kmemleak: allow freeing internal objects after kmemleak was disabled

Currently if kmemleak is disabled, the kmemleak objects can never be
freed, no matter if it's disabled by a user or due to fatal errors.

Those objects can be a big waste of memory.

    OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
  1200264 1197433  99%    0.30K  46164       26    369312K kmemleak_object

With this patch, after kmemleak was disabled you can reclaim memory
with:

	# echo clear > /sys/kernel/debug/kmemleak

Also inform users about this with a printk.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/kmemleak.txt b/Documentation/kmemleak.txt
index b6e3973..6c18be9 100644 (file)
--- a/Documentation/kmemleak.txt
+++ b/Documentation/kmemleak.txt
@@ -53,7 +53,8 @@ Memory scanning parameters can be modified at run-time by writing to the
                  (default 600, 0 to stop the automatic scanning)
   scan         - trigger a memory scan
   clear                - clear list of current memory leak suspects, done by
-                 marking all current reported unreferenced objects grey
+                 marking all current reported unreferenced objects grey,
+                 or free all kmemleak objects if kmemleak has been disabled.
   dump=<addr>  - dump information about the object found at <addr>
 
 Kmemleak can also be disabled at boot-time by passing "kmemleak=off" on
@@ -120,6 +121,18 @@ Then as usual to get your report with:
 
   # cat /sys/kernel/debug/kmemleak
 
+Freeing kmemleak internal objects
+---------------------------------
+
+To allow access to previosuly found memory leaks after kmemleak has been
+disabled by the user or due to an fatal error, internal kmemleak objects
+won't be freed when kmemleak is disabled, and those objects may occupy
+a large part of physical memory.
+
+In this situation, you may reclaim memory with:
+
+  # echo clear > /sys/kernel/debug/kmemleak
+
 Kmemleak API
 ------------
 

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 474379e..06cd220 100644 (file)
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1600,6 +1600,8 @@ static void kmemleak_clear(void)
        kmemleak_found_leaks = false;
 }
 
+static void __kmemleak_do_cleanup(void);
+
 /*
  * File write operation to configure kmemleak at run-time. The following
  * commands can be written to the /sys/kernel/debug/kmemleak file:
@@ -1612,7 +1614,8 @@ static void kmemleak_clear(void)
  *               disable it)
  *   scan      - trigger a memory scan
  *   clear     - mark all current reported unreferenced kmemleak objects as
- *               grey to ignore printing them
+ *               grey to ignore printing them, or free all kmemleak objects
+ *               if kmemleak has been disabled.
  *   dump=...  - dump information about the object found at the given address
  */
 static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
@@ -1622,9 +1625,6 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
        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;
@@ -1634,6 +1634,19 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
        if (ret < 0)
                return ret;
 
+       if (strncmp(buf, "clear", 5) == 0) {
+               if (atomic_read(&kmemleak_enabled))
+                       kmemleak_clear();
+               else
+                       __kmemleak_do_cleanup();
+               goto out;
+       }
+
+       if (!atomic_read(&kmemleak_enabled)) {
+               ret = -EBUSY;
+               goto out;
+       }
+
        if (strncmp(buf, "off", 3) == 0)
                kmemleak_disable();
        else if (strncmp(buf, "stack=on", 8) == 0)
@@ -1657,8 +1670,6 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
                }
        } 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
@@ -1683,6 +1694,16 @@ static const struct file_operations kmemleak_fops = {
        .release        = kmemleak_release,
 };
 
+static void __kmemleak_do_cleanup(void)
+{
+       struct kmemleak_object *object;
+
+       rcu_read_lock();
+       list_for_each_entry_rcu(object, &object_list, object_list)
+               delete_object_full(object->pointer);
+       rcu_read_unlock();
+}
+
 /*
  * Stop the memory scanning thread and free the kmemleak internal objects if
  * no previous scan thread (otherwise, kmemleak may still have some useful
@@ -1690,17 +1711,14 @@ static const struct file_operations kmemleak_fops = {
  */
 static void kmemleak_do_cleanup(struct work_struct *work)
 {
-       struct kmemleak_object *object;
-
        mutex_lock(&scan_mutex);
        stop_scan_thread();
 
-       if (!kmemleak_found_leaks) {
-               rcu_read_lock();
-               list_for_each_entry_rcu(object, &object_list, object_list)
-                       delete_object_full(object->pointer);
-               rcu_read_unlock();
-       }
+       if (!kmemleak_found_leaks)
+               __kmemleak_do_cleanup();
+       else
+               pr_info("Kmemleak disabled without freeing internal data. "
+                       "Reclaim the memory with \"echo clear > /sys/kernel/debug/kmemleak\"\n");
        mutex_unlock(&scan_mutex);
 }