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mm/kmemleak.c: wait for scan completion before disabling free

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A crash is observed when kmemleak_scan accesses the object->pointer,
likely due to the following race.

TASK A             TASK B                     TASK C
kmemleak_write
 (with "scan" and
 NOT "scan=on")
kmemleak_scan()
                   create_object
                   kmem_cache_alloc fails
                   kmemleak_disable
                   kmemleak_do_cleanup
                   kmemleak_free_enabled = 0
                                              kfree
                                              kmemleak_free bails out
                                               (kmemleak_free_enabled is 0)
                                              slub frees object->pointer
update_checksum
crash - object->pointer
 freed (DEBUG_PAGEALLOC)

kmemleak_do_cleanup waits for the scan thread to complete, but not for
direct call to kmemleak_scan via kmemleak_write.  So add a wait for
kmemleak_scan completion before disabling kmemleak_free, and while at it
fix the comment on stop_scan_thread.

[vinmenon@codeaurora.org: fix stop_scan_thread comment]
  Link: http://lkml.kernel.org/r/1522219972-22809-1-git-send-email-vinmenon@codeaurora.org
Link: http://lkml.kernel.org/r/1522063429-18992-1-git-send-email-vinmenon@codeaurora.org
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Git-Commit: 5b909d2e92fc6b741b283cb6f34fa6ecd01fba4c
Git-Repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
Change-Id: Id5ae7f105c70739cc83dd3e4cb3a676410f93632
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
This commit is contained in:
Vinayak Menon 2018-03-29 10:14:09 +11:00 committed by Gerrit - the friendly Code Review server
parent f0a4ec7dbc
commit 002720e74a
1 changed files with 7 additions and 5 deletions
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12
mm/kmemleak.c
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@ -1670,8 +1670,7 @@ static void start_scan_thread(void)
} }
/* /*
* Stop the automatic memory scanning thread. This function must be called * Stop the automatic memory scanning thread.
* with the scan_mutex held.
*/ */
static void stop_scan_thread(void) static void stop_scan_thread(void)
{ {
@ -1934,12 +1933,15 @@ static void kmemleak_do_cleanup(struct work_struct *work)
{ {
stop_scan_thread(); stop_scan_thread();
mutex_lock(&scan_mutex);
/* /*
* Once the scan thread has stopped, it is safe to no longer track * Once it is made sure that kmemleak_scan has stopped, it is safe to no
* object freeing. Ordering of the scan thread stopping and the memory * longer track object freeing. Ordering of the scan thread stopping and
* accesses below is guaranteed by the kthread_stop() function. * the memory accesses below is guaranteed by the kthread_stop()
* function.
*/ */
kmemleak_free_enabled = 0; kmemleak_free_enabled = 0;
mutex_unlock(&scan_mutex);
if (!kmemleak_found_leaks) if (!kmemleak_found_leaks)
__kmemleak_do_cleanup(); __kmemleak_do_cleanup();