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

     /*
      * mm/kmemleak.c
      *
      * Copyright (C) 2008 ARM Limited
      * Written by Catalin Marinas <catalin.marinas@arm.com>
      *
      * This program is free software; you can redistribute it and/or modify
      * it under the terms of the GNU General Public License version 2 as
      * published by the Free Software Foundation.
     *
     * This program is distributed in the hope that it will be useful,
     * but WITHOUT ANY WARRANTY; without even the implied warranty of
     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     * GNU General Public License for more details.
     *
     * You should have received a copy of the GNU General Public License
     * along with this program; if not, write to the Free Software
     * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
     *
     *
     * For more information on the algorithm and kmemleak usage, please see
     * Documentation/kmemleak.txt.
     *
     * Notes on locking
     * ----------------
     *
     * The following locks and mutexes are used by kmemleak:
     *
     * - kmemleak_lock (rwlock): protects the object_list modifications and
     *   accesses to the object_tree_root. The object_list is the main list
     *   holding the metadata (struct kmemleak_object) for the allocated memory
     *   blocks. The object_tree_root is a red black tree used to look-up
     *   metadata based on a pointer to the corresponding memory block.  The
     *   kmemleak_object structures are added to the object_list and
     *   object_tree_root in the create_object() function called from the
     *   kmemleak_alloc() callback and removed in delete_object() called from the
     *   kmemleak_free() callback
     * - kmemleak_object.lock (spinlock): protects a kmemleak_object. Accesses to
     *   the metadata (e.g. count) are protected by this lock. Note that some
     *   members of this structure may be protected by other means (atomic or
     *   kmemleak_lock). This lock is also held when scanning the corresponding
     *   memory block to avoid the kernel freeing it via the kmemleak_free()
     *   callback. This is less heavyweight than holding a global lock like
     *   kmemleak_lock during scanning
     * - scan_mutex (mutex): ensures that only one thread may scan the memory for
     *   unreferenced objects at a time. The gray_list contains the objects which
     *   are already referenced or marked as false positives and need to be
     *   scanned. This list is only modified during a scanning episode when the
     *   scan_mutex is held. At the end of a scan, the gray_list is always empty.
     *   Note that the kmemleak_object.use_count is incremented when an object is
     *   added to the gray_list and therefore cannot be freed. This mutex also
     *   prevents multiple users of the "kmemleak" debugfs file together with
     *   modifications to the memory scanning parameters including the scan_thread
     *   pointer
     *
     * The kmemleak_object structures have a use_count incremented or decremented
     * using the get_object()/put_object() functions. When the use_count becomes
     * 0, this count can no longer be incremented and put_object() schedules the
     * kmemleak_object freeing via an RCU callback. All calls to the get_object()
     * function must be protected by rcu_read_lock() to avoid accessing a freed
     * structure.
     */
    
    #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
    
    #include <linux/init.h>
    #include <linux/kernel.h>
    #include <linux/list.h>
    #include <linux/sched.h>
    #include <linux/jiffies.h>
    #include <linux/delay.h>
    #include <linux/export.h>
    #include <linux/kthread.h>
    #include <linux/rbtree.h>
    #include <linux/fs.h>
    #include <linux/debugfs.h>
    #include <linux/seq_file.h>
    #include <linux/cpumask.h>
    #include <linux/spinlock.h>
    #include <linux/mutex.h>
    #include <linux/rcupdate.h>
    #include <linux/stacktrace.h>
    #include <linux/cache.h>
    #include <linux/percpu.h>
    #include <linux/hardirq.h>
    #include <linux/mmzone.h>
    #include <linux/slab.h>
    #include <linux/thread_info.h>
    #include <linux/err.h>
    #include <linux/uaccess.h>
    #include <linux/string.h>
    #include <linux/nodemask.h>
    #include <linux/mm.h>
    #include <linux/workqueue.h>
    #include <linux/crc32.h>
    
    #include <asm/sections.h>
    #include <asm/processor.h>
    #include <linux/atomic.h>
   
   #include <linux/kmemcheck.h>
   #include <linux/kmemleak.h>
   #include <linux/memory_hotplug.h>
   
   /*
    * Kmemleak configuration and common defines.
    */
   #define MAX_TRACE               16      /* stack trace length */
   #define MSECS_MIN_AGE           5000    /* minimum object age for reporting */
   #define SECS_FIRST_SCAN         60      /* delay before the first scan */
   #define SECS_SCAN_WAIT          600     /* subsequent auto scanning delay */
   #define MAX_SCAN_SIZE           4096    /* maximum size of a scanned block */
   
   #define BYTES_PER_POINTER       sizeof(void *)
   
   /* GFP bitmask for kmemleak internal allocations */
   #define gfp_kmemleak_mask(gfp)  (((gfp) & (GFP_KERNEL | GFP_ATOMIC)) | \
                                    __GFP_NORETRY | __GFP_NOMEMALLOC | \
                                    __GFP_NOWARN)
   
   /* scanning area inside a memory block */
   struct kmemleak_scan_area {
           struct hlist_node node;
           unsigned long start;
           size_t size;
   };
   
   #define KMEMLEAK_GREY   0
   #define KMEMLEAK_BLACK  -1
   
   /*
    * Structure holding the metadata for each allocated memory block.
    * Modifications to such objects should be made while holding the
    * object->lock. Insertions or deletions from object_list, gray_list or
    * rb_node are already protected by the corresponding locks or mutex (see
    * the notes on locking above). These objects are reference-counted
    * (use_count) and freed using the RCU mechanism.
    */
   struct kmemleak_object {
           spinlock_t lock;
           unsigned long flags;            /* object status flags */
           struct list_head object_list;
           struct list_head gray_list;
           struct rb_node rb_node;
           struct rcu_head rcu;            /* object_list lockless traversal */
           /* object usage count; object freed when use_count == 0 */
           atomic_t use_count;
           unsigned long pointer;
           size_t size;
           /* minimum number of a pointers found before it is considered leak */
           int min_count;
           /* the total number of pointers found pointing to this object */
           int count;
           /* checksum for detecting modified objects */
           u32 checksum;
           /* memory ranges to be scanned inside an object (empty for all) */
           struct hlist_head area_list;
           unsigned long trace[MAX_TRACE];
           unsigned int trace_len;
           unsigned long jiffies;          /* creation timestamp */
           pid_t pid;                      /* pid of the current task */
           char comm[TASK_COMM_LEN];       /* executable name */
   };
   
   /* flag representing the memory block allocation status */
   #define OBJECT_ALLOCATED        (1 << 0)
   /* flag set after the first reporting of an unreference object */
   #define OBJECT_REPORTED         (1 << 1)
   /* flag set to not scan the object */
   #define OBJECT_NO_SCAN          (1 << 2)
   
   /* number of bytes to print per line; must be 16 or 32 */
   #define HEX_ROW_SIZE            16
   /* number of bytes to print at a time (1, 2, 4, 8) */
   #define HEX_GROUP_SIZE          1
   /* include ASCII after the hex output */
   #define HEX_ASCII               1
   /* max number of lines to be printed */
   #define HEX_MAX_LINES           2
   
   /* the list of all allocated objects */
   static LIST_HEAD(object_list);
   /* the list of gray-colored objects (see color_gray comment below) */
   static LIST_HEAD(gray_list);
   /* search tree for object boundaries */
   static struct rb_root object_tree_root = RB_ROOT;
   /* rw_lock protecting the access to object_list and object_tree_root */
   static DEFINE_RWLOCK(kmemleak_lock);
   
   /* allocation caches for kmemleak internal data */
   static struct kmem_cache *object_cache;
   static struct kmem_cache *scan_area_cache;
   
