux/slab.h>
    #include <linux/backing-dev.h>
    #include <linux/mm.h>
    #include <linux/shm.h>
    #include <linux/mman.h>
    #include <linux/pagemap.h>
    #include <linux/swap.h>
    #include <linux/syscalls.h>
    #include <linux/capability.h>
    #include <linux/init.h>
    #include <linux/file.h>
    #include <linux/fs.h>
    #include <linux/personality.h>
    #include <linux/security.h>
    #include <linux/hugetlb.h>
    #include <linux/profile.h>
    #include <linux/export.h>
    #include <linux/mount.h>
    #include <linux/mempolicy.h>
    #include <linux/rmap.h>
    #include <linux/mmu_notifier.h>
    #include <linux/perf_event.h>
    #include <linux/audit.h>
    #include <linux/khugepaged.h>
    #include <linux/uprobes.h>
    #include <linux/rbtree_augmented.h>
    
    #include <asm/uaccess.h>
    #include <asm/cacheflush.h>
    #include <asm/tlb.h>
    #include <asm/mmu_context.h>
    
    #include "internal.h"
    
    #ifndef arch_mmap_check
    #define arch_mmap_check(addr, len, flags)       (0)
    #endif
    
    #ifndef arch_rebalance_pgtables
    #define arch_rebalance_pgtables(addr, len)              (addr)
    #endif
    
    static void unmap_region(struct mm_struct *mm,
                    struct vm_area_struct *vma, struct vm_area_struct *prev,
                    unsigned long start, unsigned long end);
    
    /* description of effects of mapping type and prot in current implementation.
     * this is due to the limited x86 page protection hardware.  The expected
     * behavior is in parens:
     *
     * map_type     prot
     *              PROT_NONE       PROT_READ       PROT_WRITE      PROT_EXEC
     * MAP_SHARED   r: (no) no      r: (yes) yes    r: (no) yes     r: (no) yes
     *              w: (no) no      w: (no) no      w: (yes) yes    w: (no) no
     *              x: (no) no      x: (no) yes     x: (no) yes     x: (yes) yes
     *              
     * MAP_PRIVATE  r: (no) no      r: (yes) yes    r: (no) yes     r: (no) yes
     *              w: (no) no      w: (no) no      w: (copy) copy  w: (no) no
     *              x: (no) no      x: (no) yes     x: (no) yes     x: (yes) yes
     *
     */
    pgprot_t protection_map[16] = {
            __P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
            __S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
    };
    
    pgprot_t vm_get_page_prot(unsigned long vm_flags)
    {
            return __pgprot(pgprot_val(protection_map[vm_flags &
                                    (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
                            pgprot_val(arch_vm_get_page_prot(vm_flags)));
    }
    EXPORT_SYMBOL(vm_get_page_prot);
    
    int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;  /* heuristic overcommit */
    int sysctl_overcommit_ratio __read_mostly = 50; /* default is 50% */
    int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
    /*
     * Make sure vm_committed_as in one cacheline and not cacheline shared with
     * other variables. It can be updated by several CPUs frequently.
     */
    struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp;
    
    /*
     * The global memory commitment made in the system can be a metric
     * that can be used to drive ballooning decisions when Linux is hosted
     * as a guest. On Hyper-V, the host implements a policy engine for dynamically
     * balancing memory across competing virtual machines that are hosted.
     * Several metrics drive this policy engine including the guest reported
     * memory commitment.
     */
   unsigned long vm_memory_committed(void)
   {
           return percpu_counter_read_positive(&vm_committed_as);
   }
   EXPORT_SYMBOL_GPL(vm_memory_committed);
   
   /*
    * Check that a process has enough memory to allocate a new virtual
    * mapping. 0 means there is enough memory for the allocation to
    * succeed and -ENOMEM implies there is not.
    *
    * We currently support three overcommit policies, which are set via the
    * vm.overcommit_memory sysctl.  See Documentation/vm/overcommit-accounting
    *
    * Strict overcommit modes added 2002 Feb 26 by Alan Cox.
    * Additional code 2002 Jul 20 by Robert Love.
    *
    * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise.
    *
    * Note this is a helper function intended to be used by LSMs which
    * wish to use this logic.
    */
   int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
   {
           unsigned long free, allowed;
   
           vm_acct_memory(pages);
   
           /*
            * Sometimes we want to use more memory than we have
            */
           if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
                   return 0;
   
           if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {
                   free = global_page_state(NR_FREE_PAGES);
                   free += global_page_state(NR_FILE_PAGES);
   
                   /*
                    * shmem pages shouldn't be counted as free in this
                    * case, they can't be purged, only swapped out, and
                    * that won't affect the overall amount of available
                    * memory in the system.
                    */
                   free -= global_page_state(NR_SHMEM);
   
                   free += nr_swap_pages;
   
                   /*
                    * Any slabs which are created with the
                    * SLAB_RECLAIM_ACCOUNT flag claim to have contents
                    * which are reclaimable, under pressure.  The dentry
                    * cache and most inode caches should fall into this
                    */
                   free += global_page_state(NR_SLAB_RECLAIMABLE);
   
                   /*
                    * Leave reserved pages. The pages are not for anonymous pages.
                    */
                   if (free <= totalreserve_pages)
                           goto error;
                   else
                           free -= totalreserve_pages;
   
                   /*
                    * Leave the last 3% for root
                    */
                   if (!cap_sys_admin)
                           free -= free / 32;
   
                   if (free > pages)
                           return 0;
   
                   goto error;
           }
   
           allowed = (totalram_pages - hugetlb_total_pages())
                   * sysctl_overcommit_ratio / 100;
           /*
            * Leave the last 3% for root
            */
           if (!cap_sys_admin)
                   allowed -= allowed / 32;
           allowed += total_swap_pages;
   
           /* Don't let a single process grow too big:
              leave 3% of the size of this process for other processes */
           if (mm)
                   allowed -= mm->total_vm / 32;
   
           if (percpu_counter_read_positive(&vm_committed_as) < allowed)
                   return 0;
   error:
           vm_unacct_memory(pages);
   
           return -ENOMEM;
   }
   
   /*
    * Requires inode->i_mapping->i_mmap_mutex
    */
   static void __remove_shared_vm_struct(struct vm_area_struct *vma,
                   struct file *file, struct address_space *mapping)
   {
           if (vma->vm_flags & VM_DENYWRITE)
                   atomic_inc(&file->f_path.dentry->d_inode->i_writecount);
           if (vma->vm_flags & VM_SHARED)
                   mapping->i_mmap_writable--;
   
           flush_dcache_mmap_lock(mapping);
           if (unlikely(vma->vm_flags & VM_NONLINEAR))
                   list_del_init(&vma->shared.nonlinear);
           else
                   vma_interval_tree_remove(vma, &mapping->i_mmap);
           flush_dcache_mmap_unlock(mapping);
   }
   
   /*
    * Unlink a file-based vm structure from its interval tree, to hide
    * vma from rmap and vmtruncate before freeing its page tables.
    */
   void unlink_file_vma(struct vm_area_struct *vma)
   {
           struct file *file = vma->vm_file;
   
           if (file) {
                   struct address_space *mapping = file->f_mapping;
                   mutex_lock(&mapping->i_mmap_mutex);
                   __remove_shared_vm_struct(vma, file, mapping);
                   mutex_unlock(&mapping->i_mmap_mutex);
           }
   }
   
   /*
    * Close a vm structure and free it, returning the next.
    */
   static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
   {
           struct vm_area_struct *next = vma->vm_next;
   
           might_sleep();
           if (vma->vm_ops && vma->vm_ops->close)
                   vma->vm_ops->close(vma);
           if (vma->vm_file)
                   fput(vma->vm_file);
           mpol_put(vma_policy(vma));
           kmem_cache_free(vm_area_cachep, vma);
           return next;
   }
   
   static unsigned long do_brk(unsigned long addr, unsigned long len);
   
   SYSCALL_DEFINE1(brk, unsigned long, brk)
   {
           unsigned long rlim, retval;
           unsigned long newbrk, oldbrk;
           struct mm_struct *mm = current->mm;
           unsigned long min_brk;
   
           down_write(&mm->mmap_sem);
   
   #ifdef CONFIG_COMPAT_BRK
           /*
            * CONFIG_COMPAT_BRK can still be overridden by setting
            * randomize_va_space to 2, which will still cause mm->start_brk
            * to be arbitrarily shifted
            */
           if (current->brk_randomized)
                   min_brk = mm->start_brk;
           else
                   min_brk = mm->end_data;
   #else
           min_brk = mm->start_brk;
   #endif
           if (brk < min_brk)
                   goto out;
   
           /*
            * Check against rlimit here. If this check is done later after the test
            * of oldbrk with newbrk then it can escape the test and let the data
            * segment grow beyond its set limit the in case where the limit is
            * not page aligned -Ram Gupta
            */
           rlim = rlimit(RLIMIT_DATA);
           if (rlim < RLIM_INFINITY && (brk - mm->start_brk) +
                           (mm->end_data - mm->start_data) > rlim)
                   goto out;
   
           newbrk = PAGE_ALIGN(brk);
           oldbrk = PAGE_ALIGN(mm->brk);
           if (oldbrk == newbrk)
                   goto set_brk;
   
           /* Always allow shrinking brk. */
           if (brk <= mm->brk) {
                   if (!do_munmap(mm, newbrk, oldbrk-newbrk))
                           goto set_brk;
                   goto out;
           }
   
           /* Check against existing mmap mappings. */
           if (find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE))
                   goto out;
   
           /* Ok, looks good - let it rip. */
           if (do_brk(oldbrk, newbrk-oldbrk) != oldbrk)
                   goto out;
   set_brk:
           mm->brk = brk;
   out:
           retval = mm->brk;
           up_write(&mm->mmap_sem);
           return retval;
   }
   
   static long vma_compute_subtree_gap(struct vm_area_struct *vma)
   {
           unsigned long max, subtree_gap;
           max = vma->vm_start;
           if (vma->vm_prev)
                   max -= vma->vm_prev->vm_end;
           if (vma->vm_rb.rb_left) {
                   subtree_gap = rb_entry(vma->vm_rb.rb_left,
                                   struct vm_area_struct, vm_rb)->rb_subtree_gap;
                   if (subtree_gap > max)
                           max = subtree_gap;
           }
           if (vma->vm_rb.rb_right) {
                   subtree_gap = rb_entry(vma->vm_rb.rb_right,
                                   struct vm_area_struct, vm_rb)->rb_subtree_gap;
                   if (subtree_gap > max)
                           max = subtree_gap;
           }
           return max;
   }
   
   #ifdef CONFIG_DEBUG_VM_RB
   static int browse_rb(struct rb_root *root)
   {
           int i = 0, j, bug = 0;
           struct rb_node *nd, *pn = NULL;
           unsigned long prev = 0, pend = 0;
   
           for (nd = rb_first(root); nd; nd = rb_next(nd)) {
                   struct vm_area_struct *vma;
                   vma = rb_entry(nd, struct vm_area_struct, vm_rb);
                   if (vma->vm_start < prev) {
                           printk("vm_start %lx prev %lx\n", vma->vm_start, prev);
                           bug = 1;
                   }
                   if (vma->vm_start < pend) {
                           printk("vm_start %lx pend %lx\n", vma->vm_start, pend);
                           bug = 1;
                   }
                   if (vma->vm_start > vma->vm_end) {
                           printk("vm_end %lx < vm_start %lx\n",
                                   vma->vm_end, vma->vm_start);
                           bug = 1;
                   }
                   if (vma->rb_subtree_gap != vma_compute_subtree_gap(vma)) {
                           printk("free gap %lx, correct %lx\n",
                                  vma->rb_subtree_gap,
                                  vma_compute_subtree_gap(vma));
                           bug = 1;
                   }
                   i++;
                   pn = nd;
                   prev = vma->vm_start;
                   pend = vma->vm_end;
           }
           j = 0;
           for (nd = pn; nd; nd = rb_prev(nd))
                   j++;
           if (i != j) {
                   printk("backwards %d, forwards %d\n", j, i);
                   bug = 1;
           }
           return bug ? -1 : i;
   }
   
   static void validate_mm_rb(struct rb_root *root, struct vm_area_struct *ignore)
   {
           struct rb_node *nd;
   
           for (nd = rb_first(root); nd; nd = rb_next(nd)) {
                   struct vm_area_struct *vma;
                   vma = rb_entry(nd, struct vm_area_struct, vm_rb);
                   BUG_ON(vma != ignore &&
                          vma->rb_subtree_gap != vma_compute_subtree_gap(vma));
           }
   }
   
   void validate_mm(struct mm_struct *mm)
   {
           int bug = 0;
           int i = 0;
           unsigned long highest_address = 0;
           struct vm_area_struct *vma = mm->mmap;
           while (vma) {
                   struct anon_vma_chain *avc;
                   vma_lock_anon_vma(vma);
                   list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                           anon_vma_interval_tree_verify(avc);
                   vma_unlock_anon_vma(vma);
                   highest_address = vma->vm_end;
                   vma = vma->vm_next;
                   i++;
           }
           if (i != mm->map_count) {
                   printk("map_count %d vm_next %d\n", mm->map_count, i);
                   bug = 1;
           }
           if (highest_address != mm->highest_vm_end) {
                   printk("mm->highest_vm_end %lx, found %lx\n",
                          mm->highest_vm_end, highest_address);
                   bug = 1;
           }
           i = browse_rb(&mm->mm_rb);
           if (i != mm->map_count) {
                   printk("map_count %d rb %d\n", mm->map_count, i);
                   bug = 1;
           }
           BUG_ON(bug);
   }
   #else
   #define validate_mm_rb(root, ignore) do { } while (0)
   #define validate_mm(mm) do { } while (0)
   #endif
   
