From: Michal Hocko <mhocko@kernel.org>
To: Qian Cai <cai@lca.pw>
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, elver@google.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next] mm/page_counter: mark intentional data races
Date: Wed, 29 Jan 2020 09:51:24 +0100 [thread overview]
Message-ID: <20200129085124.GF24244@dhcp22.suse.cz> (raw)
In-Reply-To: <20200129042019.3632-1-cai@lca.pw>
On Tue 28-01-20 23:20:19, Qian Cai wrote:
> The commit 3e32cb2e0a12 ("mm: memcontrol: lockless page counters")
> had memcg->memsw->failcnt and ->watermark could be accessed concurrently
> as reported by KCSAN,
>
> Reported by Kernel Concurrency Sanitizer on:
> BUG: KCSAN: data-race in page_counter_try_charge / page_counter_try_charge
>
> read to 0xffff8fb18c4cd190 of 8 bytes by task 1081 on cpu 59:
> page_counter_try_charge+0x4d/0x150 mm/page_counter.c:138
> try_charge+0x131/0xd50
> __memcg_kmem_charge_memcg+0x58/0x140
> __memcg_kmem_charge+0xcc/0x280
> __alloc_pages_nodemask+0x1e1/0x450
> alloc_pages_current+0xa6/0x120
> pte_alloc_one+0x17/0xd0
> __pte_alloc+0x3a/0x1f0
> copy_p4d_range+0xc36/0x1990
> copy_page_range+0x21d/0x360
> dup_mmap+0x5f5/0x7a0
> dup_mm+0xa2/0x240
> copy_process+0x1b3f/0x3460
> _do_fork+0xaa/0xa20
> __x64_sys_clone+0x13b/0x170
> do_syscall_64+0x91/0xb47
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> write to 0xffff8fb18c4cd190 of 8 bytes by task 1153 on cpu 120:
> page_counter_try_charge+0x5b/0x150 mm/page_counter.c:139
> try_charge+0x131/0xd50
> mem_cgroup_try_charge+0x159/0x460
> mem_cgroup_try_charge_delay+0x3d/0xa0
> wp_page_copy+0x14d/0x930
> do_wp_page+0x107/0x7b0
> __handle_mm_fault+0xce6/0xd40
> handle_mm_fault+0xfc/0x2f0
> do_page_fault+0x263/0x6f9
> page_fault+0x34/0x40
>
> Since the failcnt and watermark are tolerant of some inaccuracy, a data
> race will not be harmful, thus mark them as intentional data races with
> the data_race() macro.
I am not familiar with KCSAN and git grep for data_race on the current
linux-next doesn't really show any users of this macro. Is there a
general consensus that data_race is going to be used to silence all
KCSAN false positives?
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
> mm/page_counter.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/mm/page_counter.c b/mm/page_counter.c
> index de31470655f6..13934636eafd 100644
> --- a/mm/page_counter.c
> +++ b/mm/page_counter.c
> @@ -82,8 +82,8 @@ void page_counter_charge(struct page_counter *counter, unsigned long nr_pages)
> * This is indeed racy, but we can live with some
> * inaccuracy in the watermark.
> */
> - if (new > c->watermark)
> - c->watermark = new;
> + if (data_race(new > c->watermark))
> + data_race(c->watermark = new);
> }
> }
>
> @@ -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;
> }
> @@ -135,8 +135,8 @@ bool page_counter_try_charge(struct page_counter *counter,
> * Just like with failcnt, we can live with some
> * inaccuracy in the watermark.
> */
> - if (new > c->watermark)
> - c->watermark = new;
> + if (data_race(new > c->watermark))
> + data_race(c->watermark = new);
> }
> return true;
>
> --
> 2.21.0 (Apple Git-122.2)
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-01-29 8:51 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-29 4:20 [PATCH -next] mm/page_counter: mark intentional data races Qian Cai
2020-01-29 8:51 ` Michal Hocko [this message]
2020-01-29 9:06 ` Marco Elver
2020-01-29 9:33 ` Qian Cai
2020-01-29 9:51 ` Qian Cai
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