   /* set if tracing memory operations is enabled */
   static atomic_t kmemleak_enabled = ATOMIC_INIT(0);
   /* set in the late_initcall if there were no errors */
   static atomic_t kmemleak_initialized = ATOMIC_INIT(0);
   /* enables or disables early logging of the memory operations */
   static atomic_t kmemleak_early_log = ATOMIC_INIT(1);
   /* set if a kmemleak warning was issued */
   static atomic_t kmemleak_warning = ATOMIC_INIT(0);
   /* set if a fatal kmemleak error has occurred */
   static atomic_t kmemleak_error = ATOMIC_INIT(0);
   
   /* minimum and maximum address that may be valid pointers */
   static unsigned long min_addr = ULONG_MAX;
   static unsigned long max_addr;
   
   static struct task_struct *scan_thread;
   /* used to avoid reporting of recently allocated objects */
   static unsigned long jiffies_min_age;
   static unsigned long jiffies_last_scan;
   /* delay between automatic memory scannings */
   static signed long jiffies_scan_wait;
   /* enables or disables the task stacks scanning */
   static int kmemleak_stack_scan = 1;
   /* protects the memory scanning, parameters and debug/kmemleak file access */
   static DEFINE_MUTEX(scan_mutex);
   /* setting kmemleak=on, will set this var, skipping the disable */
   static int kmemleak_skip_disable;
   
   
   /*
    * Early object allocation/freeing logging. Kmemleak is initialized after the
    * kernel allocator. However, both the kernel allocator and kmemleak may
    * allocate memory blocks which need to be tracked. Kmemleak defines an
    * arbitrary buffer to hold the allocation/freeing information before it is
    * fully initialized.
    */
   
   /* kmemleak operation type for early logging */
   enum {
           KMEMLEAK_ALLOC,
           KMEMLEAK_ALLOC_PERCPU,
           KMEMLEAK_FREE,
           KMEMLEAK_FREE_PART,
           KMEMLEAK_FREE_PERCPU,
           KMEMLEAK_NOT_LEAK,
           KMEMLEAK_IGNORE,
           KMEMLEAK_SCAN_AREA,
           KMEMLEAK_NO_SCAN
   };
   
   /*
    * Structure holding the information passed to kmemleak callbacks during the
    * early logging.
    */
   struct early_log {
           int op_type;                    /* kmemleak operation type */
           const void *ptr;                /* allocated/freed memory block */
           size_t size;                    /* memory block size */
           int min_count;                  /* minimum reference count */
           unsigned long trace[MAX_TRACE]; /* stack trace */
           unsigned int trace_len;         /* stack trace length */
   };
   
   /* early logging buffer and current position */
   static struct early_log
           early_log[CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE] __initdata;
   static int crt_early_log __initdata;
   
   static void kmemleak_disable(void);
   
   /*
    * Print a warning and dump the stack trace.
    */
   #define kmemleak_warn(x...)     do {            \
           pr_warning(x);                          \
           dump_stack();                           \
           atomic_set(&kmemleak_warning, 1);       \
   } while (0)
   
   /*
    * Macro invoked when a serious kmemleak condition occurred and cannot be
    * recovered from. Kmemleak will be disabled and further allocation/freeing
    * tracing no longer available.
    */
   #define kmemleak_stop(x...)     do {    \
           kmemleak_warn(x);               \
           kmemleak_disable();             \
   } while (0)
   
   /*
    * Printing of the objects hex dump to the seq file. The number of lines to be
    * printed is limited to HEX_MAX_LINES to prevent seq file spamming. The
    * actual number of printed bytes depends on HEX_ROW_SIZE. It must be called
    * with the object->lock held.
    */
   static void hex_dump_object(struct seq_file *seq,
                               struct kmemleak_object *object)
   {
           const u8 *ptr = (const u8 *)object->pointer;
           int i, len, remaining;
           unsigned char linebuf[HEX_ROW_SIZE * 5];
   
           /* limit the number of lines to HEX_MAX_LINES */
           remaining = len =
                   min(object->size, (size_t)(HEX_MAX_LINES * HEX_ROW_SIZE));
   
           seq_printf(seq, "  hex dump (first %d bytes):\n", len);
           for (i = 0; i < len; i += HEX_ROW_SIZE) {
                   int linelen = min(remaining, HEX_ROW_SIZE);
   
                   remaining -= HEX_ROW_SIZE;
                   hex_dump_to_buffer(ptr + i, linelen, HEX_ROW_SIZE,
                                      HEX_GROUP_SIZE, linebuf, sizeof(linebuf),
                                      HEX_ASCII);
                   seq_printf(seq, "    %s\n", linebuf);
           }
   }
   
   /*
    * Object colors, encoded with count and min_count:
    * - white - orphan object, not enough references to it (count < min_count)
    * - gray  - not orphan, not marked as false positive (min_count == 0) or
    *              sufficient references to it (count >= min_count)
    * - black - ignore, it doesn't contain references (e.g. text section)
    *              (min_count == -1). No function defined for this color.
    * Newly created objects don't have any color assigned (object->count == -1)
    * before the next memory scan when they become white.
    */
   static bool color_white(const struct kmemleak_object *object)
   {
           return object->count != KMEMLEAK_BLACK &&
                   object->count < object->min_count;
   }
   
   static bool color_gray(const struct kmemleak_object *object)
   {
           return object->min_count != KMEMLEAK_BLACK &&
                   object->count >= object->min_count;
   }
   
   /*
    * Objects are considered unreferenced only if their color is white, they have
    * not be deleted and have a minimum age to avoid false positives caused by
    * pointers temporarily stored in CPU registers.
    */
   static bool unreferenced_object(struct kmemleak_object *object)
   {
           return (color_white(object) && object->flags & OBJECT_ALLOCATED) &&
                   time_before_eq(object->jiffies + jiffies_min_age,
                                  jiffies_last_scan);
   }
   
   /*
    * Printing of the unreferenced objects information to the seq file. The
    * print_unreferenced function must be called with the object->lock held.
    */
   static void print_unreferenced(struct seq_file *seq,
                                  struct kmemleak_object *object)
   {
           int i;
           unsigned int msecs_age = jiffies_to_msecs(jiffies - object->jiffies);
   
           seq_printf(seq, "unreferenced object 0x%08lx (size %zu):\n",
                      object->pointer, object->size);
           seq_printf(seq, "  comm \"%s\", pid %d, jiffies %lu (age %d.%03ds)\n",
                      object->comm, object->pid, object->jiffies,
                      msecs_age / 1000, msecs_age % 1000);
           hex_dump_object(seq, object);
           seq_printf(seq, "  backtrace:\n");
   
           for (i = 0; i < object->trace_len; i++) {
                   void *ptr = (void *)object->trace[i];
                   seq_printf(seq, "    [<%p>] %pS\n", ptr, ptr);
           }
   }
   
   /*
    * Print the kmemleak_object information. This function is used mainly for
    * debugging special cases when kmemleak operations. It must be called with
    * the object->lock held.
    */
   static void dump_object_info(struct kmemleak_object *object)
   {
           struct stack_trace trace;
   
           trace.nr_entries = object->trace_len;
           trace.entries = object->trace;
   
           pr_notice("Object 0x%08lx (size %zu):\n",
                     object->pointer, object->size);
           pr_notice("  comm \"%s\", pid %d, jiffies %lu\n",
                     object->comm, object->pid, object->jiffies);
           pr_notice("  min_count = %d\n", object->min_count);
           pr_notice("  count = %d\n", object->count);
           pr_notice("  flags = 0x%lx\n", object->flags);
           pr_notice("  checksum = %d\n", object->checksum);
           pr_notice("  backtrace:\n");
           print_stack_trace(&trace, 4);
   }
   