   RB_DECLARE_CALLBACKS(static, vma_gap_callbacks, struct vm_area_struct, vm_rb,
                        unsigned long, rb_subtree_gap, vma_compute_subtree_gap)
   
   /*
    * Update augmented rbtree rb_subtree_gap values after vma->vm_start or
    * vma->vm_prev->vm_end values changed, without modifying the vma's position
    * in the rbtree.
    */
   static void vma_gap_update(struct vm_area_struct *vma)
   {
           /*
            * As it turns out, RB_DECLARE_CALLBACKS() already created a callback
            * function that does exacltly what we want.
            */
           vma_gap_callbacks_propagate(&vma->vm_rb, NULL);
   }
   
   static inline void vma_rb_insert(struct vm_area_struct *vma,
                                    struct rb_root *root)
   {
           /* All rb_subtree_gap values must be consistent prior to insertion */
           validate_mm_rb(root, NULL);
   
           rb_insert_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
   }
   
   static void vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
   {
           /*
            * All rb_subtree_gap values must be consistent prior to erase,
            * with the possible exception of the vma being erased.
            */
           validate_mm_rb(root, vma);
   
           /*
            * Note rb_erase_augmented is a fairly large inline function,
            * so make sure we instantiate it only once with our desired
            * augmented rbtree callbacks.
            */
           rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
   }
   
   /*
    * vma has some anon_vma assigned, and is already inserted on that
    * anon_vma's interval trees.
    *
    * Before updating the vma's vm_start / vm_end / vm_pgoff fields, the
    * vma must be removed from the anon_vma's interval trees using
    * anon_vma_interval_tree_pre_update_vma().
    *
    * After the update, the vma will be reinserted using
    * anon_vma_interval_tree_post_update_vma().
    *
    * The entire update must be protected by exclusive mmap_sem and by
    * the root anon_vma's mutex.
    */
   static inline void
   anon_vma_interval_tree_pre_update_vma(struct vm_area_struct *vma)
   {
           struct anon_vma_chain *avc;
   
           list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                   anon_vma_interval_tree_remove(avc, &avc->anon_vma->rb_root);
   }
   
   static inline void
   anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
   {
           struct anon_vma_chain *avc;
   
           list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                   anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root);
   }
   
   static int find_vma_links(struct mm_struct *mm, unsigned long addr,
                   unsigned long end, struct vm_area_struct **pprev,
                   struct rb_node ***rb_link, struct rb_node **rb_parent)
   {
           struct rb_node **__rb_link, *__rb_parent, *rb_prev;
   
           __rb_link = &mm->mm_rb.rb_node;
           rb_prev = __rb_parent = NULL;
   
           while (*__rb_link) {
                   struct vm_area_struct *vma_tmp;
   
                   __rb_parent = *__rb_link;
                   vma_tmp = rb_entry(__rb_parent, struct vm_area_struct, vm_rb);
   
                   if (vma_tmp->vm_end > addr) {
                           /* Fail if an existing vma overlaps the area */
                           if (vma_tmp->vm_start < end)
                                   return -ENOMEM;
                           __rb_link = &__rb_parent->rb_left;
                   } else {
                           rb_prev = __rb_parent;
                           __rb_link = &__rb_parent->rb_right;
                   }
           }
   
           *pprev = NULL;
           if (rb_prev)
                   *pprev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
           *rb_link = __rb_link;
           *rb_parent = __rb_parent;
           return 0;
   }
   
   void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
                   struct rb_node **rb_link, struct rb_node *rb_parent)
   {
           /* Update tracking information for the gap following the new vma. */
           if (vma->vm_next)
                   vma_gap_update(vma->vm_next);
           else
                   mm->highest_vm_end = vma->vm_end;
   
           /*
            * vma->vm_prev wasn't known when we followed the rbtree to find the
            * correct insertion point for that vma. As a result, we could not
            * update the vma vm_rb parents rb_subtree_gap values on the way down.
            * So, we first insert the vma with a zero rb_subtree_gap value
            * (to be consistent with what we did on the way down), and then
            * immediately update the gap to the correct value. Finally we
            * rebalance the rbtree after all augmented values have been set.
            */
           rb_link_node(&vma->vm_rb, rb_parent, rb_link);
           vma->rb_subtree_gap = 0;
           vma_gap_update(vma);
           vma_rb_insert(vma, &mm->mm_rb);
   }
   
   static void __vma_link_file(struct vm_area_struct *vma)
   {
           struct file *file;
   
           file = vma->vm_file;
           if (file) {
                   struct address_space *mapping = file->f_mapping;
   
                   if (vma->vm_flags & VM_DENYWRITE)
                           atomic_dec(&file->f_path.dentry->d_inode->i_writecount);
                   if (vma->vm_flags & VM_SHARED)
                           mapping->i_mmap_writable++;
   
                   flush_dcache_mmap_lock(mapping);
                   if (unlikely(vma->vm_flags & VM_NONLINEAR))
                           vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
                   else
                           vma_interval_tree_insert(vma, &mapping->i_mmap);
                   flush_dcache_mmap_unlock(mapping);
           }
   }
   
   static void
   __vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
           struct vm_area_struct *prev, struct rb_node **rb_link,
           struct rb_node *rb_parent)
   {
           __vma_link_list(mm, vma, prev, rb_parent);
           __vma_link_rb(mm, vma, rb_link, rb_parent);
   }
   
   static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
                           struct vm_area_struct *prev, struct rb_node **rb_link,
                           struct rb_node *rb_parent)
   {
           struct address_space *mapping = NULL;
   
           if (vma->vm_file)
                   mapping = vma->vm_file->f_mapping;
   
           if (mapping)
                   mutex_lock(&mapping->i_mmap_mutex);
   
           __vma_link(mm, vma, prev, rb_link, rb_parent);
           __vma_link_file(vma);
   
           if (mapping)
                   mutex_unlock(&mapping->i_mmap_mutex);
   
           mm->map_count++;
           validate_mm(mm);
   }
   
   /*
    * Helper for vma_adjust() in the split_vma insert case: insert a vma into the
    * mm's list and rbtree.  It has already been inserted into the interval tree.
    */
   static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
   {
           struct vm_area_struct *prev;
           struct rb_node **rb_link, *rb_parent;
   
           if (find_vma_links(mm, vma->vm_start, vma->vm_end,
                              &prev, &rb_link, &rb_parent))
                   BUG();
           __vma_link(mm, vma, prev, rb_link, rb_parent);
           mm->map_count++;
   }
   
   static inline void
   __vma_unlink(struct mm_struct *mm, struct vm_area_struct *vma,
                   struct vm_area_struct *prev)
   {
           struct vm_area_struct *next;
   
           vma_rb_erase(vma, &mm->mm_rb);
           prev->vm_next = next = vma->vm_next;
           if (next)
                   next->vm_prev = prev;
           if (mm->mmap_cache == vma)
                   mm->mmap_cache = prev;
   }
   
   /*
    * We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
    * is already present in an i_mmap tree without adjusting the tree.
    * The following helper function should be used when such adjustments
    * are necessary.  The "insert" vma (if any) is to be inserted
    * before we drop the necessary locks.
    */
   int vma_adjust(struct vm_area_struct *vma, unsigned long start,
           unsigned long end, pgoff_t pgoff, struct vm_area_struct *insert)
   {
           struct mm_struct *mm = vma->vm_mm;
           struct vm_area_struct *next = vma->vm_next;
           struct vm_area_struct *importer = NULL;
           struct address_space *mapping = NULL;
           struct rb_root *root = NULL;
           struct anon_vma *anon_vma = NULL;
           struct file *file = vma->vm_file;
           bool start_changed = false, end_changed = false;
           long adjust_next = 0;
           int remove_next = 0;
   
           if (next && !insert) {
                   struct vm_area_struct *exporter = NULL;
   
                   if (end >= next->vm_end) {
                           /*
                            * vma expands, overlapping all the next, and
                            * perhaps the one after too (mprotect case 6).
                            */
   again:                  remove_next = 1 + (end > next->vm_end);
                           end = next->vm_end;
                           exporter = next;
                           importer = vma;
                   } else if (end > next->vm_start) {
                           /*
                            * vma expands, overlapping part of the next:
                            * mprotect case 5 shifting the boundary up.
                            */
                           adjust_next = (end - next->vm_start) >> PAGE_SHIFT;
                           exporter = next;
                           importer = vma;
                   } else if (end < vma->vm_end) {
                           /*
                            * vma shrinks, and !insert tells it's not
                            * split_vma inserting another: so it must be
                            * mprotect case 4 shifting the boundary down.
                            */
                           adjust_next = - ((vma->vm_end - end) >> PAGE_SHIFT);
                           exporter = vma;
                           importer = next;
                   }
   
                   /*
                    * Easily overlooked: when mprotect shifts the boundary,
                    * make sure the expanding vma has anon_vma set if the
                    * shrinking vma had, to cover any anon pages imported.
                    */
                   if (exporter && exporter->anon_vma && !importer->anon_vma) {
                           if (anon_vma_clone(importer, exporter))
                                   return -ENOMEM;
                           importer->anon_vma = exporter->anon_vma;
                   }
           }
   
           if (file) {
                   mapping = file->f_mapping;
                   if (!(vma->vm_flags & VM_NONLINEAR)) {
                           root = &mapping->i_mmap;
                           uprobe_munmap(vma, vma->vm_start, vma->vm_end);
   
