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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id 79sm1147768qkf.129.2020.02.26.05.49.31 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 26 Feb 2020 05:49:32 -0800 (PST) Message-ID: <1582724970.7365.121.camel@lca.pw> Subject: Re: [PATCH v2] mm/vmscan: fix data races at kswapd_classzone_idx From: Qian Cai To: Matthew Wilcox Cc: akpm@linux-foundation.org, elver@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Wed, 26 Feb 2020 08:49:30 -0500 In-Reply-To: <20200226040612.GW24185@bombadil.infradead.org> References: <20200226035827.1285-1-cai@lca.pw> <20200226040612.GW24185@bombadil.infradead.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 2020-02-25 at 20:06 -0800, Matthew Wilcox wrote: > On Tue, Feb 25, 2020 at 10:58:27PM -0500, Qian Cai wrote: > > pgdat->kswapd_classzone_idx could be accessed concurrently in > > wakeup_kswapd(). Plain writes and reads without any lock protection > > result in data races. Fix them by adding a pair of READ|WRITE_ONCE() = as > > well as saving a branch (compilers might well optimize the original c= ode > > in an unintentional way anyway). While at it, also take care of > > pgdat->kswapd_order and non-kswapd threads in allow_direct_reclaim(). >=20 > I don't understand why the usages of kswapd_classzone_idx in kswapd() a= nd > kswapd_try_to_sleep() don't need changing too? kswapd_classzone_idx() > looks safe to me, but I'm prone to missing stupid things that compilers > are allowed to do. Right, I did capture the race this time. I'll post a v3. [=C2=A0=C2=A0924.803628][ T6299] BUG: KCSAN: data-race in kswapd / wakeup= _kswapd=C2=A0 [=C2=A0=C2=A0924.809949][ T6299]=C2=A0=C2=A0 [=C2=A0=C2=A0924.812170][ T6299] write to 0xffff90973ffff2dc of 4 bytes b= y task 820 on cpu 6:=C2=A0 [=C2=A0=C2=A0924.819630][ T6299]=C2=A0=C2=A0kswapd+0x27c/0x8d0=C2=A0 [=C2=A0=C2=A0924.823509][ T6299]=C2=A0=C2=A0kthread+0x1e0/0x200=C2=A0 [=C2=A0=C2=A0924.827471][ T6299]=C2=A0=C2=A0ret_from_fork+0x27/0x50=C2=A0 [=C2=A0=C2=A0924.831774][ T6299]=C2=A0=C2=A0 [=C2=A0=C2=A0924.833987][ T6299] read to 0xffff90973ffff2dc of 4 bytes by= task 6299 on cpu 0:=C2=A0 [=C2=A0=C2=A0924.841442][ T6299]=C2=A0=C2=A0wakeup_kswapd+0xf3/0x450=C2=A0 [=C2=A0=C2=A0924.845838][ T6299]=C2=A0=C2=A0wake_all_kswapds+0x59/0xc0=C2= =A0 [=C2=A0=C2=A0924.850409][ T6299]=C2=A0=C2=A0__alloc_pages_slowpath+0xdcc/= 0x1290=C2=A0 [=C2=A0=C2=A0924.855769][ T6299]=C2=A0=C2=A0__alloc_pages_nodemask+0x3bb/= 0x450=C2=A0 [=C2=A0=C2=A0924.861040][ T6299]=C2=A0=C2=A0alloc_pages_vma+0x8a/0x2c0=C2= =A0 [=C2=A0=C2=A0924.865612][ T6299]=C2=A0=C2=A0do_anonymous_page+0x170/0x700= =C2=A0 [=C2=A0=C2=A0924.870443][ T6299]=C2=A0=C2=A0__handle_mm_fault+0xc9f/0xd00= =C2=A0 [=C2=A0=C2=A0924.875276][ T6299]=C2=A0=C2=A0handle_mm_fault+0xfc/0x2f0=C2= =A0 [=C2=A0=C2=A0924.879849][ T6299]=C2=A0=C2=A0do_page_fault+0x263/0x6f9=C2=A0 [=C2=A0=C2=A0924.884334][ T6299]=C2=A0=C2=A0page_fault+0x34/0x40=C2=A0