   /*
    * Look-up a memory block metadata (kmemleak_object) in the object search
    * tree based on a pointer value. If alias is 0, only values pointing to the
    * beginning of the memory block are allowed. The kmemleak_lock must be held
    * when calling this function.
    */
   static struct kmemleak_object *lookup_object(unsigned long ptr, int alias)
   {
           struct rb_node *rb = object_tree_root.rb_node;
   
           while (rb) {
                   struct kmemleak_object *object =
                           rb_entry(rb, struct kmemleak_object, rb_node);
                   if (ptr < object->pointer)
                           rb = object->rb_node.rb_left;
                   else if (object->pointer + object->size <= ptr)
                           rb = object->rb_node.rb_right;
                   else if (object->pointer == ptr || alias)
                           return object;
                   else {
                           kmemleak_warn("Found object by alias at 0x%08lx\n",
                                         ptr);
                           dump_object_info(object);
                           break;
                   }
           }
           return NULL;
   }
   
   /*
    * Increment the object use_count. Return 1 if successful or 0 otherwise. Note
    * that once an object's use_count reached 0, the RCU freeing was already
    * registered and the object should no longer be used. This function must be
    * called under the protection of rcu_read_lock().
    */
   static int get_object(struct kmemleak_object *object)
   {
           return atomic_inc_not_zero(&object->use_count);
   }
   
   /*
    * RCU callback to free a kmemleak_object.
    */
   static void free_object_rcu(struct rcu_head *rcu)
   {
           struct hlist_node *elem, *tmp;
           struct kmemleak_scan_area *area;
           struct kmemleak_object *object =
                   container_of(rcu, struct kmemleak_object, rcu);
   
           /*
            * Once use_count is 0 (guaranteed by put_object), there is no other
            * code accessing this object, hence no need for locking.
            */
           hlist_for_each_entry_safe(area, elem, tmp, &object->area_list, node) {
                   hlist_del(elem);
                   kmem_cache_free(scan_area_cache, area);
           }
           kmem_cache_free(object_cache, object);
   }
   
   /*
    * Decrement the object use_count. Once the count is 0, free the object using
    * an RCU callback. Since put_object() may be called via the kmemleak_free() ->
    * delete_object() path, the delayed RCU freeing ensures that there is no
    * recursive call to the kernel allocator. Lock-less RCU object_list traversal
    * is also possible.
    */
   static void put_object(struct kmemleak_object *object)
   {
           if (!atomic_dec_and_test(&object->use_count))
                   return;
   
           /* should only get here after delete_object was called */
           WARN_ON(object->flags & OBJECT_ALLOCATED);
   
           call_rcu(&object->rcu, free_object_rcu);
   }
   
   /*
    * Look up an object in the object search tree and increase its use_count.
    */
   static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias)
   {
           unsigned long flags;
           struct kmemleak_object *object = NULL;
   
           rcu_read_lock();
           read_lock_irqsave(&kmemleak_lock, flags);
           if (ptr >= min_addr && ptr < max_addr)
                   object = lookup_object(ptr, alias);
           read_unlock_irqrestore(&kmemleak_lock, flags);
   
           /* check whether the object is still available */
           if (object && !get_object(object))
                   object = NULL;
           rcu_read_unlock();
   
           return object;
   }
   
   /*
    * Save stack trace to the given array of MAX_TRACE size.
    */
   static int __save_stack_trace(unsigned long *trace)
   {
           struct stack_trace stack_trace;
   
           stack_trace.max_entries = MAX_TRACE;
           stack_trace.nr_entries = 0;
           stack_trace.entries = trace;
           stack_trace.skip = 2;
           save_stack_trace(&stack_trace);
   
           return stack_trace.nr_entries;
   }
   
   /*
    * Create the metadata (struct kmemleak_object) corresponding to an allocated
    * memory block and add it to the object_list and object_tree_root.
    */
   static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
                                                int min_count, gfp_t gfp)
   {
           unsigned long flags;
           struct kmemleak_object *object, *parent;
           struct rb_node **link, *rb_parent;
   
           object = kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp));
           if (!object) {
                   pr_warning("Cannot allocate a kmemleak_object structure\n");
                   kmemleak_disable();
                   return NULL;
           }
   
           INIT_LIST_HEAD(&object->object_list);
           INIT_LIST_HEAD(&object->gray_list);
           INIT_HLIST_HEAD(&object->area_list);
           spin_lock_init(&object->lock);
           atomic_set(&object->use_count, 1);
           object->flags = OBJECT_ALLOCATED;
           object->pointer = ptr;
           object->size = size;
           object->min_count = min_count;
           object->count = 0;                      /* white color initially */
           object->jiffies = jiffies;
           object->checksum = 0;
   
           /* task information */
           if (in_irq()) {
                   object->pid = 0;
                   strncpy(object->comm, "hardirq", sizeof(object->comm));
           } else if (in_softirq()) {
                   object->pid = 0;
                   strncpy(object->comm, "softirq", sizeof(object->comm));
           } else {
                   object->pid = current->pid;
                   /*
                    * There is a small chance of a race with set_task_comm(),
                    * however using get_task_comm() here may cause locking
                    * dependency issues with current->alloc_lock. In the worst
                    * case, the command line is not correct.
                    */
                   strncpy(object->comm, current->comm, sizeof(object->comm));
           }
   
           /* kernel backtrace */
           object->trace_len = __save_stack_trace(object->trace);
   
           write_lock_irqsave(&kmemleak_lock, flags);
   
           min_addr = min(min_addr, ptr);
           max_addr = max(max_addr, ptr + size);
           link = &object_tree_root.rb_node;
           rb_parent = NULL;
           while (*link) {
                   rb_parent = *link;
                   parent = rb_entry(rb_parent, struct kmemleak_object, rb_node);
                   if (ptr + size <= parent->pointer)
                           link = &parent->rb_node.rb_left;
                   else if (parent->pointer + parent->size <= ptr)
                           link = &parent->rb_node.rb_right;
                   else {
                           kmemleak_stop("Cannot insert 0x%lx into the object "
                                         "search tree (overlaps existing)\n",
                                         ptr);
                           kmem_cache_free(object_cache, object);
                           object = parent;
                           spin_lock(&object->lock);
                           dump_object_info(object);
                           spin_unlock(&object->lock);
                           goto out;
                   }
           }
           rb_link_node(&object->rb_node, rb_parent, link);
           rb_insert_color(&object->rb_node, &object_tree_root);
   
           list_add_tail_rcu(&object->object_list, &object_list);
   out:
           write_unlock_irqrestore(&kmemleak_lock, flags);
           return object;
   }
   
   /*
    * Remove the metadata (struct kmemleak_object) for a memory block from the
    * object_list and object_tree_root and decrement its use_count.
    */
   static void __delete_object(struct kmemleak_object *object)
   {
           unsigned long flags;
   
           write_lock_irqsave(&kmemleak_lock, flags);
           rb_erase(&object->rb_node, &object_tree_root);
           list_del_rcu(&object->object_list);
           write_unlock_irqrestore(&kmemleak_lock, flags);
   
           WARN_ON(!(object->flags & OBJECT_ALLOCATED));
           WARN_ON(atomic_read(&object->use_count) < 2);
   
           /*
            * Locking here also ensures that the corresponding memory block
            * cannot be freed when it is being scanned.
            */
           spin_lock_irqsave(&object->lock, flags);
           object->flags &= ~OBJECT_ALLOCATED;
           spin_unlock_irqrestore(&object->lock, flags);
           put_object(object);
   }
   
   /*
    * Look up the metadata (struct kmemleak_object) corresponding to ptr and
    * delete it.
    */
   static void delete_object_full(unsigned long ptr)
   {
           struct kmemleak_object *object;
   
           object = find_and_get_object(ptr, 0);
           if (!object) {
   #ifdef DEBUG
                   kmemleak_warn("Freeing unknown object at 0x%08lx\n",
                                 ptr);
   #endif
                   return;
           }
           __delete_object(object);
           put_object(object);
   }
   
