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

     /*
      *      linux/mm/mlock.c
      *
      *  (C) Copyright 1995 Linus Torvalds
      *  (C) Copyright 2002 Christoph Hellwig
      */
     
     #include <linux/capability.h>
     #include <linux/mman.h>
    #include <linux/mm.h>
    #include <linux/swap.h>
    #include <linux/swapops.h>
    #include <linux/pagemap.h>
    #include <linux/mempolicy.h>
    #include <linux/syscalls.h>
    #include <linux/sched.h>
    #include <linux/export.h>
    #include <linux/rmap.h>
    #include <linux/mmzone.h>
    #include <linux/hugetlb.h>
    
    #include "internal.h"
    
    int can_do_mlock(void)
    {
            if (capable(CAP_IPC_LOCK))
                    return 1;
            if (rlimit(RLIMIT_MEMLOCK) != 0)
                    return 1;
            return 0;
    }
    EXPORT_SYMBOL(can_do_mlock);
    
    /*
     * Mlocked pages are marked with PageMlocked() flag for efficient testing
     * in vmscan and, possibly, the fault path; and to support semi-accurate
     * statistics.
     *
     * An mlocked page [PageMlocked(page)] is unevictable.  As such, it will
     * be placed on the LRU "unevictable" list, rather than the [in]active lists.
     * The unevictable list is an LRU sibling list to the [in]active lists.
     * PageUnevictable is set to indicate the unevictable state.
     *
     * When lazy mlocking via vmscan, it is important to ensure that the
     * vma's VM_LOCKED status is not concurrently being modified, otherwise we
     * may have mlocked a page that is being munlocked. So lazy mlock must take
     * the mmap_sem for read, and verify that the vma really is locked
     * (see mm/rmap.c).
     */
    
    /*
     *  LRU accounting for clear_page_mlock()
     */
    void clear_page_mlock(struct page *page)
    {
            if (!TestClearPageMlocked(page))
                    return;
    
            mod_zone_page_state(page_zone(page), NR_MLOCK,
                                -hpage_nr_pages(page));
            count_vm_event(UNEVICTABLE_PGCLEARED);
            if (!isolate_lru_page(page)) {
                    putback_lru_page(page);
            } else {
                    /*
                     * We lost the race. the page already moved to evictable list.
                     */
                    if (PageUnevictable(page))
                            count_vm_event(UNEVICTABLE_PGSTRANDED);
            }
    }
    
    /*
     * Mark page as mlocked if not already.
     * If page on LRU, isolate and putback to move to unevictable list.
     */
    void mlock_vma_page(struct page *page)
    {
            BUG_ON(!PageLocked(page));
    
            if (!TestSetPageMlocked(page)) {
                    mod_zone_page_state(page_zone(page), NR_MLOCK,
                                        hpage_nr_pages(page));
                    count_vm_event(UNEVICTABLE_PGMLOCKED);
                    if (!isolate_lru_page(page))
                            putback_lru_page(page);
            }
    }
    
    /**
     * munlock_vma_page - munlock a vma page
     * @page - page to be unlocked
     *
     * called from munlock()/munmap() path with page supposedly on the LRU.
     * When we munlock a page, because the vma where we found the page is being
     * munlock()ed or munmap()ed, we want to check whether other vmas hold the
     * page locked so that we can leave it on the unevictable lru list and not
     * bother vmscan with it.  However, to walk the page's rmap list in
     * try_to_munlock() we must isolate the page from the LRU.  If some other
    * task has removed the page from the LRU, we won't be able to do that.
    * So we clear the PageMlocked as we might not get another chance.  If we
    * can't isolate the page, we leave it for putback_lru_page() and vmscan
    * [page_referenced()/try_to_unmap()] to deal with.
    */
   void munlock_vma_page(struct page *page)
   {
           BUG_ON(!PageLocked(page));
   
           if (TestClearPageMlocked(page)) {
                   mod_zone_page_state(page_zone(page), NR_MLOCK,
                                       -hpage_nr_pages(page));
                   if (!isolate_lru_page(page)) {
                           int ret = SWAP_AGAIN;
   
                           /*
                            * Optimization: if the page was mapped just once,
                            * that's our mapping and we don't need to check all the
                            * other vmas.
                            */
                           if (page_mapcount(page) > 1)
                                   ret = try_to_munlock(page);
                           /*
                            * did try_to_unlock() succeed or punt?
                            */
                           if (ret != SWAP_MLOCK)
                                   count_vm_event(UNEVICTABLE_PGMUNLOCKED);
   
