On 12/18/2017 11:49 AM, Michal Hocko wrote:
On Sat 16-12-17 22:29:37, Aliaksei Karaliou wrote:
unregister_shrinker() does not have any sanitizing inside so
calling it twice will oops because of double free attempt or so.
This patch makes unregister_shrinker() safer and allows calling
it on resource freeing path without explicit knowledge of whether
shrinker was successfully registered or not.
Tetsuo has made it half way to this already [1]. So maybe we should
fold shrinker->nr_deferred = NULL to his patch and finally merge it.
[1] http://lkml.kernel.org/r/1511523385-6433-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx
Yeah, no problem from my side.
I'm sorry, it seems that I haven't done enough research to realize that
someone is already
looking at that place.
The only my concern/question is whether we should also add some paranoid
stuff in that
extra branch (check that list is empty for example) or not.
Signed-off-by: Aliaksei Karaliou <akaraliou.dev@xxxxxxxxx>
---
mm/vmscan.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 65c4fa26abfa..7cb56db5e9ca 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -281,10 +281,14 @@ EXPORT_SYMBOL(register_shrinker);
*/
void unregister_shrinker(struct shrinker *shrinker)
{
+ if (!shrinker->nr_deferred)
+ return;
+
down_write(&shrinker_rwsem);
list_del(&shrinker->list);
up_write(&shrinker_rwsem);
kfree(shrinker->nr_deferred);
+ shrinker->nr_deferred = NULL;
}
EXPORT_SYMBOL(unregister_shrinker);
--
2.11.0
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