From: Qian Cai <cai@lca.pw>
To: akpm@linux-foundation.org
Cc: penguin-kernel@i-love.sakura.ne.jp, hannes@cmpxchg.org,
elver@google.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Qian Cai <cai@lca.pw>,
syzbot+f36cfe60b1006a94f9dc@syzkaller.appspotmail.com
Subject: [PATCH -next] mm/page_counter: annotate an intentional data race
Date: Wed, 29 Jan 2020 08:12:42 -0500 [thread overview]
Message-ID: <20200129131242.4329-1-cai@lca.pw> (raw)
The commit 3e32cb2e0a12 ("mm: memcontrol: lockless page counters") could
had memcg->memsw->failcnt been accessed concurrently as reported by
KCSAN,
BUG: KCSAN: data-race in page_counter_try_charge / page_counter_try_charge
write to 0xffff88809bbf2158 of 8 bytes by task 11782 on cpu 0:
page_counter_try_charge+0x100/0x170 mm/page_counter.c:129
try_charge+0x185/0xbf0 mm/memcontrol.c:2405
__memcg_kmem_charge_memcg+0x4a/0xe0 mm/memcontrol.c:2837
__memcg_kmem_charge+0xcf/0x1b0 mm/memcontrol.c:2877
__alloc_pages_nodemask+0x26c/0x310 mm/page_alloc.c:4780
read to 0xffff88809bbf2158 of 8 bytes by task 11814 on cpu 1:
page_counter_try_charge+0xef/0x170 mm/page_counter.c:129
try_charge+0x185/0xbf0 mm/memcontrol.c:2405
__memcg_kmem_charge_memcg+0x4a/0xe0 mm/memcontrol.c:2837
__memcg_kmem_charge+0xcf/0x1b0 mm/memcontrol.c:2877
__alloc_pages_nodemask+0x26c/0x310 mm/page_alloc.c:4780
Since the "failcnt" counter is tolerant of some degree of inaccuracy and
is only used to report stats, a data race will not be harmful, thus mark
it as an intentional data races with the data_race() macro.
Reported-by: syzbot+f36cfe60b1006a94f9dc@syzkaller.appspotmail.com
Signed-off-by: Qian Cai <cai@lca.pw>
---
mm/page_counter.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/page_counter.c b/mm/page_counter.c
index a17841150906..7c82072cda25 100644
--- a/mm/page_counter.c
+++ b/mm/page_counter.c
@@ -126,7 +126,7 @@ bool page_counter_try_charge(struct page_counter *counter,
* This is racy, but we can live with some
* inaccuracy in the failcnt.
*/
- c->failcnt++;
+ data_race(c->failcnt++);
*fail = c;
goto failed;
}
--
2.21.0 (Apple Git-122.2)
next reply other threads:[~2020-01-29 13:13 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 13:12 Qian Cai [this message]
2020-01-29 13:29 ` [PATCH -next] mm/page_counter: annotate an intentional data race Michal Hocko
2020-02-11 12:16 ` Qian Cai
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