   /*
    * Look up the metadata (struct kmemleak_object) corresponding to ptr and
    * delete it. If the memory block is partially freed, the function may create
    * additional metadata for the remaining parts of the block.
    */
   static void delete_object_part(unsigned long ptr, size_t size)
   {
           struct kmemleak_object *object;
           unsigned long start, end;
   
           object = find_and_get_object(ptr, 1);
           if (!object) {
   #ifdef DEBUG
                   kmemleak_warn("Partially freeing unknown object at 0x%08lx "
                                 "(size %zu)\n", ptr, size);
   #endif
                   return;
           }
           __delete_object(object);
   
           /*
            * Create one or two objects that may result from the memory block
            * split. Note that partial freeing is only done by free_bootmem() and
            * this happens before kmemleak_init() is called. The path below is
            * only executed during early log recording in kmemleak_init(), so
            * GFP_KERNEL is enough.
            */
           start = object->pointer;
           end = object->pointer + object->size;
           if (ptr > start)
                   create_object(start, ptr - start, object->min_count,
                                 GFP_KERNEL);
           if (ptr + size < end)
                   create_object(ptr + size, end - ptr - size, object->min_count,
                                 GFP_KERNEL);
   
           put_object(object);
   }
   
   static void __paint_it(struct kmemleak_object *object, int color)
   {
           object->min_count = color;
           if (color == KMEMLEAK_BLACK)
                   object->flags |= OBJECT_NO_SCAN;
   }
   
   static void paint_it(struct kmemleak_object *object, int color)
   {
           unsigned long flags;
   
           spin_lock_irqsave(&object->lock, flags);
           __paint_it(object, color);
           spin_unlock_irqrestore(&object->lock, flags);
   }
   
   static void paint_ptr(unsigned long ptr, int color)
   {
           struct kmemleak_object *object;
   
           object = find_and_get_object(ptr, 0);
           if (!object) {
                   kmemleak_warn("Trying to color unknown object "
                                 "at 0x%08lx as %s\n", ptr,
                                 (color == KMEMLEAK_GREY) ? "Grey" :
                                 (color == KMEMLEAK_BLACK) ? "Black" : "Unknown");
                   return;
           }
           paint_it(object, color);
           put_object(object);
   }
   
   /*
    * Mark an object permanently as gray-colored so that it can no longer be
    * reported as a leak. This is used in general to mark a false positive.
    */
   static void make_gray_object(unsigned long ptr)
   {
           paint_ptr(ptr, KMEMLEAK_GREY);
   }
   
   /*
    * Mark the object as black-colored so that it is ignored from scans and
    * reporting.
    */
   static void make_black_object(unsigned long ptr)
   {
           paint_ptr(ptr, KMEMLEAK_BLACK);
   }
   
   /*
    * Add a scanning area to the object. If at least one such area is added,
    * kmemleak will only scan these ranges rather than the whole memory block.
    */
   static void add_scan_area(unsigned long ptr, size_t size, gfp_t gfp)
   {
           unsigned long flags;
           struct kmemleak_object *object;
           struct kmemleak_scan_area *area;
   
           object = find_and_get_object(ptr, 1);
           if (!object) {
                   kmemleak_warn("Adding scan area to unknown object at 0x%08lx\n",
                                 ptr);
                   return;
           }
   
           area = kmem_cache_alloc(scan_area_cache, gfp_kmemleak_mask(gfp));
           if (!area) {
                   pr_warning("Cannot allocate a scan area\n");
                   goto out;
           }
   
           spin_lock_irqsave(&object->lock, flags);
           if (ptr + size > object->pointer + object->size) {
                   kmemleak_warn("Scan area larger than object 0x%08lx\n", ptr);
                   dump_object_info(object);
                   kmem_cache_free(scan_area_cache, area);
                   goto out_unlock;
           }
   
           INIT_HLIST_NODE(&area->node);
           area->start = ptr;
           area->size = size;
   
           hlist_add_head(&area->node, &object->area_list);
   out_unlock:
           spin_unlock_irqrestore(&object->lock, flags);
   out:
           put_object(object);
   }
   
   /*
    * Set the OBJECT_NO_SCAN flag for the object corresponding to the give
    * pointer. Such object will not be scanned by kmemleak but references to it
    * are searched.
    */
   static void object_no_scan(unsigned long ptr)
   {
           unsigned long flags;
           struct kmemleak_object *object;
   
           object = find_and_get_object(ptr, 0);
           if (!object) {
                   kmemleak_warn("Not scanning unknown object at 0x%08lx\n", ptr);
                   return;
           }
   
           spin_lock_irqsave(&object->lock, flags);
           object->flags |= OBJECT_NO_SCAN;
           spin_unlock_irqrestore(&object->lock, flags);
           put_object(object);
   }
   
   /*
    * Log an early kmemleak_* call to the early_log buffer. These calls will be
    * processed later once kmemleak is fully initialized.
    */
   static void __init log_early(int op_type, const void *ptr, size_t size,
                                int min_count)
   {
           unsigned long flags;
           struct early_log *log;
   
           if (atomic_read(&kmemleak_error)) {
                   /* kmemleak stopped recording, just count the requests */
                   crt_early_log++;
                   return;
           }
   
           if (crt_early_log >= ARRAY_SIZE(early_log)) {
                   kmemleak_disable();
                   return;
           }
   
           /*
            * There is no need for locking since the kernel is still in UP mode
            * at this stage. Disabling the IRQs is enough.
            */
           local_irq_save(flags);
           log = &early_log[crt_early_log];
           log->op_type = op_type;
           log->ptr = ptr;
           log->size = size;
           log->min_count = min_count;
           log->trace_len = __save_stack_trace(log->trace);
           crt_early_log++;
           local_irq_restore(flags);
   }
   
   /*
    * Log an early allocated block and populate the stack trace.
    */
   static void early_alloc(struct early_log *log)
   {
           struct kmemleak_object *object;
           unsigned long flags;
           int i;
   
           if (!atomic_read(&kmemleak_enabled) || !log->ptr || IS_ERR(log->ptr))
                   return;
   
           /*
            * RCU locking needed to ensure object is not freed via put_object().
            */
           rcu_read_lock();
           object = create_object((unsigned long)log->ptr, log->size,
                                  log->min_count, GFP_ATOMIC);
           if (!object)
                   goto out;
           spin_lock_irqsave(&object->lock, flags);
           for (i = 0; i < log->trace_len; i++)
                   object->trace[i] = log->trace[i];
           object->trace_len = log->trace_len;
           spin_unlock_irqrestore(&object->lock, flags);
   out:
           rcu_read_unlock();
   }
   
   /*
    * Log an early allocated block and populate the stack trace.
    */
   static void early_alloc_percpu(struct early_log *log)
   {
           unsigned int cpu;
           const void __percpu *ptr = log->ptr;
   
           for_each_possible_cpu(cpu) {
                   log->ptr = per_cpu_ptr(ptr, cpu);
                   early_alloc(log);
           }
   }
   
   /**
    * kmemleak_alloc - register a newly allocated object
    * @ptr:        pointer to beginning of the object
    * @size:       size of the object
    * @min_count:  minimum number of references to this object. If during memory
    *              scanning a number of references less than @min_count is found,
    *              the object is reported as a memory leak. If @min_count is 0,
    *              the object is never reported as a leak. If @min_count is -1,
    *              the object is ignored (not scanned and not reported as a leak)
    * @gfp:        kmalloc() flags used for kmemleak internal memory allocations
    *
    * This function is called from the kernel allocators when a new object
    * (memory block) is allocated (kmem_cache_alloc, kmalloc, vmalloc etc.).
    */
   void __ref kmemleak_alloc(const void *ptr, size_t size, int min_count,
                             gfp_t gfp)
   {
           pr_debug("%s(0x%p, %zu, %d)\n", __func__, ptr, size, min_count);
   
           if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
                   create_object((unsigned long)ptr, size, min_count, gfp);
           else if (atomic_read(&kmemleak_early_log))
                   log_early(KMEMLEAK_ALLOC, ptr, size, min_count);
   }
   EXPORT_SYMBOL_GPL(kmemleak_alloc);
   
