From: Vinayak Menon <vinmenon@xxxxxxxxxxxxxx>
Subject: mm/kmemleak.c: wait for scan completion before disabling free
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@xxxxxxxxxxxxxx: fix stop_scan_thread comment]
Link: http://lkml.kernel.org/r/1522219972-22809-1-git-send-email-vinmenon@xxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1522063429-18992-1-git-send-email-vinmenon@xxxxxxxxxxxxxx
Signed-off-by: Vinayak Menon <vinmenon@xxxxxxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kmemleak.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff -puN mm/kmemleak.c~mm-kmemleak-wait-for-scan-completion-before-disabling-free mm/kmemleak.c
--- a/mm/kmemleak.c~mm-kmemleak-wait-for-scan-completion-before-disabling-free
+++ a/mm/kmemleak.c
@@ -1657,8 +1657,7 @@ static void start_scan_thread(void)
}
/*
- * Stop the automatic memory scanning thread. This function must be called
- * with the scan_mutex held.
+ * Stop the automatic memory scanning thread.
*/
static void stop_scan_thread(void)
{
@@ -1921,12 +1920,15 @@ static void kmemleak_do_cleanup(struct w
{
stop_scan_thread();
+ mutex_lock(&scan_mutex);
/*
- * Once the scan thread has stopped, it is safe to no longer track
- * object freeing. Ordering of the scan thread stopping and the memory
- * accesses below is guaranteed by the kthread_stop() function.
+ * Once it is made sure that kmemleak_scan has stopped, it is safe to no
+ * longer track object freeing. Ordering of the scan thread stopping and
+ * the memory accesses below is guaranteed by the kthread_stop()
+ * function.
*/
kmemleak_free_enabled = 0;
+ mutex_unlock(&scan_mutex);
if (!kmemleak_found_leaks)
__kmemleak_do_cleanup();
_
--
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