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[78.151.241.235]) by smtp.gmail.com with ESMTPSA id 75-v6sm4509379wmw.37.2018.05.16.10.33.36 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 16 May 2018 10:33:37 -0700 (PDT) Subject: Re: INFO: task hung in blk_queue_enter To: Tetsuo Handa , syzkaller-bugs@googlegroups.com Cc: syzbot , linux-block@vger.kernel.org, Dan Williams , Jens Axboe , linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org, dvyukov@google.com, Bart Van Assche , Christoph Hellwig , Hannes Reinecke , Johannes Thumshirn , Keith Busch , "Martin K. Petersen" , Martin Steigerwald , Ming Lei , Oleksandr Natalenko , Ross Zwisler References: <0000000000009b212b056ae6dbad@google.com> <343bbbf6-64eb-879e-d19e-96aebb037d47@I-love.SAKURA.ne.jp> From: Alan Jenkins Message-ID: <0609ee2b-fbb6-9122-918a-cc2172ee2cfa@gmail.com> Date: Wed, 16 May 2018 18:33:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > jbd2/sda1-8(PID=2271) is stuck waiting for journal commit operation. > I don't know how this thread is involved to this problem. It feels like it should be a necessary link in the chain. This is the filesystem underneath the loop device. If that hangs, we would expect the loop device to hang, but not vice versa. AIUI, you couldn't reproduce this hang on your own machine. Don't you think, your fuzzer has just found a nice exploit for reiserfs? Alan (It's interesting that you found this hang just after we fixed block_queue_enter() to wait in D state instead of S state.[1]  I don't know syszkaller, so I assume from this it only flagged this case up because of the hung task warning. I.e. syzkaller didn't have its own watchdog that would have failed the test anyway. [1] the commit that caused you to CC me. "block: do not use interruptible wait anywhere" https://github.com/torvalds/linux/commit/1dc3039bc87ae7d19a990c3ee71cfd8a9068f428 )