From: Tetsuo Handa Subject: Re: INFO: task hung in blk_queue_enter Date: Mon, 4 Jun 2018 22:13:23 +0900 Message-ID: <09a33861-2ddc-1a13-19f6-2a1998ca3ec5@i-love.sakura.ne.jp> References: <43327033306c3dd2f7c3717d64ce22415b6f3451.camel@wdc.com> <6db16aa3a7c56b6dcca2d10b4e100a780c740081.camel@wdc.com> <201805220652.BFH82351.SMQFFOJOtFOVLH@I-love.SAKURA.ne.jp> <201805222020.FEJ82897.OFtJMFHOVLQOSF@I-love.SAKURA.ne.jp> <25708e84-6f35-04c3-a2e4-6854f0ed9e78@I-love.SAKURA.ne.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Bart Van Assche , LKML , linux-block@vger.kernel.org, Johannes Thumshirn , Alan Jenkins , syzbot , "Martin K. Petersen" , Jens Axboe , Dan Williams , Christoph Hellwig , oleksandr@natalenko.name, ming.lei@redhat.com, martin@lichtvoll.de, Hannes Reinecke , syzkaller-bugs , Ross Zwisler , keith.busch@intel.com, linux-ext4@vger.kernel.org To: Dmitry Vyukov Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On 2018/06/04 20:46, Dmitry Vyukov wrote: > On Fri, Jun 1, 2018 at 12:10 PM, Tetsuo Handa > wrote: >> Tetsuo Handa wrote: >>> Since sum of percpu_count did not change after percpu_ref_kill(), this is >>> not a race condition while folding percpu counter values into atomic counter >>> value. That is, for some reason, someone who is responsible for calling >>> percpu_ref_put(&q->q_usage_counter) (presumably via blk_queue_exit()) is >>> unable to call percpu_ref_put(). >>> But I don't know how to find someone who is failing to call percpu_ref_put()... >> >> I found the someone. It was already there in the backtrace... > > Nice! > > Do I understand it correctly that this bug is probably the root cause > of a whole lot of syzbot "task hung" reports? E.g. this one too? > https://syzkaller.appspot.com/bug?id=cdc4add60bb95a4da3fec27c5fe6d75196b7f976 > I guess we will need to sweep close everything related to > filesystems/block devices when this is committed? > I can't tell it. We still have lockdep warning for loop module. Also, I suspect that hung tasks waiting for page bit might be related to binder module. Since we are about to merge "kernel/hung_task.c: show all hung tasks before panic" patch, we might be able to get more hints after 4.18-rc1.