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>

1 files changed, 14 insertions, 1 deletions

diff --git a/Documentation/kmemleak.txt b/Documentation/kmemleak.txt
index b6e39739a36d..6c18be97f3dd 100644
--- 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
 ------------