                           if (adjust_next)
                                   uprobe_munmap(next, next->vm_start,
                                                           next->vm_end);
                   }
   
                   mutex_lock(&mapping->i_mmap_mutex);
                   if (insert) {
                           /*
                            * Put into interval tree now, so instantiated pages
                            * are visible to arm/parisc __flush_dcache_page
                            * throughout; but we cannot insert into address
                            * space until vma start or end is updated.
                            */
                           __vma_link_file(insert);
                   }
           }
   
           vma_adjust_trans_huge(vma, start, end, adjust_next);
   
           anon_vma = vma->anon_vma;
           if (!anon_vma && adjust_next)
                   anon_vma = next->anon_vma;
           if (anon_vma) {
                   VM_BUG_ON(adjust_next && next->anon_vma &&
                             anon_vma != next->anon_vma);
                   anon_vma_lock_write(anon_vma);
                   anon_vma_interval_tree_pre_update_vma(vma);
                   if (adjust_next)
                           anon_vma_interval_tree_pre_update_vma(next);
           }
   
           if (root) {
                   flush_dcache_mmap_lock(mapping);
                   vma_interval_tree_remove(vma, root);
                   if (adjust_next)
                           vma_interval_tree_remove(next, root);
           }
   
           if (start != vma->vm_start) {
                   vma->vm_start = start;
                   start_changed = true;
           }
           if (end != vma->vm_end) {
                   vma->vm_end = end;
                   end_changed = true;
           }
           vma->vm_pgoff = pgoff;
           if (adjust_next) {
                   next->vm_start += adjust_next << PAGE_SHIFT;
                   next->vm_pgoff += adjust_next;
           }
   
           if (root) {
                   if (adjust_next)
                           vma_interval_tree_insert(next, root);
                   vma_interval_tree_insert(vma, root);
                   flush_dcache_mmap_unlock(mapping);
           }
   
           if (remove_next) {
                   /*
                    * vma_merge has merged next into vma, and needs
                    * us to remove next before dropping the locks.
                    */
                   __vma_unlink(mm, next, vma);
                   if (file)
                           __remove_shared_vm_struct(next, file, mapping);
           } else if (insert) {
                   /*
                    * split_vma has split insert from vma, and needs
                    * us to insert it before dropping the locks
                    * (it may either follow vma or precede it).
                    */
                   __insert_vm_struct(mm, insert);
           } else {
                   if (start_changed)
                           vma_gap_update(vma);
                   if (end_changed) {
                           if (!next)
                                   mm->highest_vm_end = end;
                           else if (!adjust_next)
                                   vma_gap_update(next);
                   }
           }
   
           if (anon_vma) {
                   anon_vma_interval_tree_post_update_vma(vma);
                   if (adjust_next)
                           anon_vma_interval_tree_post_update_vma(next);
                   anon_vma_unlock(anon_vma);
           }
           if (mapping)
                   mutex_unlock(&mapping->i_mmap_mutex);
   
           if (root) {
                   uprobe_mmap(vma);
   
                   if (adjust_next)
                           uprobe_mmap(next);
           }
   
           if (remove_next) {
                   if (file) {
                           uprobe_munmap(next, next->vm_start, next->vm_end);
                           fput(file);
                   }
                   if (next->anon_vma)
                           anon_vma_merge(vma, next);
                   mm->map_count--;
                   mpol_put(vma_policy(next));
                   kmem_cache_free(vm_area_cachep, next);
                   /*
                    * In mprotect's case 6 (see comments on vma_merge),
                    * we must remove another next too. It would clutter
                    * up the code too much to do both in one go.
                    */
                   next = vma->vm_next;
                   if (remove_next == 2)
                           goto again;
                   else if (next)
                           vma_gap_update(next);
                   else
                           mm->highest_vm_end = end;
           }
           if (insert && file)
                   uprobe_mmap(insert);
   
           validate_mm(mm);
   
           return 0;
   }
   
   /*
    * If the vma has a ->close operation then the driver probably needs to release
    * per-vma resources, so we don't attempt to merge those.
    */
   static inline int is_mergeable_vma(struct vm_area_struct *vma,
                           struct file *file, unsigned long vm_flags)
   {
           if (vma->vm_flags ^ vm_flags)
                   return 0;
           if (vma->vm_file != file)
                   return 0;
           if (vma->vm_ops && vma->vm_ops->close)
                   return 0;
           return 1;
   }
   
   static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
                                           struct anon_vma *anon_vma2,
                                           struct vm_area_struct *vma)
   {
           /*
            * The list_is_singular() test is to avoid merging VMA cloned from
            * parents. This can improve scalability caused by anon_vma lock.
            */
           if ((!anon_vma1 || !anon_vma2) && (!vma ||
                   list_is_singular(&vma->anon_vma_chain)))
                   return 1;
           return anon_vma1 == anon_vma2;
   }
   
   /*
    * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
    * in front of (at a lower virtual address and file offset than) the vma.
    *
    * We cannot merge two vmas if they have differently assigned (non-NULL)
    * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
    *
    * We don't check here for the merged mmap wrapping around the end of pagecache
    * indices (16TB on ia32) because do_mmap_pgoff() does not permit mmap's which
    * wrap, nor mmaps which cover the final page at index -1UL.
    */
   static int
   can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
           struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
   {
           if (is_mergeable_vma(vma, file, vm_flags) &&
               is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
                   if (vma->vm_pgoff == vm_pgoff)
                           return 1;
           }
           return 0;
   }
   
   /*
    * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
    * beyond (at a higher virtual address and file offset than) the vma.
    *
    * We cannot merge two vmas if they have differently assigned (non-NULL)
    * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
    */
   static int
   can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
           struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
   {
           if (is_mergeable_vma(vma, file, vm_flags) &&
               is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
                   pgoff_t vm_pglen;
                   vm_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
                   if (vma->vm_pgoff + vm_pglen == vm_pgoff)
                           return 1;
           }
           return 0;
   }
   
   /*
    * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
    * whether that can be merged with its predecessor or its successor.
    * Or both (it neatly fills a hole).
    *
    * In most cases - when called for mmap, brk or mremap - [addr,end) is
    * certain not to be mapped by the time vma_merge is called; but when
    * called for mprotect, it is certain to be already mapped (either at
    * an offset within prev, or at the start of next), and the flags of
    * this area are about to be changed to vm_flags - and the no-change
    * case has already been eliminated.
    *
    * The following mprotect cases have to be considered, where AAAA is
    * the area passed down from mprotect_fixup, never extending beyond one
    * vma, PPPPPP is the prev vma specified, and NNNNNN the next vma after:
    *
    *     AAAA             AAAA                AAAA          AAAA
    *    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPNNNNXXXX
    *    cannot merge    might become    might become    might become
    *                    PPNNNNNNNNNN    PPPPPPPPPPNN    PPPPPPPPPPPP 6 or
    *    mmap, brk or    case 4 below    case 5 below    PPPPPPPPXXXX 7 or
    *    mremap move:                                    PPPPNNNNNNNN 8
    *        AAAA
    *    PPPP    NNNN    PPPPPPPPPPPP    PPPPPPPPNNNN    PPPPNNNNNNNN
    *    might become    case 1 below    case 2 below    case 3 below
    *
    * Odd one out? Case 8, because it extends NNNN but needs flags of XXXX:
    * mprotect_fixup updates vm_flags & vm_page_prot on successful return.
    */
   struct vm_area_struct *vma_merge(struct mm_struct *mm,
                           struct vm_area_struct *prev, unsigned long addr,
                           unsigned long end, unsigned long vm_flags,
                           struct anon_vma *anon_vma, struct file *file,
                           pgoff_t pgoff, struct mempolicy *policy)
   {
           pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
           struct vm_area_struct *area, *next;
           int err;
   
           /*
            * We later require that vma->vm_flags == vm_flags,
            * so this tests vma->vm_flags & VM_SPECIAL, too.
            */
           if (vm_flags & VM_SPECIAL)
                   return NULL;
   
           if (prev)
                   next = prev->vm_next;
           else
                   next = mm->mmap;
           area = next;
           if (next && next->vm_end == end)                /* cases 6, 7, 8 */
                   next = next->vm_next;
   
           /*
            * Can it merge with the predecessor?
            */
           if (prev && prev->vm_end == addr &&
                           mpol_equal(vma_policy(prev), policy) &&
                           can_vma_merge_after(prev, vm_flags,
                                                   anon_vma, file, pgoff)) {
                   /*
                    * OK, it can.  Can we now merge in the successor as well?
                    */
                   if (next && end == next->vm_start &&
                                   mpol_equal(policy, vma_policy(next)) &&
                                   can_vma_merge_before(next, vm_flags,
                                           anon_vma, file, pgoff+pglen) &&
                                   is_mergeable_anon_vma(prev->anon_vma,
                                                         next->anon_vma, NULL)) {
                                                           /* cases 1, 6 */
                           err = vma_adjust(prev, prev->vm_start,
                                   next->vm_end, prev->vm_pgoff, NULL);
                   } else                                  /* cases 2, 5, 7 */
                           err = vma_adjust(prev, prev->vm_start,
                                   end, prev->vm_pgoff, NULL);
                   if (err)
                           return NULL;
                   khugepaged_enter_vma_merge(prev);
                   return prev;
          }
  
          /*
           * Can this new request be merged in front of next?
           */
          if (next && end == next->vm_start &&
                          mpol_equal(policy, vma_policy(next)) &&
                          can_vma_merge_before(next, vm_flags,
                                          anon_vma, file, pgoff+pglen)) {
                  if (prev && addr < prev->vm_end)        /* case 4 */
                          err = vma_adjust(prev, prev->vm_start,
                                  addr, prev->vm_pgoff, NULL);
                  else                                    /* cases 3, 8 */
                          err = vma_adjust(area, addr, next->vm_end,
                                  next->vm_pgoff - pglen, NULL);
                  if (err)
                          return NULL;
                  khugepaged_enter_vma_merge(area);
                  return area;
          }
  
          return NULL;
  }
  
  /*
   * Rough compatbility check to quickly see if it's even worth looking
   * at sharing an anon_vma.
   *
   * They need to have the same vm_file, and the flags can only differ
   * in things that mprotect may change.
   *
   * NOTE! The fact that we share an anon_vma doesn't _have_ to mean that
   * we can merge the two vma's. For example, we refuse to merge a vma if
   * there is a vm_ops->close() function, because that indicates that the
   * driver is doing some kind of reference counting. But that doesn't
   * really matter for the anon_vma sharing case.
   */
  static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
  {
          return a->vm_end == b->vm_start &&
                  mpol_equal(vma_policy(a), vma_policy(b)) &&
                  a->vm_file == b->vm_file &&
                  !((a->vm_flags ^ b->vm_flags) & ~(VM_READ|VM_WRITE|VM_EXEC)) &&
                  b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
  }
  
  /*
   * Do some basic sanity checking to see if we can re-use the anon_vma
   * from 'old'. The 'a'/'b' vma's are in VM order - one of them will be
   * the same as 'old', the other will be the new one that is trying
   * to share the anon_vma.
   *
   * NOTE! This runs with mm_sem held for reading, so it is possible that
   * the anon_vma of 'old' is concurrently in the process of being set up
   * by another page fault trying to merge _that_. But that's ok: if it
   * is being set up, that automatically means that it will be a singleton
   * acceptable for merging, so we can do all of this optimistically. But
   * we do that ACCESS_ONCE() to make sure that we never re-load the pointer.
   *
   * IOW: that the "list_is_singular()" test on the anon_vma_chain only
   * matters for the 'stable anon_vma' case (ie the thing we want to avoid
   * is to return an anon_vma that is "complex" due to having gone through
   * a fork).
   *
   * We also make sure that the two vma's are compatible (adjacent,
   * and with the same memory policies). That's all stable, even with just
   * a read lock on the mm_sem.
   */
  static struct anon_vma *reusable_anon_vma(struct vm_area_struct *old, struct vm_area_struct *a, struct vm_area_struct *b)
  {
          if (anon_vma_compatible(a, b)) {
                  struct anon_vma *anon_vma = ACCESS_ONCE(old->anon_vma);
  
                  if (anon_vma && list_is_singular(&old->anon_vma_chain))
                          return anon_vma;
          }
          return NULL;
  }
  
  /*
   * find_mergeable_anon_vma is used by anon_vma_prepare, to check
   * neighbouring vmas for a suitable anon_vma, before it goes off
   * to allocate a new anon_vma.  It checks because a repetitive
   * sequence of mprotects and faults may otherwise lead to distinct
   * anon_vmas being allocated, preventing vma merge in subsequent
   * mprotect.
   */
  struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
  {
          struct anon_vma *anon_vma;
          struct vm_area_struct *near;
  
          near = vma->vm_next;
          if (!near)
                  goto try_prev;
  
          anon_vma = reusable_anon_vma(near, vma, near);
          if (anon_vma)
                  return anon_vma;
  try_prev:
          near = vma->vm_prev;
          if (!near)
                  goto none;
  
          anon_vma = reusable_anon_vma(near, near, vma);
          if (anon_vma)
                  return anon_vma;
  none:
          /*
           * There's no absolute need to look only at touching neighbours:
           * we could search further afield for "compatible" anon_vmas.
           * But it would probably just be a waste of time searching,
           * or lead to too many vmas hanging off the same anon_vma.
           * We're trying to allow mprotect remerging later on,
           * not trying to minimize memory used for anon_vmas.
           */
          return NULL;
  }
  
