memcg: close race between charge and putback
There is a potential race between a thread charging a page and another
thread putting it back to the LRU list:
PageLRU && add to memcg LRU PageCgroupUsed && add to memcg LRU
The order of setting one flag and checking the other is crucial, otherwise
the charge may observe !PageLRU while the putback observes !PageCgroupUsed
and the page is not linked to the memcg LRU at all.
Global memory pressure may fix this by trying to isolate and putback the
page for reclaim, where that putback would link it to the memcg LRU again.
Without that, the memory cgroup is undeletable due to a charge whose
physical page can not be found and moved out.
Signed-off-by: Johannes Weiner <firstname.lastname@example.org>
Cc: Ying Han <email@example.com>
Acked-by: KAMEZAWA Hiroyuki <firstname.lastname@example.org>
Cc: Daisuke Nishimura <email@example.com>
Cc: Balbir Singh <firstname.lastname@example.org>
Cc: Michal Hocko <email@example.com>
Signed-off-by: Andrew Morton <firstname.lastname@example.org>
Signed-off-by: Linus Torvalds <email@example.com>
1 file changed