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.
Signed-off-by: Vinayak Menon <vinmenon@xxxxxxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
---
v2: Fix stop_scan_thread comment
mm/kmemleak.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 8b9afc5..9a085d5 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1667,8 +1667,7 @@ 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)
{
@@ -1931,12 +1930,15 @@ static void kmemleak_do_cleanup(struct work_struct *work)
{
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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