  #ifdef CONFIG_PROC_FS
  void vm_stat_account(struct mm_struct *mm, unsigned long flags,
                                                  struct file *file, long pages)
  {
          const unsigned long stack_flags
                  = VM_STACK_FLAGS & (VM_GROWSUP|VM_GROWSDOWN);
  
          mm->total_vm += pages;
  
          if (file) {
                  mm->shared_vm += pages;
                  if ((flags & (VM_EXEC|VM_WRITE)) == VM_EXEC)
                          mm->exec_vm += pages;
          } else if (flags & stack_flags)
                  mm->stack_vm += pages;
  }
  #endif /* CONFIG_PROC_FS */
  
  /*
   * If a hint addr is less than mmap_min_addr change hint to be as
   * low as possible but still greater than mmap_min_addr
   */
  static inline unsigned long round_hint_to_min(unsigned long hint)
  {
          hint &= PAGE_MASK;
          if (((void *)hint != NULL) &&
              (hint < mmap_min_addr))
                  return PAGE_ALIGN(mmap_min_addr);
          return hint;
  }
  
  /*
   * The caller must hold down_write(&current->mm->mmap_sem).
   */
  
  unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
                          unsigned long len, unsigned long prot,
                          unsigned long flags, unsigned long pgoff)
  {
          struct mm_struct * mm = current->mm;
          struct inode *inode;
          vm_flags_t vm_flags;
  
          /*
           * Does the application expect PROT_READ to imply PROT_EXEC?
           *
           * (the exception is when the underlying filesystem is noexec
           *  mounted, in which case we dont add PROT_EXEC.)
           */
          if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
                  if (!(file && (file->f_path.mnt->mnt_flags & MNT_NOEXEC)))
                          prot |= PROT_EXEC;
  
          if (!len)
                  return -EINVAL;
  
          if (!(flags & MAP_FIXED))
                  addr = round_hint_to_min(addr);
  
          /* Careful about overflows.. */
          len = PAGE_ALIGN(len);
          if (!len)
                  return -ENOMEM;
  
          /* offset overflow? */
          if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
                 return -EOVERFLOW;
  
          /* Too many mappings? */
          if (mm->map_count > sysctl_max_map_count)
                  return -ENOMEM;
  
          /* Obtain the address to map to. we verify (or select) it and ensure
           * that it represents a valid section of the address space.
           */
          addr = get_unmapped_area(file, addr, len, pgoff, flags);
          if (addr & ~PAGE_MASK)
                  return addr;
  
          /* Do simple checking here so the lower-level routines won't have
           * to. we assume access permissions have been handled by the open
           * of the memory object, so we don't do any here.
           */
          vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags) |
                          mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
  
          if (flags & MAP_LOCKED)
                  if (!can_do_mlock())
                          return -EPERM;
  
          /* mlock MCL_FUTURE? */
          if (vm_flags & VM_LOCKED) {
                  unsigned long locked, lock_limit;
                  locked = len >> PAGE_SHIFT;
                  locked += mm->locked_vm;
                  lock_limit = rlimit(RLIMIT_MEMLOCK);
                  lock_limit >>= PAGE_SHIFT;
                  if (locked > lock_limit && !capable(CAP_IPC_LOCK))
                          return -EAGAIN;
          }
  
          inode = file ? file->f_path.dentry->d_inode : NULL;
  
          if (file) {
                  switch (flags & MAP_TYPE) {
                  case MAP_SHARED:
                          if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
                                  return -EACCES;
  
                          /*
                           * Make sure we don't allow writing to an append-only
                           * file..
                           */
                          if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
                                  return -EACCES;
  
                          /*
                           * Make sure there are no mandatory locks on the file.
                           */
                          if (locks_verify_locked(inode))
                                  return -EAGAIN;
  
                          vm_flags |= VM_SHARED | VM_MAYSHARE;
                          if (!(file->f_mode & FMODE_WRITE))
                                  vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
  
                          /* fall through */
                  case MAP_PRIVATE:
                          if (!(file->f_mode & FMODE_READ))
                                  return -EACCES;
                          if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) {
                                  if (vm_flags & VM_EXEC)
                                          return -EPERM;
                                  vm_flags &= ~VM_MAYEXEC;
                          }
  
                          if (!file->f_op || !file->f_op->mmap)
                                  return -ENODEV;
                          break;
  
                  default:
                          return -EINVAL;
                  }
          } else {
                  switch (flags & MAP_TYPE) {
                  case MAP_SHARED:
                          /*
                           * Ignore pgoff.
                           */
                          pgoff = 0;
                          vm_flags |= VM_SHARED | VM_MAYSHARE;
                          break;
                  case MAP_PRIVATE:
                          /*
                           * Set pgoff according to addr for anon_vma.
                           */
                          pgoff = addr >> PAGE_SHIFT;
                          break;
                  default:
                          return -EINVAL;
                  }
          }
  
          return mmap_region(file, addr, len, flags, vm_flags, pgoff);
  }
  
  SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
                  unsigned long, prot, unsigned long, flags,
                  unsigned long, fd, unsigned long, pgoff)
  {
          struct file *file = NULL;
          unsigned long retval = -EBADF;
  
          if (!(flags & MAP_ANONYMOUS)) {
                  audit_mmap_fd(fd, flags);
                  if (unlikely(flags & MAP_HUGETLB))
                          return -EINVAL;
                  file = fget(fd);
                  if (!file)
                          goto out;
          } else if (flags & MAP_HUGETLB) {
                  struct user_struct *user = NULL;
                  /*
                   * VM_NORESERVE is used because the reservations will be
                   * taken when vm_ops->mmap() is called
                   * A dummy user value is used because we are not locking
                   * memory so no accounting is necessary
                   */
                  file = hugetlb_file_setup(HUGETLB_ANON_FILE, addr, len,
                                  VM_NORESERVE,
                                  &user, HUGETLB_ANONHUGE_INODE,
                                  (flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
                  if (IS_ERR(file))
                          return PTR_ERR(file);
          }
  
          flags &= ~(MAP_EXECUTABLE | MAP_DENYWRITE);
  
          retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
          if (file)
                  fput(file);
  out:
          return retval;
  }
  
  #ifdef __ARCH_WANT_SYS_OLD_MMAP
  struct mmap_arg_struct {
          unsigned long addr;
          unsigned long len;
          unsigned long prot;
          unsigned long flags;
          unsigned long fd;
          unsigned long offset;
  };
  
  SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
  {
          struct mmap_arg_struct a;
  
          if (copy_from_user(&a, arg, sizeof(a)))
                  return -EFAULT;
          if (a.offset & ~PAGE_MASK)
                  return -EINVAL;
  
          return sys_mmap_pgoff(a.addr, a.len, a.prot, a.flags, a.fd,
                                a.offset >> PAGE_SHIFT);
  }
  #endif /* __ARCH_WANT_SYS_OLD_MMAP */
  
  /*
   * Some shared mappigns will want the pages marked read-only
   * to track write events. If so, we'll downgrade vm_page_prot
   * to the private version (using protection_map[] without the
   * VM_SHARED bit).
   */
  int vma_wants_writenotify(struct vm_area_struct *vma)
  {
          vm_flags_t vm_flags = vma->vm_flags;
  
          /* If it was private or non-writable, the write bit is already clear */
          if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED)))
                  return 0;
  
          /* The backer wishes to know when pages are first written to? */
          if (vma->vm_ops && vma->vm_ops->page_mkwrite)
                  return 1;
  
          /* The open routine did something to the protections already? */
          if (pgprot_val(vma->vm_page_prot) !=
              pgprot_val(vm_get_page_prot(vm_flags)))
                  return 0;
  
          /* Specialty mapping? */
          if (vm_flags & VM_PFNMAP)
                  return 0;
  
          /* Can the mapping track the dirty pages? */
          return vma->vm_file && vma->vm_file->f_mapping &&
                  mapping_cap_account_dirty(vma->vm_file->f_mapping);
  }
  
  /*
   * We account for memory if it's a private writeable mapping,
   * not hugepages and VM_NORESERVE wasn't set.
   */
  static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
  {
          /*
           * hugetlb has its own accounting separate from the core VM
           * VM_HUGETLB may not be set yet so we cannot check for that flag.
           */
          if (file && is_file_hugepages(file))
                  return 0;
  
          return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
  }
  
  unsigned long mmap_region(struct file *file, unsigned long addr,
                            unsigned long len, unsigned long flags,
                            vm_flags_t vm_flags, unsigned long pgoff)
  {
          struct mm_struct *mm = current->mm;
          struct vm_area_struct *vma, *prev;
          int correct_wcount = 0;
          int error;
          struct rb_node **rb_link, *rb_parent;
          unsigned long charged = 0;
          struct inode *inode =  file ? file->f_path.dentry->d_inode : NULL;
  
          /* Clear old maps */
          error = -ENOMEM;
  munmap_back:
          if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) {
                  if (do_munmap(mm, addr, len))
                          return -ENOMEM;
                  goto munmap_back;
          }
  
          /* Check against address space limit. */
          if (!may_expand_vm(mm, len >> PAGE_SHIFT))
                  return -ENOMEM;
  
          /*
           * Set 'VM_NORESERVE' if we should not account for the
           * memory use of this mapping.
           */
          if ((flags & MAP_NORESERVE)) {
                  /* We honor MAP_NORESERVE if allowed to overcommit */
                  if (sysctl_overcommit_memory != OVERCOMMIT_NEVER)
                          vm_flags |= VM_NORESERVE;
  
                  /* hugetlb applies strict overcommit unless MAP_NORESERVE */
                  if (file && is_file_hugepages(file))
                          vm_flags |= VM_NORESERVE;
          }
  
          /*
           * Private writable mapping: check memory availability
           */
          if (accountable_mapping(file, vm_flags)) {
                  charged = len >> PAGE_SHIFT;
                  if (security_vm_enough_memory_mm(mm, charged))
                          return -ENOMEM;
                  vm_flags |= VM_ACCOUNT;
          }
  
          /*
           * Can we just expand an old mapping?
           */
          vma = vma_merge(mm, prev, addr, addr + len, vm_flags, NULL, file, pgoff, NULL);
          if (vma)
                  goto out;
  
          /*
           * Determine the object being mapped and call the appropriate
           * specific mapper. the address has already been validated, but
           * not unmapped, but the maps are removed from the list.
           */
          vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
          if (!vma) {
                  error = -ENOMEM;
                  goto unacct_error;
          }
  
          vma->vm_mm = mm;
          vma->vm_start = addr;
          vma->vm_end = addr + len;
          vma->vm_flags = vm_flags;
          vma->vm_page_prot = vm_get_page_prot(vm_flags);
          vma->vm_pgoff = pgoff;
          INIT_LIST_HEAD(&vma->anon_vma_chain);
  
          error = -EINVAL;        /* when rejecting VM_GROWSDOWN|VM_GROWSUP */
  
          if (file) {
                  if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                          goto free_vma;
                  if (vm_flags & VM_DENYWRITE) {
                          error = deny_write_access(file);
                          if (error)
                                  goto free_vma;
                          correct_wcount = 1;
                  }
                  vma->vm_file = get_file(file);
                  error = file->f_op->mmap(file, vma);
                  if (error)
                          goto unmap_and_free_vma;
  
                  /* Can addr have changed??
                   *
                   * Answer: Yes, several device drivers can do it in their
                   *         f_op->mmap method. -DaveM
                   * Bug: If addr is changed, prev, rb_link, rb_parent should
                   *      be updated for vma_link()
                   */
                  WARN_ON_ONCE(addr != vma->vm_start);
  
                  addr = vma->vm_start;
                  pgoff = vma->vm_pgoff;
                  vm_flags = vma->vm_flags;
          } else if (vm_flags & VM_SHARED) {
                  if (unlikely(vm_flags & (VM_GROWSDOWN|VM_GROWSUP)))
                          goto free_vma;
                  error = shmem_zero_setup(vma);
                  if (error)
                          goto free_vma;
          }
  
          if (vma_wants_writenotify(vma)) {
                  pgprot_t pprot = vma->vm_page_prot;
  
