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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id r25sm2277692otp.22.2019.07.04.14.15.50 (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 04 Jul 2019 14:15:51 -0700 (PDT) Date: Thu, 4 Jul 2019 14:15:33 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: Oleg Nesterov , Qian Cai , axboe@kernel.dk, hch@lst.de, peterz@infradead.org, gkohli@codeaurora.org, mingo@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins Subject: Re: [PATCH] swap_readpage: avoid blk_wake_io_task() if !synchronous In-Reply-To: <20190704123218.87a763f771efad158e1b0a89@linux-foundation.org> Message-ID: References: <1559161526-618-1-git-send-email-cai@lca.pw> <20190704160301.GA5956@redhat.com> <20190704123218.87a763f771efad158e1b0a89@linux-foundation.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 4 Jul 2019, Andrew Morton wrote: > On Thu, 4 Jul 2019 18:03:01 +0200 Oleg Nesterov wrote: > > > swap_readpage() sets waiter = bio->bi_private even if synchronous = F, > > this means that the caller can get the spurious wakeup after return. This > > can be fatal if blk_wake_io_task() does set_current_state(TASK_RUNNING) > > after the caller does set_special_state(), in the worst case the kernel > > can crash in do_task_dead(). > > I think we need a Fixes: and a cc:stable here? > > IIRC, we're fixing 0619317ff8baa2 ("block: add polled wakeup task helper"). Yes, you are right. But catch me by surprise: I had been thinking this was a 5.2 regression. I guess something in 5.2 (doesn't matter what) has made it significantly easier to hit: but now I look at old records, see that I hit it once on 5.0-rc1, then never again until 5.2. Thanks, and to Oleg, Hugh