* [PATCH -next] mm/page_counter: annotate an intentional data race
@ 2020-01-29 13:12 Qian Cai
2020-01-29 13:29 ` Michal Hocko
0 siblings, 1 reply; 3+ messages in thread
From: Qian Cai @ 2020-01-29 13:12 UTC (permalink / raw)
To: akpm
Cc: penguin-kernel, hannes, elver, linux-mm, linux-kernel, Qian Cai,
syzbot+f36cfe60b1006a94f9dc
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)
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH -next] mm/page_counter: annotate an intentional data race
2020-01-29 13:12 [PATCH -next] mm/page_counter: annotate an intentional data race Qian Cai
@ 2020-01-29 13:29 ` Michal Hocko
2020-02-11 12:16 ` Qian Cai
0 siblings, 1 reply; 3+ messages in thread
From: Michal Hocko @ 2020-01-29 13:29 UTC (permalink / raw)
To: Qian Cai
Cc: akpm, penguin-kernel, hannes, elver, linux-mm, linux-kernel,
syzbot+f36cfe60b1006a94f9dc
On Wed 29-01-20 08:12:42, Qian Cai wrote:
> 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>
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> 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)
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH -next] mm/page_counter: annotate an intentional data race
2020-01-29 13:29 ` Michal Hocko
@ 2020-02-11 12:16 ` Qian Cai
0 siblings, 0 replies; 3+ messages in thread
From: Qian Cai @ 2020-02-11 12:16 UTC (permalink / raw)
To: Michal Hocko
Cc: akpm, penguin-kernel, hannes, elver, linux-mm, linux-kernel,
syzbot+f36cfe60b1006a94f9dc
> On Jan 29, 2020, at 8:29 AM, Michal Hocko <mhocko@kernel.org> wrote:
>
> Acked-by: Michal Hocko <mhocko@suse.com>
Andrew, you might forget about picking this up too?
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-02-11 12:16 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-01-29 13:12 [PATCH -next] mm/page_counter: annotate an intentional data race Qian Cai
2020-01-29 13:29 ` Michal Hocko
2020-02-11 12:16 ` Qian Cai
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).