   /**
    * kmemleak_alloc_percpu - register a newly allocated __percpu object
    * @ptr:        __percpu pointer to beginning of the object
    * @size:       size of the object
    *
    * This function is called from the kernel percpu allocator when a new object
    * (memory block) is allocated (alloc_percpu). It assumes GFP_KERNEL
    * allocation.
    */
   void __ref kmemleak_alloc_percpu(const void __percpu *ptr, size_t size)
   {
           unsigned int cpu;
   
           pr_debug("%s(0x%p, %zu)\n", __func__, ptr, size);
   
           /*
            * Percpu allocations are only scanned and not reported as leaks
            * (min_count is set to 0).
            */
           if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
                   for_each_possible_cpu(cpu)
                           create_object((unsigned long)per_cpu_ptr(ptr, cpu),
                                         size, 0, GFP_KERNEL);
           else if (atomic_read(&kmemleak_early_log))
                   log_early(KMEMLEAK_ALLOC_PERCPU, ptr, size, 0);
   }
   EXPORT_SYMBOL_GPL(kmemleak_alloc_percpu);
   
   /**
    * kmemleak_free - unregister a previously registered object
    * @ptr:        pointer to beginning of the object
    *
    * This function is called from the kernel allocators when an object (memory
    * block) is freed (kmem_cache_free, kfree, vfree etc.).
    */
   void __ref kmemleak_free(const void *ptr)
   {
           pr_debug("%s(0x%p)\n", __func__, ptr);
   
           if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
                   delete_object_full((unsigned long)ptr);
           else if (atomic_read(&kmemleak_early_log))
                   log_early(KMEMLEAK_FREE, ptr, 0, 0);
   }
   EXPORT_SYMBOL_GPL(kmemleak_free);
   
   /**
    * kmemleak_free_part - partially unregister a previously registered object
    * @ptr:        pointer to the beginning or inside the object. This also
    *              represents the start of the range to be freed
    * @size:       size to be unregistered
    *
    * This function is called when only a part of a memory block is freed
    * (usually from the bootmem allocator).
    */
   void __ref kmemleak_free_part(const void *ptr, size_t size)
   {
           pr_debug("%s(0x%p)\n", __func__, ptr);
   
           if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
                   delete_object_part((unsigned long)ptr, size);
           else if (atomic_read(&kmemleak_early_log))
                   log_early(KMEMLEAK_FREE_PART, ptr, size, 0);
   }
   EXPORT_SYMBOL_GPL(kmemleak_free_part);
   
   /**
    * kmemleak_free_percpu - unregister a previously registered __percpu object
    * @ptr:        __percpu pointer to beginning of the object
    *
    * This function is called from the kernel percpu allocator when an object
    * (memory block) is freed (free_percpu).
    */
   void __ref kmemleak_free_percpu(const void __percpu *ptr)
   {
           unsigned int cpu;
   
           pr_debug("%s(0x%p)\n", __func__, ptr);
   
           if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
                   for_each_possible_cpu(cpu)
                           delete_object_full((unsigned long)per_cpu_ptr(ptr,
                                                                         cpu));
           else if (atomic_read(&kmemleak_early_log))
                   log_early(KMEMLEAK_FREE_PERCPU, ptr, 0, 0);
   }
   EXPORT_SYMBOL_GPL(kmemleak_free_percpu);
   
   /**
    * kmemleak_not_leak - mark an allocated object as false positive
    * @ptr:        pointer to beginning of the object
    *
    * Calling this function on an object will cause the memory block to no longer
    * be reported as leak and always be scanned.
    */
   void __ref kmemleak_not_leak(const void *ptr)
   {
           pr_debug("%s(0x%p)\n", __func__, ptr);
   
          if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
                  make_gray_object((unsigned long)ptr);
          else if (atomic_read(&kmemleak_early_log))
                  log_early(KMEMLEAK_NOT_LEAK, ptr, 0, 0);
  }
  EXPORT_SYMBOL(kmemleak_not_leak);
  
  /**
   * kmemleak_ignore - ignore an allocated object
   * @ptr:        pointer to beginning of the object
   *
   * Calling this function on an object will cause the memory block to be
   * ignored (not scanned and not reported as a leak). This is usually done when
   * it is known that the corresponding block is not a leak and does not contain
   * any references to other allocated memory blocks.
   */
  void __ref kmemleak_ignore(const void *ptr)
  {
          pr_debug("%s(0x%p)\n", __func__, ptr);
  
          if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
                  make_black_object((unsigned long)ptr);
          else if (atomic_read(&kmemleak_early_log))
                  log_early(KMEMLEAK_IGNORE, ptr, 0, 0);
  }
  EXPORT_SYMBOL(kmemleak_ignore);
  
  /**
   * kmemleak_scan_area - limit the range to be scanned in an allocated object
   * @ptr:        pointer to beginning or inside the object. This also
   *              represents the start of the scan area
   * @size:       size of the scan area
   * @gfp:        kmalloc() flags used for kmemleak internal memory allocations
   *
   * This function is used when it is known that only certain parts of an object
   * contain references to other objects. Kmemleak will only scan these areas
   * reducing the number false negatives.
   */
  void __ref kmemleak_scan_area(const void *ptr, size_t size, gfp_t gfp)
  {
          pr_debug("%s(0x%p)\n", __func__, ptr);
  
          if (atomic_read(&kmemleak_enabled) && ptr && size && !IS_ERR(ptr))
                  add_scan_area((unsigned long)ptr, size, gfp);
          else if (atomic_read(&kmemleak_early_log))
                  log_early(KMEMLEAK_SCAN_AREA, ptr, size, 0);
  }
  EXPORT_SYMBOL(kmemleak_scan_area);
  
  /**
   * kmemleak_no_scan - do not scan an allocated object
   * @ptr:        pointer to beginning of the object
   *
   * This function notifies kmemleak not to scan the given memory block. Useful
   * in situations where it is known that the given object does not contain any
   * references to other objects. Kmemleak will not scan such objects reducing
   * the number of false negatives.
   */
  void __ref kmemleak_no_scan(const void *ptr)
  {
          pr_debug("%s(0x%p)\n", __func__, ptr);
  
          if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr))
                  object_no_scan((unsigned long)ptr);
          else if (atomic_read(&kmemleak_early_log))
                  log_early(KMEMLEAK_NO_SCAN, ptr, 0, 0);
  }
  EXPORT_SYMBOL(kmemleak_no_scan);
  
  /*
   * Update an object's checksum and return true if it was modified.
   */
  static bool update_checksum(struct kmemleak_object *object)
  {
          u32 old_csum = object->checksum;
  
          if (!kmemcheck_is_obj_initialized(object->pointer, object->size))
                  return false;
  
          object->checksum = crc32(0, (void *)object->pointer, object->size);
          return object->checksum != old_csum;
  }
  
  /*
   * Memory scanning is a long process and it needs to be interruptable. This
   * function checks whether such interrupt condition occurred.
   */
  static int scan_should_stop(void)
  {
          if (!atomic_read(&kmemleak_enabled))
                  return 1;
  
          /*
           * This function may be called from either process or kthread context,
           * hence the need to check for both stop conditions.
           */
          if (current->mm)
                  return signal_pending(current);
          else
                  return kthread_should_stop();
  
          return 0;
  }
  
  /*
   * Scan a memory block (exclusive range) for valid pointers and add those
   * found to the gray list.
   */
  static void scan_block(void *_start, void *_end,
                         struct kmemleak_object *scanned, int allow_resched)
  {
          unsigned long *ptr;
          unsigned long *start = PTR_ALIGN(_start, BYTES_PER_POINTER);
          unsigned long *end = _end - (BYTES_PER_POINTER - 1);
  
          for (ptr = start; ptr < end; ptr++) {
                  struct kmemleak_object *object;
                  unsigned long flags;
                  unsigned long pointer;
  
                  if (allow_resched)
                          cond_resched();
                  if (scan_should_stop())
                          break;
  
