From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 076/155] mm, memcg: prevent memory.low load/store tearing Date: Wed, 01 Apr 2020 21:07:24 -0700 Message-ID: <20200402040724.6Xz5_-c5d%akpm@linux-foundation.org> References: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:58428 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726963AbgDBEHZ (ORCPT ); Thu, 2 Apr 2020 00:07:25 -0400 In-Reply-To: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, chris@chrisdown.name, guro@fb.com, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@suse.com, mm-commits@vger.kernel.org, tj@kernel.org, torvalds@linux-foundation.org From: Chris Down 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@chrisdown.name Signed-off-by: Chris Down Acked-by: Michal Hocko Cc: Johannes Weiner Cc: Roman Gushchin Cc: Tejun Heo Signed-off-by: Andrew Morton --- 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)); _