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mm, memcg: prevent memory.low load/store tearing 

This can be set concurrently with reads, which may cause the wrong value
to be propagated.

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/448206f44b0fa7be9dad2ca2601d2bcb2c0b7844.1584034301.git.chris@chrisdown.name
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Chris Down 2020-04-01 21:07:24 -07:00 committed by Linus Torvalds
parent 15b42562d4
commit f86b810c26
1 changed files with 5 additions and 3 deletions
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8
mm/page_counter.c
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@ -17,6 +17,7 @@ static void propagate_protected_usage(struct page_counter *c,
unsigned long usage)
{
unsigned long protected, old_protected;
unsigned long low;
long delta;
if (!c->parent)
@ -30,8 +31,9 @@ static void propagate_protected_usage(struct page_counter *c,
atomic_long_add(delta, &c->parent->children_min_usage);
}
if (c->low || atomic_long_read(&c->low_usage)) {
protected = min(usage, c->low);
low = READ_ONCE(c->low);
if (low || atomic_long_read(&c->low_usage)) {
protected = min(usage, low);
old_protected = atomic_long_xchg(&c->low_usage, protected);
delta = protected - old_protected;
if (delta)
@ -222,7 +224,7 @@ void page_counter_set_low(struct page_counter *counter, unsigned long nr_pages)
{
struct page_counter *c;
counter->low = nr_pages;
WRITE_ONCE(counter->low, nr_pages);
for (c = counter; c; c = c->parent)
propagate_protected_usage(c, atomic_long_read(&c->usage));