                  /* Can vma->vm_page_prot have changed??
                   *
                   * Answer: Yes, drivers may have changed it in their
                   *         f_op->mmap method.
                   *
                   * Ensures that vmas marked as uncached stay that way.
                   */
                  vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);
                  if (pgprot_val(pprot) == pgprot_val(pgprot_noncached(pprot)))
                          vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
          }
  
          vma_link(mm, vma, prev, rb_link, rb_parent);
          file = vma->vm_file;
  
          /* Once vma denies write, undo our temporary denial count */
          if (correct_wcount)
                  atomic_inc(&inode->i_writecount);
  out:
          perf_event_mmap(vma);
  
          vm_stat_account(mm, vm_flags, file, len >> PAGE_SHIFT);
          if (vm_flags & VM_LOCKED) {
                  if (!mlock_vma_pages_range(vma, addr, addr + len))
                          mm->locked_vm += (len >> PAGE_SHIFT);
          } else if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK))
                  make_pages_present(addr, addr + len);
  
          if (file)
                  uprobe_mmap(vma);
  
          return addr;
  
  unmap_and_free_vma:
          if (correct_wcount)
                  atomic_inc(&inode->i_writecount);
          vma->vm_file = NULL;
          fput(file);
  
          /* Undo any partial mapping done by a device driver. */
          unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
          charged = 0;
  free_vma:
          kmem_cache_free(vm_area_cachep, vma);
  unacct_error:
          if (charged)
                  vm_unacct_memory(charged);
          return error;
  }
  
  unsigned long unmapped_area(struct vm_unmapped_area_info *info)
  {
          /*
           * We implement the search by looking for an rbtree node that
           * immediately follows a suitable gap. That is,
           * - gap_start = vma->vm_prev->vm_end <= info->high_limit - length;
           * - gap_end   = vma->vm_start        >= info->low_limit  + length;
           * - gap_end - gap_start >= length
           */
  
          struct mm_struct *mm = current->mm;
          struct vm_area_struct *vma;
          unsigned long length, low_limit, high_limit, gap_start, gap_end;
  
          /* Adjust search length to account for worst case alignment overhead */
          length = info->length + info->align_mask;
          if (length < info->length)
                  return -ENOMEM;
  
          /* Adjust search limits by the desired length */
          if (info->high_limit < length)
                  return -ENOMEM;
          high_limit = info->high_limit - length;
  
          if (info->low_limit > high_limit)
                  return -ENOMEM;
          low_limit = info->low_limit + length;
  
          /* Check if rbtree root looks promising */
          if (RB_EMPTY_ROOT(&mm->mm_rb))
                  goto check_highest;
          vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
          if (vma->rb_subtree_gap < length)
                  goto check_highest;
  
          while (true) {
                  /* Visit left subtree if it looks promising */
                  gap_end = vma->vm_start;
                  if (gap_end >= low_limit && vma->vm_rb.rb_left) {
                          struct vm_area_struct *left =
                                  rb_entry(vma->vm_rb.rb_left,
                                           struct vm_area_struct, vm_rb);
                          if (left->rb_subtree_gap >= length) {
                                  vma = left;
                                  continue;
                          }
                  }
  
                  gap_start = vma->vm_prev ? vma->vm_prev->vm_end : 0;
  check_current:
                  /* Check if current node has a suitable gap */
                  if (gap_start > high_limit)
                          return -ENOMEM;
                  if (gap_end >= low_limit && gap_end - gap_start >= length)
                          goto found;
  
                  /* Visit right subtree if it looks promising */
                  if (vma->vm_rb.rb_right) {
                          struct vm_area_struct *right =
                                  rb_entry(vma->vm_rb.rb_right,
                                           struct vm_area_struct, vm_rb);
                          if (right->rb_subtree_gap >= length) {
                                  vma = right;
                                  continue;
                          }
                  }
  
                  /* Go back up the rbtree to find next candidate node */
                  while (true) {
                          struct rb_node *prev = &vma->vm_rb;
                          if (!rb_parent(prev))
                                  goto check_highest;
                          vma = rb_entry(rb_parent(prev),
                                         struct vm_area_struct, vm_rb);
                          if (prev == vma->vm_rb.rb_left) {
                                  gap_start = vma->vm_prev->vm_end;
                                  gap_end = vma->vm_start;
                                  goto check_current;
                          }
                  }
          }
  
  check_highest:
          /* Check highest gap, which does not precede any rbtree node */
          gap_start = mm->highest_vm_end;
          gap_end = ULONG_MAX;  /* Only for VM_BUG_ON below */
          if (gap_start > high_limit)
                  return -ENOMEM;
  
  found:
          /* We found a suitable gap. Clip it with the original low_limit. */
          if (gap_start < info->low_limit)
                  gap_start = info->low_limit;
  
          /* Adjust gap address to the desired alignment */
          gap_start += (info->align_offset - gap_start) & info->align_mask;
  
          VM_BUG_ON(gap_start + info->length > info->high_limit);
          VM_BUG_ON(gap_start + info->length > gap_end);
          return gap_start;
  }
  
  unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
  {
          struct mm_struct *mm = current->mm;
          struct vm_area_struct *vma;
          unsigned long length, low_limit, high_limit, gap_start, gap_end;
  
          /* Adjust search length to account for worst case alignment overhead */
          length = info->length + info->align_mask;
          if (length < info->length)
                  return -ENOMEM;
  
          /*
           * Adjust search limits by the desired length.
           * See implementation comment at top of unmapped_area().
           */
          gap_end = info->high_limit;
          if (gap_end < length)
                  return -ENOMEM;
          high_limit = gap_end - length;
  
          if (info->low_limit > high_limit)
                  return -ENOMEM;
          low_limit = info->low_limit + length;
  
          /* Check highest gap, which does not precede any rbtree node */
          gap_start = mm->highest_vm_end;
          if (gap_start <= high_limit)
                  goto found_highest;
  
          /* Check if rbtree root looks promising */
          if (RB_EMPTY_ROOT(&mm->mm_rb))
                  return -ENOMEM;
          vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
          if (vma->rb_subtree_gap < length)
                  return -ENOMEM;
  
          while (true) {
                  /* Visit right subtree if it looks promising */
                  gap_start = vma->vm_prev ? vma->vm_prev->vm_end : 0;
                  if (gap_start <= high_limit && vma->vm_rb.rb_right) {
                          struct vm_area_struct *right =
                                  rb_entry(vma->vm_rb.rb_right,
                                           struct vm_area_struct, vm_rb);
                          if (right->rb_subtree_gap >= length) {
                                  vma = right;
                                  continue;
                          }
                  }
  
  check_current:
                  /* Check if current node has a suitable gap */
                  gap_end = vma->vm_start;
                  if (gap_end < low_limit)
                          return -ENOMEM;
                  if (gap_start <= high_limit && gap_end - gap_start >= length)
                          goto found;
  
                  /* Visit left subtree if it looks promising */
                  if (vma->vm_rb.rb_left) {
                          struct vm_area_struct *left =
                                  rb_entry(vma->vm_rb.rb_left,
                                           struct vm_area_struct, vm_rb);
                          if (left->rb_subtree_gap >= length) {
                                  vma = left;
                                  continue;
                          }
                  }
  
                  /* Go back up the rbtree to find next candidate node */
                  while (true) {
                          struct rb_node *prev = &vma->vm_rb;
                          if (!rb_parent(prev))
                                  return -ENOMEM;
                          vma = rb_entry(rb_parent(prev),
                                         struct vm_area_struct, vm_rb);
                          if (prev == vma->vm_rb.rb_right) {
                                  gap_start = vma->vm_prev ?
                                          vma->vm_prev->vm_end : 0;
                                  goto check_current;
                          }
                  }
          }
  
  found:
          /* We found a suitable gap. Clip it with the original high_limit. */
          if (gap_end > info->high_limit)
                  gap_end = info->high_limit;
  
  found_highest:
          /* Compute highest gap address at the desired alignment */
          gap_end -= info->length;
          gap_end -= (gap_end - info->align_offset) & info->align_mask;
  
          VM_BUG_ON(gap_end < info->low_limit);
          VM_BUG_ON(gap_end < gap_start);
          return gap_end;
  }
  
  /* Get an address range which is currently unmapped.
   * For shmat() with addr=0.
   *
   * Ugly calling convention alert:
   * Return value with the low bits set means error value,
   * ie
   *      if (ret & ~PAGE_MASK)
   *              error = ret;
   *
   * This function "knows" that -ENOMEM has the bits set.
   */
  #ifndef HAVE_ARCH_UNMAPPED_AREA
  unsigned long
  arch_get_unmapped_area(struct file *filp, unsigned long addr,
                  unsigned long len, unsigned long pgoff, unsigned long flags)
  {
          struct mm_struct *mm = current->mm;
          struct vm_area_struct *vma;
          struct vm_unmapped_area_info info;
  
          if (len > TASK_SIZE)
                  return -ENOMEM;
  
          if (flags & MAP_FIXED)
                  return addr;
  
          if (addr) {
                  addr = PAGE_ALIGN(addr);
                  vma = find_vma(mm, addr);
                  if (TASK_SIZE - len >= addr &&
                      (!vma || addr + len <= vma->vm_start))
                          return addr;
          }
  
          info.flags = 0;
          info.length = len;
          info.low_limit = TASK_UNMAPPED_BASE;
          info.high_limit = TASK_SIZE;
          info.align_mask = 0;
          return vm_unmapped_area(&info);
  }
  #endif  
  
  void arch_unmap_area(struct mm_struct *mm, unsigned long addr)
  {
          /*
           * Is this a new hole at the lowest possible address?
           */
          if (addr >= TASK_UNMAPPED_BASE && addr < mm->free_area_cache)
                  mm->free_area_cache = addr;
  }
  
  /*
   * This mmap-allocator allocates new areas top-down from below the
   * stack's low limit (the base):
   */
  #ifndef HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
  unsigned long
  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
                            const unsigned long len, const unsigned long pgoff,
                            const unsigned long flags)
  {
          struct vm_area_struct *vma;
          struct mm_struct *mm = current->mm;
          unsigned long addr = addr0;
          struct vm_unmapped_area_info info;
  
          /* requested length too big for entire address space */
          if (len > TASK_SIZE)
                  return -ENOMEM;
  
          if (flags & MAP_FIXED)
                  return addr;
  
          /* requesting a specific address */
          if (addr) {
                  addr = PAGE_ALIGN(addr);
                  vma = find_vma(mm, addr);
                  if (TASK_SIZE - len >= addr &&
                                  (!vma || addr + len <= vma->vm_start))
                          return addr;
          }
  
          info.flags = VM_UNMAPPED_AREA_TOPDOWN;
          info.length = len;
          info.low_limit = PAGE_SIZE;
          info.high_limit = mm->mmap_base;
          info.align_mask = 0;
          addr = vm_unmapped_area(&info);
  
          /*
           * A failed mmap() very likely causes application failure,
           * so fall back to the bottom-up function here. This scenario
           * can happen with large stack limits and large mmap()
           * allocations.
           */
          if (addr & ~PAGE_MASK) {
                  VM_BUG_ON(addr != -ENOMEM);
                  info.flags = 0;
                  info.low_limit = TASK_UNMAPPED_BASE;
                  info.high_limit = TASK_SIZE;
                  addr = vm_unmapped_area(&info);
          }
  
          return addr;
  }
  #endif
  
  void arch_unmap_area_topdown(struct mm_struct *mm, unsigned long addr)
  {
          /*
           * Is this a new hole at the highest possible address?
           */
          if (addr > mm->free_area_cache)
                  mm->free_area_cache = addr;
  
          /* dont allow allocations above current base */
          if (mm->free_area_cache > mm->mmap_base)
                  mm->free_area_cache = mm->mmap_base;
  }
  
  unsigned long
  get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
                  unsigned long pgoff, unsigned long flags)
  {
          unsigned long (*get_area)(struct file *, unsigned long,
                                    unsigned long, unsigned long, unsigned long);
  
          unsigned long error = arch_mmap_check(addr, len, flags);
          if (error)
                  return error;
  