                           putback_lru_page(page);
                   } else {
                           /*
                            * Some other task has removed the page from the LRU.
                            * putback_lru_page() will take care of removing the
                            * page from the unevictable list, if necessary.
                            * vmscan [page_referenced()] will move the page back
                            * to the unevictable list if some other vma has it
                            * mlocked.
                            */
                           if (PageUnevictable(page))
                                   count_vm_event(UNEVICTABLE_PGSTRANDED);
                           else
                                   count_vm_event(UNEVICTABLE_PGMUNLOCKED);
                   }
           }
   }
   
   /**
    * __mlock_vma_pages_range() -  mlock a range of pages in the vma.
    * @vma:   target vma
    * @start: start address
    * @end:   end address
    *
    * This takes care of making the pages present too.
    *
    * return 0 on success, negative error code on error.
    *
    * vma->vm_mm->mmap_sem must be held for at least read.
    */
   static long __mlock_vma_pages_range(struct vm_area_struct *vma,
                                       unsigned long start, unsigned long end,
                                       int *nonblocking)
   {
           struct mm_struct *mm = vma->vm_mm;
           unsigned long addr = start;
           int nr_pages = (end - start) / PAGE_SIZE;
           int gup_flags;
   
           VM_BUG_ON(start & ~PAGE_MASK);
           VM_BUG_ON(end   & ~PAGE_MASK);
           VM_BUG_ON(start < vma->vm_start);
           VM_BUG_ON(end   > vma->vm_end);
           VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
   
           gup_flags = FOLL_TOUCH | FOLL_MLOCK;
           /*
            * We want to touch writable mappings with a write fault in order
            * to break COW, except for shared mappings because these don't COW
            * and we would not want to dirty them for nothing.
            */
           if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
                   gup_flags |= FOLL_WRITE;
   
           /*
            * We want mlock to succeed for regions that have any permissions
            * other than PROT_NONE.
            */
           if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
                   gup_flags |= FOLL_FORCE;
   
           return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
                                   NULL, NULL, nonblocking);
   }
   
   /*
    * convert get_user_pages() return value to posix mlock() error
    */
   static int __mlock_posix_error_return(long retval)
   {
           if (retval == -EFAULT)
                   retval = -ENOMEM;
           else if (retval == -ENOMEM)
                   retval = -EAGAIN;
           return retval;
   }
   
   /**
    * mlock_vma_pages_range() - mlock pages in specified vma range.
    * @vma - the vma containing the specfied address range
    * @start - starting address in @vma to mlock
    * @end   - end address [+1] in @vma to mlock
    *
    * For mmap()/mremap()/expansion of mlocked vma.
    *
    * return 0 on success for "normal" vmas.
    *
    * return number of pages [> 0] to be removed from locked_vm on success
    * of "special" vmas.
    */
   long mlock_vma_pages_range(struct vm_area_struct *vma,
                           unsigned long start, unsigned long end)
   {
           int nr_pages = (end - start) / PAGE_SIZE;
           BUG_ON(!(vma->vm_flags & VM_LOCKED));
   
           /*
            * filter unlockable vmas
            */
           if (vma->vm_flags & (VM_IO | VM_PFNMAP))
                   goto no_mlock;
   
           if (!((vma->vm_flags & VM_DONTEXPAND) ||
                           is_vm_hugetlb_page(vma) ||
                           vma == get_gate_vma(current->mm))) {
   
                   __mlock_vma_pages_range(vma, start, end, NULL);
   
                   /* Hide errors from mmap() and other callers */
                   return 0;
           }
   
           /*
            * User mapped kernel pages or huge pages:
            * make these pages present to populate the ptes, but
            * fall thru' to reset VM_LOCKED--no need to unlock, and
            * return nr_pages so these don't get counted against task's
            * locked limit.  huge pages are already counted against
            * locked vm limit.
            */
           make_pages_present(start, end);
   
   no_mlock:
           vma->vm_flags &= ~VM_LOCKED;    /* and don't come back! */
           return nr_pages;                /* error or pages NOT mlocked */
   }
   
   /*
    * munlock_vma_pages_range() - munlock all pages in the vma range.'
    * @vma - vma containing range to be munlock()ed.
    * @start - start address in @vma of the range
    * @end - end of range in @vma.
    *
    *  For mremap(), munmap() and exit().
    *
    * Called with @vma VM_LOCKED.
    *
    * Returns with VM_LOCKED cleared.  Callers must be prepared to
    * deal with this.
    *
    * We don't save and restore VM_LOCKED here because pages are
    * still on lru.  In unmap path, pages might be scanned by reclaim
    * and re-mlocked by try_to_{munlock|unmap} before we unmap and
    * free them.  This will result in freeing mlocked pages.
    */
   void munlock_vma_pages_range(struct vm_area_struct *vma,
                                unsigned long start, unsigned long end)
   {
           unsigned long addr;
   
