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authorChris Down <chris@chrisdown.name>2020-04-01 21:07:24 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-02 09:35:28 -0700
commitf86b810c2610b08afc82218068d1dfeef02dd0a1 (patch)
tree75c734e95fcf41e1cd7f53801b1631c90a5158b4 /mm/page_counter.c
parent15b42562d46debadaebd77ac1a647abae139a231 (diff)
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>
Diffstat (limited to 'mm/page_counter.c')
-rw-r--r--mm/page_counter.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/mm/page_counter.c b/mm/page_counter.c
index 75d53f15f040..509143f232d8 100644
--- a/mm/page_counter.c
+++ b/mm/page_counter.c
@@ -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));