Commit f86b810c authored by Chris Down's avatar Chris Down Committed by Linus Torvalds
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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: default avatarChris Down <>
Signed-off-by: default avatarAndrew Morton <>
Acked-by: default avatarMichal Hocko <>
Cc: Johannes Weiner <>
Cc: Roman Gushchin <>
Cc: Tejun Heo <>

Signed-off-by: default avatarLinus Torvalds <>
parent 15b42562
......@@ -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));
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