From fa1e512fac717f34e7c12d7a384c46e90a647392 Mon Sep 17 00:00:00 2001 From: Yang Shi Date: Fri, 2 Aug 2019 21:48:44 -0700 Subject: [PATCH] mm: vmscan: check if mem cgroup is disabled or not before calling memcg slab shrinker Shakeel Butt reported premature oom on kernel with "cgroup_disable=memory" since mem_cgroup_is_root() returns false even though memcg is actually NULL. The drop_caches is also broken. It is because commit aeed1d325d42 ("mm/vmscan.c: generalize shrink_slab() calls in shrink_node()") removed the !memcg check before !mem_cgroup_is_root(). And, surprisingly root memcg is allocated even though memory cgroup is disabled by kernel boot parameter. Add mem_cgroup_disabled() check to make reclaimer work as expected. Link: http://lkml.kernel.org/r/1563385526-20805-1-git-send-email-yang.shi@linux.alibaba.com Fixes: aeed1d325d42 ("mm/vmscan.c: generalize shrink_slab() calls in shrink_node()") Signed-off-by: Yang Shi Reported-by: Shakeel Butt Reviewed-by: Shakeel Butt Reviewed-by: Kirill Tkhai Acked-by: Michal Hocko Cc: Jan Hadrava Cc: Vladimir Davydov Cc: Johannes Weiner Cc: Roman Gushchin Cc: Hugh Dickins Cc: Qian Cai Cc: Kirill A. Shutemov Cc: [4.19+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 44df66a98f2a..dbdc46a84f63 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -699,7 +699,14 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, unsigned long ret, freed = 0; struct shrinker *shrinker; - if (!mem_cgroup_is_root(memcg)) + /* + * The root memcg might be allocated even though memcg is disabled + * via "cgroup_disable=memory" boot parameter. This could make + * mem_cgroup_is_root() return false, then just run memcg slab + * shrink, but skip global shrink. This may result in premature + * oom. + */ + if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) return shrink_slab_memcg(gfp_mask, nid, memcg, priority); if (!down_read_trylock(&shrinker_rwsem))