           lru_add_drain();
           vma->vm_flags &= ~VM_LOCKED;
   
           for (addr = start; addr < end; addr += PAGE_SIZE) {
                   struct page *page;
                   /*
                    * Although FOLL_DUMP is intended for get_dump_page(),
                    * it just so happens that its special treatment of the
                    * ZERO_PAGE (returning an error instead of doing get_page)
                    * suits munlock very well (and if somehow an abnormal page
                    * has sneaked into the range, we won't oops here: great).
                    */
                   page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
                   if (page && !IS_ERR(page)) {
                           lock_page(page);
                           munlock_vma_page(page);
                           unlock_page(page);
                           put_page(page);
                   }
                   cond_resched();
           }
   }
   
   /*
    * mlock_fixup  - handle mlock[all]/munlock[all] requests.
    *
    * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
    * munlock is a no-op.  However, for some special vmas, we go ahead and
    * populate the ptes via make_pages_present().
    *
    * For vmas that pass the filters, merge/split as appropriate.
    */
   static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
           unsigned long start, unsigned long end, vm_flags_t newflags)
   {
           struct mm_struct *mm = vma->vm_mm;
           pgoff_t pgoff;
           int nr_pages;
           int ret = 0;
           int lock = !!(newflags & VM_LOCKED);
   
           if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
               is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
                   goto out;       /* don't set VM_LOCKED,  don't count */
   
           pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
           *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
                             vma->vm_file, pgoff, vma_policy(vma));
           if (*prev) {
                   vma = *prev;
                   goto success;
           }
   
           if (start != vma->vm_start) {
                   ret = split_vma(mm, vma, start, 1);
                   if (ret)
                           goto out;
           }
   
           if (end != vma->vm_end) {
                   ret = split_vma(mm, vma, end, 0);
                   if (ret)
                           goto out;
           }
   
   success:
           /*
            * Keep track of amount of locked VM.
            */
           nr_pages = (end - start) >> PAGE_SHIFT;
           if (!lock)
                   nr_pages = -nr_pages;
           mm->locked_vm += nr_pages;
   
           /*
            * vm_flags is protected by the mmap_sem held in write mode.
            * It's okay if try_to_unmap_one unmaps a page just after we
            * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
            */
   
           if (lock)
                   vma->vm_flags = newflags;
           else
                   munlock_vma_pages_range(vma, start, end);
   
   out:
           *prev = vma;
           return ret;
   }
   
   static int do_mlock(unsigned long start, size_t len, int on)
   {
           unsigned long nstart, end, tmp;
           struct vm_area_struct * vma, * prev;
           int error;
   
           VM_BUG_ON(start & ~PAGE_MASK);
           VM_BUG_ON(len != PAGE_ALIGN(len));
           end = start + len;
           if (end < start)
                   return -EINVAL;
           if (end == start)
                   return 0;
           vma = find_vma(current->mm, start);
           if (!vma || vma->vm_start > start)
                   return -ENOMEM;
   
           prev = vma->vm_prev;
           if (start > vma->vm_start)
                   prev = vma;
   
           for (nstart = start ; ; ) {
                   vm_flags_t newflags;
   
                   /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
   
                   newflags = vma->vm_flags | VM_LOCKED;
                   if (!on)
                           newflags &= ~VM_LOCKED;
   
                   tmp = vma->vm_end;
                   if (tmp > end)
                           tmp = end;
                   error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
                   if (error)
                           break;
                   nstart = tmp;
                   if (nstart < prev->vm_end)
                           nstart = prev->vm_end;
                   if (nstart >= end)
                           break;
   
                   vma = prev->vm_next;
                   if (!vma || vma->vm_start != nstart) {
                           error = -ENOMEM;
                           break;
                   }
           }
           return error;
   }
   
   static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors)
   {
           struct mm_struct *mm = current->mm;
           unsigned long end, nstart, nend;
           struct vm_area_struct *vma = NULL;
           int locked = 0;
           int ret = 0;
   
           VM_BUG_ON(start & ~PAGE_MASK);
           VM_BUG_ON(len != PAGE_ALIGN(len));
           end = start + len;
   