                  /* don't scan uninitialized memory */
                  if (!kmemcheck_is_obj_initialized((unsigned long)ptr,
                                                    BYTES_PER_POINTER))
                          continue;
  
                  pointer = *ptr;
  
                  object = find_and_get_object(pointer, 1);
                  if (!object)
                          continue;
                  if (object == scanned) {
                          /* self referenced, ignore */
                          put_object(object);
                          continue;
                  }
  
                  /*
                   * Avoid the lockdep recursive warning on object->lock being
                   * previously acquired in scan_object(). These locks are
                   * enclosed by scan_mutex.
                   */
                  spin_lock_irqsave_nested(&object->lock, flags,
                                           SINGLE_DEPTH_NESTING);
                  if (!color_white(object)) {
                          /* non-orphan, ignored or new */
                          spin_unlock_irqrestore(&object->lock, flags);
                          put_object(object);
                          continue;
                  }
  
                  /*
                   * Increase the object's reference count (number of pointers
                   * to the memory block). If this count reaches the required
                   * minimum, the object's color will become gray and it will be
                   * added to the gray_list.
                   */
                  object->count++;
                  if (color_gray(object)) {
                          list_add_tail(&object->gray_list, &gray_list);
                          spin_unlock_irqrestore(&object->lock, flags);
                          continue;
                  }
  
                  spin_unlock_irqrestore(&object->lock, flags);
                  put_object(object);
          }
  }
  
  /*
   * Scan a memory block corresponding to a kmemleak_object. A condition is
   * that object->use_count >= 1.
   */
  static void scan_object(struct kmemleak_object *object)
  {
          struct kmemleak_scan_area *area;
          struct hlist_node *elem;
          unsigned long flags;
  
          /*
           * Once the object->lock is acquired, the corresponding memory block
           * cannot be freed (the same lock is acquired in delete_object).
           */
          spin_lock_irqsave(&object->lock, flags);
          if (object->flags & OBJECT_NO_SCAN)
                  goto out;
          if (!(object->flags & OBJECT_ALLOCATED))
                  /* already freed object */
                  goto out;
          if (hlist_empty(&object->area_list)) {
                  void *start = (void *)object->pointer;
                  void *end = (void *)(object->pointer + object->size);
  
                  while (start < end && (object->flags & OBJECT_ALLOCATED) &&
                         !(object->flags & OBJECT_NO_SCAN)) {
                          scan_block(start, min(start + MAX_SCAN_SIZE, end),
                                     object, 0);
                          start += MAX_SCAN_SIZE;
  
                          spin_unlock_irqrestore(&object->lock, flags);
                          cond_resched();
                          spin_lock_irqsave(&object->lock, flags);
                  }
          } else
                  hlist_for_each_entry(area, elem, &object->area_list, node)
                          scan_block((void *)area->start,
                                     (void *)(area->start + area->size),
                                     object, 0);
  out:
          spin_unlock_irqrestore(&object->lock, flags);
  }
  
  /*
   * Scan the objects already referenced (gray objects). More objects will be
   * referenced and, if there are no memory leaks, all the objects are scanned.
   */
  static void scan_gray_list(void)
  {
          struct kmemleak_object *object, *tmp;
  
          /*
           * The list traversal is safe for both tail additions and removals
           * from inside the loop. The kmemleak objects cannot be freed from
           * outside the loop because their use_count was incremented.
           */
          object = list_entry(gray_list.next, typeof(*object), gray_list);
          while (&object->gray_list != &gray_list) {
                  cond_resched();
  
                  /* may add new objects to the list */
                  if (!scan_should_stop())
                          scan_object(object);
  
                  tmp = list_entry(object->gray_list.next, typeof(*object),
                                   gray_list);
  
                  /* remove the object from the list and release it */
                  list_del(&object->gray_list);
                  put_object(object);
  
                  object = tmp;
          }
          WARN_ON(!list_empty(&gray_list));
  }
  
  /*
   * Scan data sections and all the referenced memory blocks allocated via the
   * kernel's standard allocators. This function must be called with the
   * scan_mutex held.
   */
  static void kmemleak_scan(void)
  {
          unsigned long flags;
          struct kmemleak_object *object;
          int i;
          int new_leaks = 0;
  
          jiffies_last_scan = jiffies;
  
          /* prepare the kmemleak_object's */
          rcu_read_lock();
          list_for_each_entry_rcu(object, &object_list, object_list) {
                  spin_lock_irqsave(&object->lock, flags);
  #ifdef DEBUG
                  /*
                   * With a few exceptions there should be a maximum of
                   * 1 reference to any object at this point.
                   */
                  if (atomic_read(&object->use_count) > 1) {
                          pr_debug("object->use_count = %d\n",
                                   atomic_read(&object->use_count));
                          dump_object_info(object);
                  }
  #endif
                  /* reset the reference count (whiten the object) */
                  object->count = 0;
                  if (color_gray(object) && get_object(object))
                          list_add_tail(&object->gray_list, &gray_list);
  
                  spin_unlock_irqrestore(&object->lock, flags);
          }
          rcu_read_unlock();
  
          /* data/bss scanning */
          scan_block(_sdata, _edata, NULL, 1);
          scan_block(__bss_start, __bss_stop, NULL, 1);
  
  #ifdef CONFIG_SMP
          /* per-cpu sections scanning */
          for_each_possible_cpu(i)
                  scan_block(__per_cpu_start + per_cpu_offset(i),
                             __per_cpu_end + per_cpu_offset(i), NULL, 1);
  #endif
  
          /*
           * Struct page scanning for each node.
           */
          lock_memory_hotplug();
          for_each_online_node(i) {
                  pg_data_t *pgdat = NODE_DATA(i);
                  unsigned long start_pfn = pgdat->node_start_pfn;
                  unsigned long end_pfn = start_pfn + pgdat->node_spanned_pages;
                  unsigned long pfn;
  
                  for (pfn = start_pfn; pfn < end_pfn; pfn++) {
                          struct page *page;
  
                          if (!pfn_valid(pfn))
                                  continue;
                          page = pfn_to_page(pfn);
                          /* only scan if page is in use */
                          if (page_count(page) == 0)
                                  continue;
                          scan_block(page, page + 1, NULL, 1);
                  }
          }
          unlock_memory_hotplug();
  
          /*
           * Scanning the task stacks (may introduce false negatives).
           */
          if (kmemleak_stack_scan) {
                  struct task_struct *p, *g;
  
                  read_lock(&tasklist_lock);
                  do_each_thread(g, p) {
                          scan_block(task_stack_page(p), task_stack_page(p) +
                                     THREAD_SIZE, NULL, 0);
                  } while_each_thread(g, p);
                  read_unlock(&tasklist_lock);
          }
  
          /*
           * Scan the objects already referenced from the sections scanned
           * above.
           */
          scan_gray_list();
  
          /*
           * Check for new or unreferenced objects modified since the previous
           * scan and color them gray until the next scan.
           */
          rcu_read_lock();
          list_for_each_entry_rcu(object, &object_list, object_list) {
                  spin_lock_irqsave(&object->lock, flags);
                  if (color_white(object) && (object->flags & OBJECT_ALLOCATED)
                      && update_checksum(object) && get_object(object)) {
                          /* color it gray temporarily */
                          object->count = object->min_count;
                          list_add_tail(&object->gray_list, &gray_list);
                  }
                  spin_unlock_irqrestore(&object->lock, flags);
          }
          rcu_read_unlock();
  
          /*
           * Re-scan the gray list for modified unreferenced objects.
           */
          scan_gray_list();
  
