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mm, memcg: prevent mem_cgroup_protected store tearing 

The read side of this is all protected, but we can still tear if multiple
iterations of mem_cgroup_protected are going at the same time.

There's some intentional racing in mem_cgroup_protected which is ok, but
load/store tearing should be avoided.

Signed-off-by: Chris Down <chris@chrisdown.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/d1e9fbc0379fe8db475d82c8b6fbe048876e12ae.1584034301.git.chris@chrisdown.name
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Chris Down 2020-04-01 21:07:33 -07:00 committed by Linus Torvalds
parent 32d087cdd9
commit b3a7822e5e
1 changed files with 4 additions and 4 deletions
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8
mm/memcontrol.c
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@ -6396,14 +6396,14 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
parent_usage = page_counter_read(&parent->memory);
memcg->memory.emin = effective_protection(usage, parent_usage,
WRITE_ONCE(memcg->memory.emin, effective_protection(usage, parent_usage,
READ_ONCE(memcg->memory.min),
READ_ONCE(parent->memory.emin),
atomic_long_read(&parent->memory.children_min_usage));
atomic_long_read(&parent->memory.children_min_usage)));
memcg->memory.elow = effective_protection(usage, parent_usage,
WRITE_ONCE(memcg->memory.elow, effective_protection(usage, parent_usage,
memcg->memory.low, READ_ONCE(parent->memory.elow),
atomic_long_read(&parent->memory.children_low_usage));
atomic_long_read(&parent->memory.children_low_usage)));
out:
if (usage <= memcg->memory.emin)