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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id i4sm12548097qke.93.2019.09.16.07.01.27 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 16 Sep 2019 07:01:28 -0700 (PDT) Message-ID: <1568642487.5576.152.camel@lca.pw> Subject: Re: [PATCH] mm/slub: fix a deadlock in shuffle_freelist() From: Qian Cai To: Sebastian Andrzej Siewior , peterz@infradead.org, mingo@redhat.com Cc: akpm@linux-foundation.org, tglx@linutronix.de, thgarnie@google.com, tytso@mit.edu, cl@linux.com, penberg@kernel.org, rientjes@google.com, will@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, keescook@chromium.org Date: Mon, 16 Sep 2019 10:01:27 -0400 In-Reply-To: <20190916090336.2mugbds4rrwxh6uz@linutronix.de> References: <1568392064-3052-1-git-send-email-cai@lca.pw> <20190916090336.2mugbds4rrwxh6uz@linutronix.de> 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=0.000062, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 2019-09-16 at 11:03 +0200, Sebastian Andrzej Siewior wrote: > On 2019-09-13 12:27:44 [-0400], Qian Cai wrote: > =E2=80=A6 > > Chain exists of: > > random_write_wait.lock --> &rq->lock --> batched_entropy_u32.lock > >=20 > > Possible unsafe locking scenario: > >=20 > > CPU0 CPU1 > > ---- ---- > > lock(batched_entropy_u32.lock); > > lock(&rq->lock); > > lock(batched_entropy_u32.lock); > > lock(random_write_wait.lock); >=20 > would this deadlock still occur if lockdep knew that > batched_entropy_u32.lock on CPU0 could be acquired at the same time > as CPU1 acquired its batched_entropy_u32.lock? I suppose that might fix it too if it can teach the lockdep the trick, bu= t it would be better if there is a patch if you have something in mind that co= uld be tested to make sure.