          /*
           * If scanning was stopped do not report any new unreferenced objects.
           */
          if (scan_should_stop())
                  return;
  
          /*
           * Scanning result reporting.
           */
          rcu_read_lock();
          list_for_each_entry_rcu(object, &object_list, object_list) {
                  spin_lock_irqsave(&object->lock, flags);
                  if (unreferenced_object(object) &&
                      !(object->flags & OBJECT_REPORTED)) {
                          object->flags |= OBJECT_REPORTED;
                          new_leaks++;
                  }
                  spin_unlock_irqrestore(&object->lock, flags);
          }
          rcu_read_unlock();
  
          if (new_leaks)
                  pr_info("%d new suspected memory leaks (see "
                          "/sys/kernel/debug/kmemleak)\n", new_leaks);
  
  }
  
  /*
   * Thread function performing automatic memory scanning. Unreferenced objects
   * at the end of a memory scan are reported but only the first time.
   */
  static int kmemleak_scan_thread(void *arg)
  {
          static int first_run = 1;
  
          pr_info("Automatic memory scanning thread started\n");
          set_user_nice(current, 10);
  
          /*
           * Wait before the first scan to allow the system to fully initialize.
           */
          if (first_run) {
                  first_run = 0;
                  ssleep(SECS_FIRST_SCAN);
          }
  
          while (!kthread_should_stop()) {
                  signed long timeout = jiffies_scan_wait;
  
                  mutex_lock(&scan_mutex);
                  kmemleak_scan();
                  mutex_unlock(&scan_mutex);
  
                  /* wait before the next scan */
                  while (timeout && !kthread_should_stop())
                          timeout = schedule_timeout_interruptible(timeout);
          }
  
          pr_info("Automatic memory scanning thread ended\n");
  
          return 0;
  }
  
  /*
   * Start the automatic memory scanning thread. This function must be called
   * with the scan_mutex held.
   */
  static void start_scan_thread(void)
  {
          if (scan_thread)
                  return;
          scan_thread = kthread_run(kmemleak_scan_thread, NULL, "kmemleak");
          if (IS_ERR(scan_thread)) {
                  pr_warning("Failed to create the scan thread\n");
                  scan_thread = NULL;
          }
  }
  
  /*
   * Stop the automatic memory scanning thread. This function must be called
   * with the scan_mutex held.
   */
  static void stop_scan_thread(void)
  {
          if (scan_thread) {
                  kthread_stop(scan_thread);
                  scan_thread = NULL;
          }
  }
  
  /*
   * Iterate over the object_list and return the first valid object at or after
   * the required position with its use_count incremented. The function triggers
   * a memory scanning when the pos argument points to the first position.
   */
  static void *kmemleak_seq_start(struct seq_file *seq, loff_t *pos)
  {
          struct kmemleak_object *object;
          loff_t n = *pos;
          int err;
  
          err = mutex_lock_interruptible(&scan_mutex);
          if (err < 0)
                  return ERR_PTR(err);
  
          rcu_read_lock();
          list_for_each_entry_rcu(object, &object_list, object_list) {
                  if (n-- > 0)
                          continue;
                  if (get_object(object))
                          goto out;
          }
          object = NULL;
  out:
          return object;
  }
  
  /*
   * Return the next object in the object_list. The function decrements the
   * use_count of the previous object and increases that of the next one.
   */
  static void *kmemleak_seq_next(struct seq_file *seq, void *v, loff_t *pos)
  {
          struct kmemleak_object *prev_obj = v;
          struct kmemleak_object *next_obj = NULL;
          struct kmemleak_object *obj = prev_obj;
  
          ++(*pos);
  
          list_for_each_entry_continue_rcu(obj, &object_list, object_list) {
                  if (get_object(obj)) {
                          next_obj = obj;
                          break;
                  }
          }
  
          put_object(prev_obj);
          return next_obj;
  }
  
  /*
   * Decrement the use_count of the last object required, if any.
   */
  static void kmemleak_seq_stop(struct seq_file *seq, void *v)
  {
          if (!IS_ERR(v)) {
                  /*
                   * kmemleak_seq_start may return ERR_PTR if the scan_mutex
                   * waiting was interrupted, so only release it if !IS_ERR.
                   */
                  rcu_read_unlock();
                  mutex_unlock(&scan_mutex);
                  if (v)
                          put_object(v);
          }
  }
  
  /*
   * Print the information for an unreferenced object to the seq file.
   */
  static int kmemleak_seq_show(struct seq_file *seq, void *v)
  {
          struct kmemleak_object *object = v;
          unsigned long flags;
  
          spin_lock_irqsave(&object->lock, flags);
          if ((object->flags & OBJECT_REPORTED) && unreferenced_object(object))
                  print_unreferenced(seq, object);
          spin_unlock_irqrestore(&object->lock, flags);
          return 0;
  }
  
  static const struct seq_operations kmemleak_seq_ops = {
          .start = kmemleak_seq_start,
          .next  = kmemleak_seq_next,
          .stop  = kmemleak_seq_stop,
          .show  = kmemleak_seq_show,
  };
  
  static int kmemleak_open(struct inode *inode, struct file *file)
  {
          return seq_open(file, &kmemleak_seq_ops);
  }
  
  static int kmemleak_release(struct inode *inode, struct file *file)
  {
          return seq_release(inode, file);
  }
  
  static int dump_str_object_info(const char *str)
  {
          unsigned long flags;
          struct kmemleak_object *object;
          unsigned long addr;
  
          if (kstrtoul(str, 0, &addr))
                  return -EINVAL;
          object = find_and_get_object(addr, 0);
          if (!object) {
                  pr_info("Unknown object at 0x%08lx\n", addr);
                  return -EINVAL;
          }
  
          spin_lock_irqsave(&object->lock, flags);
          dump_object_info(object);
          spin_unlock_irqrestore(&object->lock, flags);
  
          put_object(object);
          return 0;
  }
  
  /*
   * We use grey instead of black to ensure we can do future scans on the same
   * objects. If we did not do future scans these black objects could
   * potentially contain references to newly allocated objects in the future and
   * we'd end up with false positives.
   */
  static void kmemleak_clear(void)
  {
          struct kmemleak_object *object;
          unsigned long flags;
  
          rcu_read_lock();
          list_for_each_entry_rcu(object, &object_list, object_list) {
                  spin_lock_irqsave(&object->lock, flags);
                  if ((object->flags & OBJECT_REPORTED) &&
                      unreferenced_object(object))
                          __paint_it(object, KMEMLEAK_GREY);
                  spin_unlock_irqrestore(&object->lock, flags);
          }
          rcu_read_unlock();
  }
  
  /*
   * File write operation to configure kmemleak at run-time. The following
   * commands can be written to the /sys/kernel/debug/kmemleak file:
   *   off        - disable kmemleak (irreversible)
   *   stack=on   - enable the task stacks scanning
   *   stack=off  - disable the tasks stacks scanning
   *   scan=on    - start the automatic memory scanning thread
   *   scan=off   - stop the automatic memory scanning thread
   *   scan=...   - set the automatic memory scanning period in seconds (0 to
   *                disable it)
   *   scan       - trigger a memory scan
   *   clear      - mark all current reported unreferenced kmemleak objects as
   *                grey to ignore printing them
   *   dump=...   - dump information about the object found at the given address
   */
  static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
                                size_t size, loff_t *ppos)
  {
          char buf[64];
          int buf_size;
          int ret;
  
          if (!atomic_read(&kmemleak_enabled))
                  return -EBUSY;
  
          buf_size = min(size, (sizeof(buf) - 1));
          if (strncpy_from_user(buf, user_buf, buf_size) < 0)
                  return -EFAULT;
          buf[buf_size] = 0;
  
          ret = mutex_lock_interruptible(&scan_mutex);
          if (ret < 0)
                  return ret;
  