          /* Careful about overflows.. */
          if (len > TASK_SIZE)
                  return -ENOMEM;
  
          get_area = current->mm->get_unmapped_area;
          if (file && file->f_op && file->f_op->get_unmapped_area)
                  get_area = file->f_op->get_unmapped_area;
          addr = get_area(file, addr, len, pgoff, flags);
          if (IS_ERR_VALUE(addr))
                  return addr;
  
          if (addr > TASK_SIZE - len)
                  return -ENOMEM;
          if (addr & ~PAGE_MASK)
                  return -EINVAL;
  
          addr = arch_rebalance_pgtables(addr, len);
          error = security_mmap_addr(addr);
          return error ? error : addr;
  }
  
  EXPORT_SYMBOL(get_unmapped_area);
  
  /* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
  struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
  {
          struct vm_area_struct *vma = NULL;
  
          if (WARN_ON_ONCE(!mm))          /* Remove this in linux-3.6 */
                  return NULL;
  
          /* Check the cache first. */
          /* (Cache hit rate is typically around 35%.) */
          vma = mm->mmap_cache;
          if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
                  struct rb_node *rb_node;
  
                  rb_node = mm->mm_rb.rb_node;
                  vma = NULL;
  
                  while (rb_node) {
                          struct vm_area_struct *vma_tmp;
  
                          vma_tmp = rb_entry(rb_node,
                                             struct vm_area_struct, vm_rb);
  
                          if (vma_tmp->vm_end > addr) {
                                  vma = vma_tmp;
                                  if (vma_tmp->vm_start <= addr)
                                          break;
                                  rb_node = rb_node->rb_left;
                          } else
                                  rb_node = rb_node->rb_right;
                  }
                  if (vma)
                          mm->mmap_cache = vma;
          }
          return vma;
  }
  
  EXPORT_SYMBOL(find_vma);
  
  /*
   * Same as find_vma, but also return a pointer to the previous VMA in *pprev.
   */
  struct vm_area_struct *
  find_vma_prev(struct mm_struct *mm, unsigned long addr,
                          struct vm_area_struct **pprev)
  {
          struct vm_area_struct *vma;
  
          vma = find_vma(mm, addr);
          if (vma) {
                  *pprev = vma->vm_prev;
          } else {
                  struct rb_node *rb_node = mm->mm_rb.rb_node;
                  *pprev = NULL;
                  while (rb_node) {
                          *pprev = rb_entry(rb_node, struct vm_area_struct, vm_rb);
                          rb_node = rb_node->rb_right;
                  }
          }
          return vma;
  }
  
  /*
   * Verify that the stack growth is acceptable and
   * update accounting. This is shared with both the
   * grow-up and grow-down cases.
   */
  static int acct_stack_growth(struct vm_area_struct *vma, unsigned long size, unsigned long grow)
  {
          struct mm_struct *mm = vma->vm_mm;
          struct rlimit *rlim = current->signal->rlim;
          unsigned long new_start;
  
          /* address space limit tests */
          if (!may_expand_vm(mm, grow))
                  return -ENOMEM;
  
          /* Stack limit test */
          if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur))
                  return -ENOMEM;
  
          /* mlock limit tests */
          if (vma->vm_flags & VM_LOCKED) {
                  unsigned long locked;
                  unsigned long limit;
                  locked = mm->locked_vm + grow;
                  limit = ACCESS_ONCE(rlim[RLIMIT_MEMLOCK].rlim_cur);
                  limit >>= PAGE_SHIFT;
                  if (locked > limit && !capable(CAP_IPC_LOCK))
                          return -ENOMEM;
          }
  
          /* Check to ensure the stack will not grow into a hugetlb-only region */
          new_start = (vma->vm_flags & VM_GROWSUP) ? vma->vm_start :
                          vma->vm_end - size;
          if (is_hugepage_only_range(vma->vm_mm, new_start, size))
                  return -EFAULT;
  
          /*
           * Overcommit..  This must be the final test, as it will
           * update security statistics.
           */
          if (security_vm_enough_memory_mm(mm, grow))
                  return -ENOMEM;
  
          /* Ok, everything looks good - let it rip */
          if (vma->vm_flags & VM_LOCKED)
                  mm->locked_vm += grow;
          vm_stat_account(mm, vma->vm_flags, vma->vm_file, grow);
          return 0;
  }
  
  #if defined(CONFIG_STACK_GROWSUP) || defined(CONFIG_IA64)
  /*
   * PA-RISC uses this for its stack; IA64 for its Register Backing Store.
   * vma is the last one with address > vma->vm_end.  Have to extend vma.
   */
  int expand_upwards(struct vm_area_struct *vma, unsigned long address)
  {
          int error;
  
          if (!(vma->vm_flags & VM_GROWSUP))
                  return -EFAULT;
  
          /*
           * We must make sure the anon_vma is allocated
           * so that the anon_vma locking is not a noop.
           */
          if (unlikely(anon_vma_prepare(vma)))
                  return -ENOMEM;
          vma_lock_anon_vma(vma);
  
          /*
           * vma->vm_start/vm_end cannot change under us because the caller
           * is required to hold the mmap_sem in read mode.  We need the
           * anon_vma lock to serialize against concurrent expand_stacks.
           * Also guard against wrapping around to address 0.
           */
          if (address < PAGE_ALIGN(address+4))
                  address = PAGE_ALIGN(address+4);
          else {
                  vma_unlock_anon_vma(vma);
                  return -ENOMEM;
          }
          error = 0;
  
          /* Somebody else might have raced and expanded it already */
          if (address > vma->vm_end) {
                  unsigned long size, grow;
  
                  size = address - vma->vm_start;
                  grow = (address - vma->vm_end) >> PAGE_SHIFT;
  
                  error = -ENOMEM;
                  if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) {
                          error = acct_stack_growth(vma, size, grow);
                          if (!error) {
                                  /*
                                   * vma_gap_update() doesn't support concurrent
                                   * updates, but we only hold a shared mmap_sem
                                   * lock here, so we need to protect against
                                   * concurrent vma expansions.
                                   * vma_lock_anon_vma() doesn't help here, as
                                   * we don't guarantee that all growable vmas
                                   * in a mm share the same root anon vma.
                                   * So, we reuse mm->page_table_lock to guard
                                   * against concurrent vma expansions.
                                   */
                                  spin_lock(&vma->vm_mm->page_table_lock);
                                  anon_vma_interval_tree_pre_update_vma(vma);
                                  vma->vm_end = address;
                                  anon_vma_interval_tree_post_update_vma(vma);
                                  if (vma->vm_next)
                                          vma_gap_update(vma->vm_next);
                                  else
                                          vma->vm_mm->highest_vm_end = address;
                                  spin_unlock(&vma->vm_mm->page_table_lock);
  
                                  perf_event_mmap(vma);
                          }
                  }
          }
          vma_unlock_anon_vma(vma);
          khugepaged_enter_vma_merge(vma);
          validate_mm(vma->vm_mm);
          return error;
  }
  #endif /* CONFIG_STACK_GROWSUP || CONFIG_IA64 */
  
  /*
   * vma is the first one with address < vma->vm_start.  Have to extend vma.
   */
  int expand_downwards(struct vm_area_struct *vma,
                                     unsigned long address)
  {
          int error;
  
          /*
           * We must make sure the anon_vma is allocated
           * so that the anon_vma locking is not a noop.
           */
          if (unlikely(anon_vma_prepare(vma)))
                  return -ENOMEM;
  
          address &= PAGE_MASK;
          error = security_mmap_addr(address);
          if (error)
                  return error;
  
          vma_lock_anon_vma(vma);
  
          /*
           * vma->vm_start/vm_end cannot change under us because the caller
           * is required to hold the mmap_sem in read mode.  We need the
           * anon_vma lock to serialize against concurrent expand_stacks.
           */
  
          /* Somebody else might have raced and expanded it already */
          if (address < vma->vm_start) {
                  unsigned long size, grow;
  
                  size = vma->vm_end - address;
                  grow = (vma->vm_start - address) >> PAGE_SHIFT;
  
                  error = -ENOMEM;
                  if (grow <= vma->vm_pgoff) {
                          error = acct_stack_growth(vma, size, grow);
                          if (!error) {
                                  /*
                                   * vma_gap_update() doesn't support concurrent
                                   * updates, but we only hold a shared mmap_sem
                                   * lock here, so we need to protect against
                                   * concurrent vma expansions.
                                   * vma_lock_anon_vma() doesn't help here, as
                                   * we don't guarantee that all growable vmas
                                   * in a mm share the same root anon vma.
                                   * So, we reuse mm->page_table_lock to guard
                                   * against concurrent vma expansions.
                                   */
                                  spin_lock(&vma->vm_mm->page_table_lock);
                                  anon_vma_interval_tree_pre_update_vma(vma);
                                  vma->vm_start = address;
                                  vma->vm_pgoff -= grow;
                                  anon_vma_interval_tree_post_update_vma(vma);
                                  vma_gap_update(vma);
                                  spin_unlock(&vma->vm_mm->page_table_lock);
  
                                  perf_event_mmap(vma);
                          }
                  }
          }
          vma_unlock_anon_vma(vma);
          khugepaged_enter_vma_merge(vma);
          validate_mm(vma->vm_mm);
          return error;
  }
  
  #ifdef CONFIG_STACK_GROWSUP
  int expand_stack(struct vm_area_struct *vma, unsigned long address)
  {
          return expand_upwards(vma, address);
  }
  
  struct vm_area_struct *
  find_extend_vma(struct mm_struct *mm, unsigned long addr)
  {
          struct vm_area_struct *vma, *prev;
  
          addr &= PAGE_MASK;
          vma = find_vma_prev(mm, addr, &prev);
          if (vma && (vma->vm_start <= addr))
                  return vma;
          if (!prev || expand_stack(prev, addr))
                  return NULL;
          if (prev->vm_flags & VM_LOCKED) {
                  mlock_vma_pages_range(prev, addr, prev->vm_end);
          }
          return prev;
  }
  #else
  int expand_stack(struct vm_area_struct *vma, unsigned long address)
  {
          return expand_downwards(vma, address);
  }
  
  struct vm_area_struct *
  find_extend_vma(struct mm_struct * mm, unsigned long addr)
  {
          struct vm_area_struct * vma;
          unsigned long start;
  
          addr &= PAGE_MASK;
          vma = find_vma(mm,addr);
          if (!vma)
                  return NULL;
          if (vma->vm_start <= addr)
                  return vma;
          if (!(vma->vm_flags & VM_GROWSDOWN))
                  return NULL;
          start = vma->vm_start;
          if (expand_stack(vma, addr))
                  return NULL;
          if (vma->vm_flags & VM_LOCKED) {
                  mlock_vma_pages_range(vma, addr, start);
          }
          return vma;
  }
  #endif
  
  /*
   * Ok - we have the memory areas we should free on the vma list,
   * so release them, and do the vma updates.
   *
   * Called with the mm semaphore held.
   */
  static void remove_vma_list(struct mm_struct *mm, struct vm_area_struct *vma)
  {
          unsigned long nr_accounted = 0;
  
          /* Update high watermark before we lower total_vm */
          update_hiwater_vm(mm);
          do {
                  long nrpages = vma_pages(vma);
  
                  if (vma->vm_flags & VM_ACCOUNT)
                          nr_accounted += nrpages;
                  vm_stat_account(mm, vma->vm_flags, vma->vm_file, -nrpages);
                  vma = remove_vma(vma);
          } while (vma);
          vm_unacct_memory(nr_accounted);
          validate_mm(mm);
  }
  
  /*
   * Get rid of page table information in the indicated region.
   *
   * Called with the mm semaphore held.
   */
  static void unmap_region(struct mm_struct *mm,
                  struct vm_area_struct *vma, struct vm_area_struct *prev,
                  unsigned long start, unsigned long end)
  {
          struct vm_area_struct *next = prev? prev->vm_next: mm->mmap;
          struct mmu_gather tlb;
  
          lru_add_drain();
          tlb_gather_mmu(&tlb, mm, 0);
          update_hiwater_rss(mm);
          unmap_vmas(&tlb, vma, start, end);
          free_pgtables(&tlb, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
                                   next ? next->vm_start : 0);
          tlb_finish_mmu(&tlb, start, end);
  }
  
