From: Chris Down <chris@xxxxxxxxxxxxxx> Subject: mm, memcg: prevent memory.low load/store tearing This can be set concurrently with reads, which may cause the wrong value to be propagated. Link: http://lkml.kernel.org/r/448206f44b0fa7be9dad2ca2601d2bcb2c0b7844.1584034301.git.chris@xxxxxxxxxxxxxx Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Roman Gushchin <guro@xxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_counter.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- a/mm/page_counter.c~mm-memcg-prevent-memorylow-load-store-tearing +++ a/mm/page_counter.c @@ -17,6 +17,7 @@ static void propagate_protected_usage(st 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(st 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_co { 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)); _
