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authorJohannes Weiner <jweiner@redhat.com>2011-11-02 13:38:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-11-02 16:07:00 -0700
commita61ed3cec51cfd4877855c24890ab8d3e2b143e3 (patch)
tree3ffb850513b202c8eb0ac09ad6d307719bd39856 /mm
parent9b272977e3b99a8699361d214b51f98c8a9e0e7b (diff)
downloadlinux-stericsson-a61ed3cec51cfd4877855c24890ab8d3e2b143e3.tar.gz
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: charge: putback: SetPageCgroupUsed SetPageLRU 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 <jweiner@redhat.com> Cc: Ying Han <yinghan@google.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Cc: Balbir Singh <bsingharora@gmail.com> Cc: Michal Hocko <mhocko@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c21
1 files changed, 20 insertions, 1 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ce7b35d024e9..01e0c725de65 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -993,6 +993,16 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
return;
pc = lookup_page_cgroup(page);
VM_BUG_ON(PageCgroupAcctLRU(pc));
+ /*
+ * putback: charge:
+ * SetPageLRU SetPageCgroupUsed
+ * smp_mb smp_mb
+ * PageCgroupUsed && add to memcg LRU PageLRU && add to memcg LRU
+ *
+ * Ensure that one of the two sides adds the page to the memcg
+ * LRU during a race.
+ */
+ smp_mb();
if (!PageCgroupUsed(pc))
return;
/* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
@@ -1044,7 +1054,16 @@ static void mem_cgroup_lru_add_after_commit(struct page *page)
unsigned long flags;
struct zone *zone = page_zone(page);
struct page_cgroup *pc = lookup_page_cgroup(page);
-
+ /*
+ * putback: charge:
+ * SetPageLRU SetPageCgroupUsed
+ * smp_mb smp_mb
+ * PageCgroupUsed && add to memcg LRU PageLRU && add to memcg LRU
+ *
+ * Ensure that one of the two sides adds the page to the memcg
+ * LRU during a race.
+ */
+ smp_mb();
/* taking care of that the page is added to LRU while we commit it */
if (likely(!PageLRU(page)))
return;