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

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

Signed-off-by: Chris Down <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Tejun Heo <[email protected]>
Link: http://lkml.kernel.org/r/448206f44b0fa7be9dad2ca2601d2bcb2c0b7844.1584034301.git.chris@chrisdown.name
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Chris Down authored and Linus Torvalds committed 2020-04-02 09:35:28 -07:00
1 parent 15b42562d4
commit f86b810c26
1 file changed
+5 -3
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mm/page_counter.c
+5 -3
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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));