  /*
   * Create a list of vma's touched by the unmap, removing them from the mm's
   * vma list as we go..
   */
  static void
  detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
          struct vm_area_struct *prev, unsigned long end)
  {
          struct vm_area_struct **insertion_point;
          struct vm_area_struct *tail_vma = NULL;
          unsigned long addr;
  
          insertion_point = (prev ? &prev->vm_next : &mm->mmap);
          vma->vm_prev = NULL;
          do {
                  vma_rb_erase(vma, &mm->mm_rb);
                  mm->map_count--;
                  tail_vma = vma;
                  vma = vma->vm_next;
          } while (vma && vma->vm_start < end);
          *insertion_point = vma;
          if (vma) {
                  vma->vm_prev = prev;
                  vma_gap_update(vma);
          } else
                  mm->highest_vm_end = prev ? prev->vm_end : 0;
          tail_vma->vm_next = NULL;
          if (mm->unmap_area == arch_unmap_area)
                  addr = prev ? prev->vm_end : mm->mmap_base;
          else
                  addr = vma ?  vma->vm_start : mm->mmap_base;
          mm->unmap_area(mm, addr);
          mm->mmap_cache = NULL;          /* Kill the cache. */
  }
  
  /*
   * __split_vma() bypasses sysctl_max_map_count checking.  We use this on the
   * munmap path where it doesn't make sense to fail.
   */
  static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
                unsigned long addr, int new_below)
  {
          struct mempolicy *pol;
          struct vm_area_struct *new;
          int err = -ENOMEM;
  
          if (is_vm_hugetlb_page(vma) && (addr &
                                          ~(huge_page_mask(hstate_vma(vma)))))
                  return -EINVAL;
  
          new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
          if (!new)
                  goto out_err;
  
          /* most fields are the same, copy all, and then fixup */
          *new = *vma;
  
          INIT_LIST_HEAD(&new->anon_vma_chain);
  
          if (new_below)
                  new->vm_end = addr;
          else {
                  new->vm_start = addr;
                  new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
          }
  
          pol = mpol_dup(vma_policy(vma));
          if (IS_ERR(pol)) {
                  err = PTR_ERR(pol);
                  goto out_free_vma;
          }
          vma_set_policy(new, pol);
  
          if (anon_vma_clone(new, vma))
                  goto out_free_mpol;
  
          if (new->vm_file)
                  get_file(new->vm_file);
  
          if (new->vm_ops && new->vm_ops->open)
                  new->vm_ops->open(new);
  
          if (new_below)
                  err = vma_adjust(vma, addr, vma->vm_end, vma->vm_pgoff +
                          ((addr - new->vm_start) >> PAGE_SHIFT), new);
          else
                  err = vma_adjust(vma, vma->vm_start, addr, vma->vm_pgoff, new);
  
          /* Success. */
          if (!err)
                  return 0;
  
          /* Clean everything up if vma_adjust failed. */
          if (new->vm_ops && new->vm_ops->close)
                  new->vm_ops->close(new);
          if (new->vm_file)
                  fput(new->vm_file);
          unlink_anon_vmas(new);
   out_free_mpol:
          mpol_put(pol);
   out_free_vma:
          kmem_cache_free(vm_area_cachep, new);
   out_err:
          return err;
  }
  
  /*
   * Split a vma into two pieces at address 'addr', a new vma is allocated
   * either for the first part or the tail.
   */
  int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
                unsigned long addr, int new_below)
  {
          if (mm->map_count >= sysctl_max_map_count)
                  return -ENOMEM;
  
          return __split_vma(mm, vma, addr, new_below);
  }
  
  /* Munmap is split into 2 main parts -- this part which finds
   * what needs doing, and the areas themselves, which do the
   * work.  This now handles partial unmappings.
   * Jeremy Fitzhardinge <jeremy@goop.org>
   */
  int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
  {
          unsigned long end;
          struct vm_area_struct *vma, *prev, *last;
  
          if ((start & ~PAGE_MASK) || start > TASK_SIZE || len > TASK_SIZE-start)
                  return -EINVAL;
  
          if ((len = PAGE_ALIGN(len)) == 0)
                  return -EINVAL;
  
          /* Find the first overlapping VMA */
          vma = find_vma(mm, start);
          if (!vma)
                  return 0;
          prev = vma->vm_prev;
          /* we have  start < vma->vm_end  */
  
          /* if it doesn't overlap, we have nothing.. */
          end = start + len;
          if (vma->vm_start >= end)
                  return 0;
  
          /*
           * If we need to split any vma, do it now to save pain later.
           *
           * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
           * unmapped vm_area_struct will remain in use: so lower split_vma
           * places tmp vma above, and higher split_vma places tmp vma below.
           */
          if (start > vma->vm_start) {
                  int error;
  
                  /*
                   * Make sure that map_count on return from munmap() will
                   * not exceed its limit; but let map_count go just above
                   * its limit temporarily, to help free resources as expected.
                   */
                  if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
                          return -ENOMEM;
  
                  error = __split_vma(mm, vma, start, 0);
                  if (error)
                          return error;
                  prev = vma;
          }
  
          /* Does it split the last one? */
          last = find_vma(mm, end);
          if (last && end > last->vm_start) {
                  int error = __split_vma(mm, last, end, 1);
                  if (error)
                          return error;
          }
          vma = prev? prev->vm_next: mm->mmap;
  
          /*
           * unlock any mlock()ed ranges before detaching vmas
           */
          if (mm->locked_vm) {
                  struct vm_area_struct *tmp = vma;
                  while (tmp && tmp->vm_start < end) {
                          if (tmp->vm_flags & VM_LOCKED) {
                                  mm->locked_vm -= vma_pages(tmp);
                                  munlock_vma_pages_all(tmp);
                          }
                          tmp = tmp->vm_next;
                  }
          }
  
          /*
           * Remove the vma's, and unmap the actual pages
           */
          detach_vmas_to_be_unmapped(mm, vma, prev, end);
          unmap_region(mm, vma, prev, start, end);
  
          /* Fix up all other VM information */
          remove_vma_list(mm, vma);
  
          return 0;
  }
  
  int vm_munmap(unsigned long start, size_t len)
  {
          int ret;
          struct mm_struct *mm = current->mm;
  
          down_write(&mm->mmap_sem);
          ret = do_munmap(mm, start, len);
          up_write(&mm->mmap_sem);
          return ret;
  }
  EXPORT_SYMBOL(vm_munmap);
  
  SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
  {
          profile_munmap(addr);
          return vm_munmap(addr, len);
  }
  
  static inline void verify_mm_writelocked(struct mm_struct *mm)
  {
  #ifdef CONFIG_DEBUG_VM
          if (unlikely(down_read_trylock(&mm->mmap_sem))) {
                  WARN_ON(1);
                  up_read(&mm->mmap_sem);
          }
  #endif
  }
  
  /*
   *  this is really a simplified "do_mmap".  it only handles
   *  anonymous maps.  eventually we may be able to do some
   *  brk-specific accounting here.
   */
  static unsigned long do_brk(unsigned long addr, unsigned long len)
  {
          struct mm_struct * mm = current->mm;
          struct vm_area_struct * vma, * prev;
          unsigned long flags;
          struct rb_node ** rb_link, * rb_parent;
          pgoff_t pgoff = addr >> PAGE_SHIFT;
          int error;
  
          len = PAGE_ALIGN(len);
          if (!len)
                  return addr;
  
          flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
  
          error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
          if (error & ~PAGE_MASK)
                  return error;
  
          /*
           * mlock MCL_FUTURE?
           */
          if (mm->def_flags & VM_LOCKED) {
                  unsigned long locked, lock_limit;
                  locked = len >> PAGE_SHIFT;
                  locked += mm->locked_vm;
                  lock_limit = rlimit(RLIMIT_MEMLOCK);
                  lock_limit >>= PAGE_SHIFT;
                  if (locked > lock_limit && !capable(CAP_IPC_LOCK))
                          return -EAGAIN;
          }
  
          /*
           * mm->mmap_sem is required to protect against another thread
           * changing the mappings in case we sleep.
           */
          verify_mm_writelocked(mm);
  
          /*
           * Clear old maps.  this also does some error checking for us
           */
   munmap_back:
          if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) {
                  if (do_munmap(mm, addr, len))
                          return -ENOMEM;
                  goto munmap_back;
          }
  
          /* Check against address space limits *after* clearing old maps... */
          if (!may_expand_vm(mm, len >> PAGE_SHIFT))
                  return -ENOMEM;
  
          if (mm->map_count > sysctl_max_map_count)
                  return -ENOMEM;
  
          if (security_vm_enough_memory_mm(mm, len >> PAGE_SHIFT))
                  return -ENOMEM;
  
          /* Can we just expand an old private anonymous mapping? */
          vma = vma_merge(mm, prev, addr, addr + len, flags,
                                          NULL, NULL, pgoff, NULL);
          if (vma)
                  goto out;
  
          /*
           * create a vma struct for an anonymous mapping
           */
          vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
          if (!vma) {
                  vm_unacct_memory(len >> PAGE_SHIFT);
                  return -ENOMEM;
          }
  
          INIT_LIST_HEAD(&vma->anon_vma_chain);
          vma->vm_mm = mm;
          vma->vm_start = addr;
          vma->vm_end = addr + len;
          vma->vm_pgoff = pgoff;
          vma->vm_flags = flags;
          vma->vm_page_prot = vm_get_page_prot(flags);
          vma_link(mm, vma, prev, rb_link, rb_parent);
  out:
          perf_event_mmap(vma);
          mm->total_vm += len >> PAGE_SHIFT;
          if (flags & VM_LOCKED) {
                  if (!mlock_vma_pages_range(vma, addr, addr + len))
                          mm->locked_vm += (len >> PAGE_SHIFT);
          }
          return addr;
  }
  
  unsigned long vm_brk(unsigned long addr, unsigned long len)
  {
          struct mm_struct *mm = current->mm;
          unsigned long ret;
  
          down_write(&mm->mmap_sem);
          ret = do_brk(addr, len);
          up_write(&mm->mmap_sem);
          return ret;
  }
  EXPORT_SYMBOL(vm_brk);
  
  /* Release all mmaps. */
  void exit_mmap(struct mm_struct *mm)
  {
          struct mmu_gather tlb;
          struct vm_area_struct *vma;
          unsigned long nr_accounted = 0;
  
          /* mm's last user has gone, and its about to be pulled down */
          mmu_notifier_release(mm);
  
          if (mm->locked_vm) {
                  vma = mm->mmap;
                  while (vma) {
                          if (vma->vm_flags & VM_LOCKED)
                                  munlock_vma_pages_all(vma);
                          vma = vma->vm_next;
                  }
          }
  
          arch_exit_mmap(mm);
  
          vma = mm->mmap;
          if (!vma)       /* Can happen if dup_mmap() received an OOM */
                  return;
  
          lru_add_drain();
          flush_cache_mm(mm);
          tlb_gather_mmu(&tlb, mm, 1);
          /* update_hiwater_rss(mm) here? but nobody should be looking */
          /* Use -1 here to ensure all VMAs in the mm are unmapped */
          unmap_vmas(&tlb, vma, 0, -1);
  
          free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
          tlb_finish_mmu(&tlb, 0, -1);
  
          /*
           * Walk the list again, actually closing and freeing it,
           * with preemption enabled, without holding any MM locks.
           */
          while (vma) {
                  if (vma->vm_flags & VM_ACCOUNT)
                          nr_accounted += vma_pages(vma);
                  vma = remove_vma(vma);
          }
          vm_unacct_memory(nr_accounted);
  
          WARN_ON(mm->nr_ptes > (FIRST_USER_ADDRESS+PMD_SIZE-1)>>PMD_SHIFT);
  }
  
  /* Insert vm structure into process list sorted by address
   * and into the inode's i_mmap tree.  If vm_file is non-NULL
   * then i_mmap_mutex is taken here.
   */
  int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
  {
          struct vm_area_struct *prev;
          struct rb_node **rb_link, *rb_parent;
  
