From: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Subject: 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 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@xxxxxxxxxxxxxxxxx
Fixes: aeed1d325d42 ("mm/vmscan.c: generalize shrink_slab() calls in shrink_node()")
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Reported-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Reviewed-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Jan Hadrava <had@xxxxxxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.19+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/mm/vmscan.c~mm-vmscan-check-if-mem-cgroup-is-disabled-or-not-before-calling-memcg-slab-shrinker
+++ a/mm/vmscan.c
@@ -699,7 +699,14 @@ static unsigned long shrink_slab(gfp_t g
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))
_