           for (nstart = start; nstart < end; nstart = nend) {
                   /*
                    * We want to fault in pages for [nstart; end) address range.
                    * Find first corresponding VMA.
                    */
                   if (!locked) {
                           locked = 1;
                           down_read(&mm->mmap_sem);
                           vma = find_vma(mm, nstart);
                   } else if (nstart >= vma->vm_end)
                           vma = vma->vm_next;
                   if (!vma || vma->vm_start >= end)
                           break;
                   /*
                    * Set [nstart; nend) to intersection of desired address
                    * range with the first VMA. Also, skip undesirable VMA types.
                    */
                   nend = min(end, vma->vm_end);
                   if (vma->vm_flags & (VM_IO | VM_PFNMAP))
                           continue;
                   if (nstart < vma->vm_start)
                           nstart = vma->vm_start;
                   /*
                    * Now fault in a range of pages. __mlock_vma_pages_range()
                    * double checks the vma flags, so that it won't mlock pages
                    * if the vma was already munlocked.
                    */
                   ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
                   if (ret < 0) {
                           if (ignore_errors) {
                                   ret = 0;
                                   continue;       /* continue at next VMA */
                           }
                           ret = __mlock_posix_error_return(ret);
                           break;
                   }
                   nend = nstart + ret * PAGE_SIZE;
                   ret = 0;
           }
           if (locked)
                   up_read(&mm->mmap_sem);
           return ret;     /* 0 or negative error code */
   }
   
   SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
   {
           unsigned long locked;
           unsigned long lock_limit;
           int error = -ENOMEM;
   
           if (!can_do_mlock())
                   return -EPERM;
   
           lru_add_drain_all();    /* flush pagevec */
   
           down_write(&current->mm->mmap_sem);
           len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
           start &= PAGE_MASK;
   
           locked = len >> PAGE_SHIFT;
           locked += current->mm->locked_vm;
   
           lock_limit = rlimit(RLIMIT_MEMLOCK);
           lock_limit >>= PAGE_SHIFT;
   
           /* check against resource limits */
           if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
                   error = do_mlock(start, len, 1);
           up_write(&current->mm->mmap_sem);
           if (!error)
                   error = do_mlock_pages(start, len, 0);
           return error;
   }
   
   SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
   {
           int ret;
   
           down_write(&current->mm->mmap_sem);
           len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
           start &= PAGE_MASK;
           ret = do_mlock(start, len, 0);
           up_write(&current->mm->mmap_sem);
           return ret;
   }
   
   static int do_mlockall(int flags)
   {
           struct vm_area_struct * vma, * prev = NULL;
           unsigned int def_flags = 0;
   
           if (flags & MCL_FUTURE)
                   def_flags = VM_LOCKED;
           current->mm->def_flags = def_flags;
           if (flags == MCL_FUTURE)
                   goto out;
   
           for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
                   vm_flags_t newflags;
   
                   newflags = vma->vm_flags | VM_LOCKED;
                   if (!(flags & MCL_CURRENT))
                           newflags &= ~VM_LOCKED;
   
                   /* Ignore errors */
                   mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
           }
   out:
           return 0;
   }
   
   SYSCALL_DEFINE1(mlockall, int, flags)
   {
           unsigned long lock_limit;
           int ret = -EINVAL;
   
           if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
                   goto out;
   
           ret = -EPERM;
           if (!can_do_mlock())
                   goto out;
   
           if (flags & MCL_CURRENT)
                   lru_add_drain_all();    /* flush pagevec */
   
           down_write(&current->mm->mmap_sem);
   
           lock_limit = rlimit(RLIMIT_MEMLOCK);
           lock_limit >>= PAGE_SHIFT;
   
           ret = -ENOMEM;
           if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
               capable(CAP_IPC_LOCK))
                   ret = do_mlockall(flags);
           up_write(&current->mm->mmap_sem);
           if (!ret && (flags & MCL_CURRENT)) {
                   /* Ignore errors */
                   do_mlock_pages(0, TASK_SIZE, 1);
           }
   out:
           return ret;
   }
   
   SYSCALL_DEFINE0(munlockall)
   {
           int ret;
   
           down_write(&current->mm->mmap_sem);
           ret = do_mlockall(0);
           up_write(&current->mm->mmap_sem);
           return ret;
   }
   
   /*
    * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
    * shm segments) get accounted against the user_struct instead.
    */
   static DEFINE_SPINLOCK(shmlock_user_lock);
   
   int user_shm_lock(size_t size, struct user_struct *user)
   {
           unsigned long lock_limit, locked;
           int allowed = 0;
   
           locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
           lock_limit = rlimit(RLIMIT_MEMLOCK);
           if (lock_limit == RLIM_INFINITY)
                   allowed = 1;
           lock_limit >>= PAGE_SHIFT;
           spin_lock(&shmlock_user_lock);
           if (!allowed &&
               locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
                   goto out;
           get_uid(user);
           user->locked_shm += locked;
           allowed = 1;
   out:
           spin_unlock(&shmlock_user_lock);
           return allowed;
   }
   
   void user_shm_unlock(size_t size, struct user_struct *user)
   {
           spin_lock(&shmlock_user_lock);
           user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
           spin_unlock(&shmlock_user_lock);
           free_uid(user);
   }

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