          if (strncmp(buf, "off", 3) == 0)
                  kmemleak_disable();
          else if (strncmp(buf, "stack=on", 8) == 0)
                  kmemleak_stack_scan = 1;
          else if (strncmp(buf, "stack=off", 9) == 0)
                  kmemleak_stack_scan = 0;
          else if (strncmp(buf, "scan=on", 7) == 0)
                  start_scan_thread();
          else if (strncmp(buf, "scan=off", 8) == 0)
                  stop_scan_thread();
          else if (strncmp(buf, "scan=", 5) == 0) {
                  unsigned long secs;
  
                  ret = strict_strtoul(buf + 5, 0, &secs);
                  if (ret < 0)
                          goto out;
                  stop_scan_thread();
                  if (secs) {
                          jiffies_scan_wait = msecs_to_jiffies(secs * 1000);
                          start_scan_thread();
                  }
          } else if (strncmp(buf, "scan", 4) == 0)
                  kmemleak_scan();
          else if (strncmp(buf, "clear", 5) == 0)
                  kmemleak_clear();
          else if (strncmp(buf, "dump=", 5) == 0)
                  ret = dump_str_object_info(buf + 5);
          else
                  ret = -EINVAL;
  
  out:
          mutex_unlock(&scan_mutex);
          if (ret < 0)
                  return ret;
  
          /* ignore the rest of the buffer, only one command at a time */
          *ppos += size;
          return size;
  }
  
  static const struct file_operations kmemleak_fops = {
          .owner          = THIS_MODULE,
          .open           = kmemleak_open,
          .read           = seq_read,
          .write          = kmemleak_write,
          .llseek         = seq_lseek,
          .release        = kmemleak_release,
  };
  
  /*
   * Stop the memory scanning thread and free the kmemleak internal objects if
   * no previous scan thread (otherwise, kmemleak may still have some useful
   * information on memory leaks).
   */
  static void kmemleak_do_cleanup(struct work_struct *work)
  {
          struct kmemleak_object *object;
          bool cleanup = scan_thread == NULL;
  
          mutex_lock(&scan_mutex);
          stop_scan_thread();
  
          if (cleanup) {
                  rcu_read_lock();
                  list_for_each_entry_rcu(object, &object_list, object_list)
                          delete_object_full(object->pointer);
                  rcu_read_unlock();
          }
          mutex_unlock(&scan_mutex);
  }
  
  static DECLARE_WORK(cleanup_work, kmemleak_do_cleanup);
  
  /*
   * Disable kmemleak. No memory allocation/freeing will be traced once this
   * function is called. Disabling kmemleak is an irreversible operation.
   */
  static void kmemleak_disable(void)
  {
          /* atomically check whether it was already invoked */
          if (atomic_cmpxchg(&kmemleak_error, 0, 1))
                  return;
  
          /* stop any memory operation tracing */
          atomic_set(&kmemleak_enabled, 0);
  
          /* check whether it is too early for a kernel thread */
          if (atomic_read(&kmemleak_initialized))
                  schedule_work(&cleanup_work);
  
          pr_info("Kernel memory leak detector disabled\n");
  }
  
  /*
   * Allow boot-time kmemleak disabling (enabled by default).
   */
  static int kmemleak_boot_config(char *str)
  {
          if (!str)
                  return -EINVAL;
          if (strcmp(str, "off") == 0)
                  kmemleak_disable();
          else if (strcmp(str, "on") == 0)
                  kmemleak_skip_disable = 1;
          else
                  return -EINVAL;
          return 0;
  }
  early_param("kmemleak", kmemleak_boot_config);
  
  static void __init print_log_trace(struct early_log *log)
  {
          struct stack_trace trace;
  
          trace.nr_entries = log->trace_len;
          trace.entries = log->trace;
  
          pr_notice("Early log backtrace:\n");
          print_stack_trace(&trace, 2);
  }
  
  /*
   * Kmemleak initialization.
   */
  void __init kmemleak_init(void)
  {
          int i;
          unsigned long flags;
  
  #ifdef CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF
          if (!kmemleak_skip_disable) {
                  atomic_set(&kmemleak_early_log, 0);
                  kmemleak_disable();
                  return;
          }
  #endif
  
          jiffies_min_age = msecs_to_jiffies(MSECS_MIN_AGE);
          jiffies_scan_wait = msecs_to_jiffies(SECS_SCAN_WAIT * 1000);
  
          object_cache = KMEM_CACHE(kmemleak_object, SLAB_NOLEAKTRACE);
          scan_area_cache = KMEM_CACHE(kmemleak_scan_area, SLAB_NOLEAKTRACE);
  
          if (crt_early_log >= ARRAY_SIZE(early_log))
                  pr_warning("Early log buffer exceeded (%d), please increase "
                             "DEBUG_KMEMLEAK_EARLY_LOG_SIZE\n", crt_early_log);
  
          /* the kernel is still in UP mode, so disabling the IRQs is enough */
          local_irq_save(flags);
          atomic_set(&kmemleak_early_log, 0);
          if (atomic_read(&kmemleak_error)) {
                  local_irq_restore(flags);
                  return;
          } else
                  atomic_set(&kmemleak_enabled, 1);
          local_irq_restore(flags);
  
          /*
           * This is the point where tracking allocations is safe. Automatic
           * scanning is started during the late initcall. Add the early logged
           * callbacks to the kmemleak infrastructure.
           */
          for (i = 0; i < crt_early_log; i++) {
                  struct early_log *log = &early_log[i];
  
                  switch (log->op_type) {
                  case KMEMLEAK_ALLOC:
                          early_alloc(log);
                          break;
                  case KMEMLEAK_ALLOC_PERCPU:
                          early_alloc_percpu(log);
                          break;
                  case KMEMLEAK_FREE:
                          kmemleak_free(log->ptr);
                          break;
                  case KMEMLEAK_FREE_PART:
                          kmemleak_free_part(log->ptr, log->size);
                          break;
                  case KMEMLEAK_FREE_PERCPU:
                          kmemleak_free_percpu(log->ptr);
                          break;
                  case KMEMLEAK_NOT_LEAK:
                          kmemleak_not_leak(log->ptr);
                          break;
                  case KMEMLEAK_IGNORE:
                          kmemleak_ignore(log->ptr);
                          break;
                  case KMEMLEAK_SCAN_AREA:
                          kmemleak_scan_area(log->ptr, log->size, GFP_KERNEL);
                          break;
                  case KMEMLEAK_NO_SCAN:
                          kmemleak_no_scan(log->ptr);
                          break;
                  default:
                          kmemleak_warn("Unknown early log operation: %d\n",
                                        log->op_type);
                  }
  
                  if (atomic_read(&kmemleak_warning)) {
                          print_log_trace(log);
                          atomic_set(&kmemleak_warning, 0);
                  }
          }
  }
  
  /*
   * Late initialization function.
   */
  static int __init kmemleak_late_init(void)
  {
          struct dentry *dentry;
  
          atomic_set(&kmemleak_initialized, 1);
  
          if (atomic_read(&kmemleak_error)) {
                  /*
                   * Some error occurred and kmemleak was disabled. There is a
                   * small chance that kmemleak_disable() was called immediately
                   * after setting kmemleak_initialized and we may end up with
                   * two clean-up threads but serialized by scan_mutex.
                   */
                  schedule_work(&cleanup_work);
                  return -ENOMEM;
          }
  
          dentry = debugfs_create_file("kmemleak", S_IRUGO, NULL, NULL,
                                       &kmemleak_fops);
          if (!dentry)
                  pr_warning("Failed to create the debugfs kmemleak file\n");
          mutex_lock(&scan_mutex);
          start_scan_thread();
          mutex_unlock(&scan_mutex);
  
          pr_info("Kernel memory leak detector initialized\n");
  
          return 0;
  }
  late_initcall(kmemleak_late_init);

Cache object: 47a16c31f4ed9dbb5844978dbed11222