          /*
           * The vm_pgoff of a purely anonymous vma should be irrelevant
           * until its first write fault, when page's anon_vma and index
           * are set.  But now set the vm_pgoff it will almost certainly
           * end up with (unless mremap moves it elsewhere before that
           * first wfault), so /proc/pid/maps tells a consistent story.
           *
           * By setting it to reflect the virtual start address of the
           * vma, merges and splits can happen in a seamless way, just
           * using the existing file pgoff checks and manipulations.
           * Similarly in do_mmap_pgoff and in do_brk.
           */
          if (!vma->vm_file) {
                  BUG_ON(vma->anon_vma);
                  vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
          }
          if (find_vma_links(mm, vma->vm_start, vma->vm_end,
                             &prev, &rb_link, &rb_parent))
                  return -ENOMEM;
          if ((vma->vm_flags & VM_ACCOUNT) &&
               security_vm_enough_memory_mm(mm, vma_pages(vma)))
                  return -ENOMEM;
  
          vma_link(mm, vma, prev, rb_link, rb_parent);
          return 0;
  }
  
  /*
   * Copy the vma structure to a new location in the same mm,
   * prior to moving page table entries, to effect an mremap move.
   */
  struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
          unsigned long addr, unsigned long len, pgoff_t pgoff,
          bool *need_rmap_locks)
  {
          struct vm_area_struct *vma = *vmap;
          unsigned long vma_start = vma->vm_start;
          struct mm_struct *mm = vma->vm_mm;
          struct vm_area_struct *new_vma, *prev;
          struct rb_node **rb_link, *rb_parent;
          struct mempolicy *pol;
          bool faulted_in_anon_vma = true;
  
          /*
           * If anonymous vma has not yet been faulted, update new pgoff
           * to match new location, to increase its chance of merging.
           */
          if (unlikely(!vma->vm_file && !vma->anon_vma)) {
                  pgoff = addr >> PAGE_SHIFT;
                  faulted_in_anon_vma = false;
          }
  
          if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent))
                  return NULL;    /* should never get here */
          new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
                          vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
          if (new_vma) {
                  /*
                   * Source vma may have been merged into new_vma
                   */
                  if (unlikely(vma_start >= new_vma->vm_start &&
                               vma_start < new_vma->vm_end)) {
                          /*
                           * The only way we can get a vma_merge with
                           * self during an mremap is if the vma hasn't
                           * been faulted in yet and we were allowed to
                           * reset the dst vma->vm_pgoff to the
                           * destination address of the mremap to allow
                           * the merge to happen. mremap must change the
                           * vm_pgoff linearity between src and dst vmas
                           * (in turn preventing a vma_merge) to be
                           * safe. It is only safe to keep the vm_pgoff
                           * linear if there are no pages mapped yet.
                           */
                          VM_BUG_ON(faulted_in_anon_vma);
                          *vmap = vma = new_vma;
                  }
                  *need_rmap_locks = (new_vma->vm_pgoff <= vma->vm_pgoff);
          } else {
                  new_vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
                  if (new_vma) {
                          *new_vma = *vma;
                          new_vma->vm_start = addr;
                          new_vma->vm_end = addr + len;
                          new_vma->vm_pgoff = pgoff;
                          pol = mpol_dup(vma_policy(vma));
                          if (IS_ERR(pol))
                                  goto out_free_vma;
                          vma_set_policy(new_vma, pol);
                          INIT_LIST_HEAD(&new_vma->anon_vma_chain);
                          if (anon_vma_clone(new_vma, vma))
                                  goto out_free_mempol;
                          if (new_vma->vm_file)
                                  get_file(new_vma->vm_file);
                          if (new_vma->vm_ops && new_vma->vm_ops->open)
                                  new_vma->vm_ops->open(new_vma);
                          vma_link(mm, new_vma, prev, rb_link, rb_parent);
                          *need_rmap_locks = false;
                  }
          }
          return new_vma;
  
   out_free_mempol:
          mpol_put(pol);
   out_free_vma:
          kmem_cache_free(vm_area_cachep, new_vma);
          return NULL;
  }
  
  /*
   * Return true if the calling process may expand its vm space by the passed
   * number of pages
   */
  int may_expand_vm(struct mm_struct *mm, unsigned long npages)
  {
          unsigned long cur = mm->total_vm;       /* pages */
          unsigned long lim;
  
          lim = rlimit(RLIMIT_AS) >> PAGE_SHIFT;
  
          if (cur + npages > lim)
                  return 0;
          return 1;
  }
  
  
  static int special_mapping_fault(struct vm_area_struct *vma,
                                  struct vm_fault *vmf)
  {
          pgoff_t pgoff;
          struct page **pages;
  
          /*
           * special mappings have no vm_file, and in that case, the mm
           * uses vm_pgoff internally. So we have to subtract it from here.
           * We are allowed to do this because we are the mm; do not copy
           * this code into drivers!
           */
          pgoff = vmf->pgoff - vma->vm_pgoff;
  
          for (pages = vma->vm_private_data; pgoff && *pages; ++pages)
                  pgoff--;
  
          if (*pages) {
                  struct page *page = *pages;
                  get_page(page);
                  vmf->page = page;
                  return 0;
          }
  
          return VM_FAULT_SIGBUS;
  }
  
  /*
   * Having a close hook prevents vma merging regardless of flags.
   */
  static void special_mapping_close(struct vm_area_struct *vma)
  {
  }
  
  static const struct vm_operations_struct special_mapping_vmops = {
          .close = special_mapping_close,
          .fault = special_mapping_fault,
  };
  
  /*
   * Called with mm->mmap_sem held for writing.
   * Insert a new vma covering the given region, with the given flags.
   * Its pages are supplied by the given array of struct page *.
   * The array can be shorter than len >> PAGE_SHIFT if it's null-terminated.
   * The region past the last page supplied will always produce SIGBUS.
   * The array pointer and the pages it points to are assumed to stay alive
   * for as long as this mapping might exist.
   */
  int install_special_mapping(struct mm_struct *mm,
                              unsigned long addr, unsigned long len,
                              unsigned long vm_flags, struct page **pages)
  {
          int ret;
          struct vm_area_struct *vma;
  
          vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
          if (unlikely(vma == NULL))
                  return -ENOMEM;
  
          INIT_LIST_HEAD(&vma->anon_vma_chain);
          vma->vm_mm = mm;
          vma->vm_start = addr;
          vma->vm_end = addr + len;
  
          vma->vm_flags = vm_flags | mm->def_flags | VM_DONTEXPAND;
          vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
  
          vma->vm_ops = &special_mapping_vmops;
          vma->vm_private_data = pages;
  
          ret = insert_vm_struct(mm, vma);
          if (ret)
                  goto out;
  
          mm->total_vm += len >> PAGE_SHIFT;
  
          perf_event_mmap(vma);
  
          return 0;
  
  out:
          kmem_cache_free(vm_area_cachep, vma);
          return ret;
  }
  
  static DEFINE_MUTEX(mm_all_locks_mutex);
  
  static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)
  {
          if (!test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_node)) {
                  /*
                   * The LSB of head.next can't change from under us
                   * because we hold the mm_all_locks_mutex.
                   */
                  down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_sem);
                  /*
                   * We can safely modify head.next after taking the
                   * anon_vma->root->rwsem. If some other vma in this mm shares
                   * the same anon_vma we won't take it again.
                   *
                   * No need of atomic instructions here, head.next
                   * can't change from under us thanks to the
                   * anon_vma->root->rwsem.
                   */
                  if (__test_and_set_bit(0, (unsigned long *)
                                         &anon_vma->root->rb_root.rb_node))
                          BUG();
          }
  }
  
  static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
  {
          if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
                  /*
                   * AS_MM_ALL_LOCKS can't change from under us because
                   * we hold the mm_all_locks_mutex.
                   *
                   * Operations on ->flags have to be atomic because
                   * even if AS_MM_ALL_LOCKS is stable thanks to the
                   * mm_all_locks_mutex, there may be other cpus
                   * changing other bitflags in parallel to us.
                   */
                  if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
                          BUG();
                  mutex_lock_nest_lock(&mapping->i_mmap_mutex, &mm->mmap_sem);
          }
  }
  
  /*
   * This operation locks against the VM for all pte/vma/mm related
   * operations that could ever happen on a certain mm. This includes
   * vmtruncate, try_to_unmap, and all page faults.
   *
   * The caller must take the mmap_sem in write mode before calling
   * mm_take_all_locks(). The caller isn't allowed to release the
   * mmap_sem until mm_drop_all_locks() returns.
   *
   * mmap_sem in write mode is required in order to block all operations
   * that could modify pagetables and free pages without need of
   * altering the vma layout (for example populate_range() with
   * nonlinear vmas). It's also needed in write mode to avoid new
   * anon_vmas to be associated with existing vmas.
   *
   * A single task can't take more than one mm_take_all_locks() in a row
   * or it would deadlock.
   *
   * The LSB in anon_vma->rb_root.rb_node and the AS_MM_ALL_LOCKS bitflag in
   * mapping->flags avoid to take the same lock twice, if more than one
   * vma in this mm is backed by the same anon_vma or address_space.
   *
   * We can take all the locks in random order because the VM code
   * taking i_mmap_mutex or anon_vma->mutex outside the mmap_sem never
   * takes more than one of them in a row. Secondly we're protected
   * against a concurrent mm_take_all_locks() by the mm_all_locks_mutex.
   *
   * mm_take_all_locks() and mm_drop_all_locks are expensive operations
   * that may have to take thousand of locks.
   *
   * mm_take_all_locks() can fail if it's interrupted by signals.
   */
  int mm_take_all_locks(struct mm_struct *mm)
  {
          struct vm_area_struct *vma;
          struct anon_vma_chain *avc;
  
          BUG_ON(down_read_trylock(&mm->mmap_sem));
  
          mutex_lock(&mm_all_locks_mutex);
  
          for (vma = mm->mmap; vma; vma = vma->vm_next) {
                  if (signal_pending(current))
                          goto out_unlock;
                  if (vma->vm_file && vma->vm_file->f_mapping)
                          vm_lock_mapping(mm, vma->vm_file->f_mapping);
          }
  
          for (vma = mm->mmap; vma; vma = vma->vm_next) {
                  if (signal_pending(current))
                          goto out_unlock;
                  if (vma->anon_vma)
                          list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                                  vm_lock_anon_vma(mm, avc->anon_vma);
          }
  
          return 0;
  
  out_unlock:
          mm_drop_all_locks(mm);
          return -EINTR;
  }
  
  static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
  {
          if (test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_node)) {
                  /*
                   * The LSB of head.next can't change to 0 from under
                   * us because we hold the mm_all_locks_mutex.
                   *
                   * We must however clear the bitflag before unlocking
                   * the vma so the users using the anon_vma->rb_root will
                   * never see our bitflag.
                   *
                   * No need of atomic instructions here, head.next
                   * can't change from under us until we release the
                   * anon_vma->root->rwsem.
                   */
                  if (!__test_and_clear_bit(0, (unsigned long *)
                                            &anon_vma->root->rb_root.rb_node))
                          BUG();
                  anon_vma_unlock(anon_vma);
          }
  }
  
  static void vm_unlock_mapping(struct address_space *mapping)
  {
          if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
                  /*
                   * AS_MM_ALL_LOCKS can't change to 0 from under us
                   * because we hold the mm_all_locks_mutex.
                   */
                  mutex_unlock(&mapping->i_mmap_mutex);
                  if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
                                          &mapping->flags))
                          BUG();
          }
  }
  
  /*
   * The mmap_sem cannot be released by the caller until
   * mm_drop_all_locks() returns.
   */
  void mm_drop_all_locks(struct mm_struct *mm)
  {
          struct vm_area_struct *vma;
          struct anon_vma_chain *avc;
  
          BUG_ON(down_read_trylock(&mm->mmap_sem));
          BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
  
          for (vma = mm->mmap; vma; vma = vma->vm_next) {
                  if (vma->anon_vma)
                          list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                                  vm_unlock_anon_vma(avc->anon_vma);
                  if (vma->vm_file && vma->vm_file->f_mapping)
                          vm_unlock_mapping(vma->vm_file->f_mapping);
          }
  
          mutex_unlock(&mm_all_locks_mutex);
  }
  
  /*
   * initialise the VMA slab
   */
  void __init mmap_init(void)
  {
          int ret;
  
          ret = percpu_counter_init(&vm_committed_as, 0);
          VM_BUG_ON(ret);
  }

Cache object: 9cd07c3c83d57537e2e7f12afa04420a