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[213.151.95.130]) by smtp.gmail.com with ESMTPSA id y20sm2334628wmi.23.2020.01.29.05.29.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jan 2020 05:29:51 -0800 (PST) Date: Wed, 29 Jan 2020 14:29:50 +0100 From: Michal Hocko To: Qian Cai Cc: akpm@linux-foundation.org, penguin-kernel@i-love.sakura.ne.jp, hannes@cmpxchg.org, elver@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+f36cfe60b1006a94f9dc@syzkaller.appspotmail.com Subject: Re: [PATCH -next] mm/page_counter: annotate an intentional data race Message-ID: <20200129132950.GL24244@dhcp22.suse.cz> References: <20200129131242.4329-1-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200129131242.4329-1-cai@lca.pw> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Acked-by: Michal Hocko > --- > 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