From: Dmitry Vyukov <dvyukov@google.com> To: Bart Van Assche <Bart.VanAssche@wdc.com> Cc: "syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com" <syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com>, "syzkaller-bugs@googlegroups.com" <syzkaller-bugs@googlegroups.com>, "dan.j.williams@intel.com" <dan.j.williams@intel.com>, "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>, "penguin-kernel@I-love.SAKURA.ne.jp" <penguin-kernel@i-love.sakura.ne.jp>, "axboe@kernel.dk" <axboe@kernel.dk>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "jthumshirn@suse.de" <jthumshirn@suse.de>, "alan.christopher.jenkins@gmail.com" <alan.christopher.jenkins@gmail.com>, "hch@lst.de" <hch@lst.de>, "martin.petersen@oracle.com" <martin.petersen@oracle.com>, "ming.lei@redhat.com" <ming.lei@redhat.com>, "martin@lichtvoll.de" <martin@lichtvoll.de>, "oleksandr@natalenko.name" <oleksandr@natalenko.name>, "hare@suse.com" <hare@suse.com>, "ross.zwisler@linux.intel.com" <ross.zwisler@linux.intel.com>, "keith.busch@intel.com" <keith.busch@intel.com>, "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org> Subject: Re: INFO: task hung in blk_queue_enter Date: Wed, 16 May 2018 17:16:40 +0200 [thread overview] Message-ID: <CACT4Y+ZJwvROpBmKWF08fTd2AH=dO-a5+dzCzZua_vVFjiCRBw@mail.gmail.com> (raw) In-Reply-To: <43327033306c3dd2f7c3717d64ce22415b6f3451.camel@wdc.com> On Wed, May 16, 2018 at 4:56 PM, Bart Van Assche <Bart.VanAssche@wdc.com> wrote: > On Wed, 2018-05-16 at 22:05 +0900, Tetsuo Handa wrote: >> One ore more threads are waiting for q->mq_freeze_depth to become 0. But the >> thread who incremented q->mq_freeze_depth at blk_freeze_queue_start(q) from >> blk_freeze_queue() is waiting at blk_mq_freeze_queue_wait(). Therefore, >> atomic_read(&q->mq_freeze_depth) == 0 condition for wait_event() in >> blk_queue_enter() will never be satisfied. But what does that wait_event() >> want to do? Isn't "start freezing" a sort of blk_queue_dying(q) == true? >> Since percpu_ref_tryget_live(&q->q_usage_counter) failed and the queue is >> about to be frozen, shouldn't we treat atomic_read(&q->mq_freeze_depth) != 0 >> as if blk_queue_dying(q) == true? That is, something like below: >> >> diff --git a/block/blk-core.c b/block/blk-core.c >> index 85909b4..59e2496 100644 >> --- a/block/blk-core.c >> +++ b/block/blk-core.c >> @@ -951,10 +951,10 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags) >> smp_rmb(); >> >> wait_event(q->mq_freeze_wq, >> - (atomic_read(&q->mq_freeze_depth) == 0 && >> - (preempt || !blk_queue_preempt_only(q))) || >> + atomic_read(&q->mq_freeze_depth) || >> + (preempt || !blk_queue_preempt_only(q)) || >> blk_queue_dying(q)); >> - if (blk_queue_dying(q)) >> + if (atomic_read(&q->mq_freeze_depth) || blk_queue_dying(q)) >> return -ENODEV; >> } >> } > > That change looks wrong to me. Hi Bart, Why does it look wrong to you? > Additionally, I think that you are looking in > the wrong direction. Since blk_mq_freeze_queue_wait() and blk_queue_enter() > work fine for all block drivers except the loop driver I think that you should > have a closer look at how the loop driver uses this block layer functionality. > > Thanks, > > Bart. > > >
WARNING: multiple messages have this Message-ID (diff)
From: Dmitry Vyukov <dvyukov@google.com> To: Bart Van Assche <Bart.VanAssche@wdc.com> Cc: "syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com" <syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com>, "syzkaller-bugs@googlegroups.com" <syzkaller-bugs@googlegroups.com>, "dan.j.williams@intel.com" <dan.j.williams@intel.com>, "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>, "penguin-kernel@I-love.SAKURA.ne.jp" <penguin-kernel@i-love.sakura.ne.jp>, "axboe@kernel.dk" <axboe@kernel.dk>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "jthumshirn@suse.de" <jthumshirn@suse.de>, "alan.christopher.jenkins@gmail.com" <alan.christopher.jenkins@gmail.com>, "hch@lst.de" <hch@lst.de>, "martin.petersen@oracle.com" <martin.petersen@oracle.com>, "ming.lei@redhat.com" <ming.lei@redhat.com>, "martin@lichtvoll.de" <martin@lichtvoll.de>, "oleks Subject: Re: INFO: task hung in blk_queue_enter Date: Wed, 16 May 2018 17:16:40 +0200 [thread overview] Message-ID: <CACT4Y+ZJwvROpBmKWF08fTd2AH=dO-a5+dzCzZua_vVFjiCRBw@mail.gmail.com> (raw) In-Reply-To: <43327033306c3dd2f7c3717d64ce22415b6f3451.camel@wdc.com> On Wed, May 16, 2018 at 4:56 PM, Bart Van Assche <Bart.VanAssche@wdc.com> wrote: > On Wed, 2018-05-16 at 22:05 +0900, Tetsuo Handa wrote: >> One ore more threads are waiting for q->mq_freeze_depth to become 0. But the >> thread who incremented q->mq_freeze_depth at blk_freeze_queue_start(q) from >> blk_freeze_queue() is waiting at blk_mq_freeze_queue_wait(). Therefore, >> atomic_read(&q->mq_freeze_depth) == 0 condition for wait_event() in >> blk_queue_enter() will never be satisfied. But what does that wait_event() >> want to do? Isn't "start freezing" a sort of blk_queue_dying(q) == true? >> Since percpu_ref_tryget_live(&q->q_usage_counter) failed and the queue is >> about to be frozen, shouldn't we treat atomic_read(&q->mq_freeze_depth) != 0 >> as if blk_queue_dying(q) == true? That is, something like below: >> >> diff --git a/block/blk-core.c b/block/blk-core.c >> index 85909b4..59e2496 100644 >> --- a/block/blk-core.c >> +++ b/block/blk-core.c >> @@ -951,10 +951,10 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags) >> smp_rmb(); >> >> wait_event(q->mq_freeze_wq, >> - (atomic_read(&q->mq_freeze_depth) == 0 && >> - (preempt || !blk_queue_preempt_only(q))) || >> + atomic_read(&q->mq_freeze_depth) || >> + (preempt || !blk_queue_preempt_only(q)) || >> blk_queue_dying(q)); >> - if (blk_queue_dying(q)) >> + if (atomic_read(&q->mq_freeze_depth) || blk_queue_dying(q)) >> return -ENODEV; >> } >> } > > That change looks wrong to me. Hi Bart, Why does it look wrong to you? > Additionally, I think that you are looking in > the wrong direction. Since blk_mq_freeze_queue_wait() and blk_queue_enter() > work fine for all block drivers except the loop driver I think that you should > have a closer look at how the loop driver uses this block layer functionality. > > Thanks, > > Bart. > > >
next prev parent reply other threads:[~2018-05-16 15:16 UTC|newest] Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-04-28 11:24 INFO: task hung in blk_queue_enter syzbot 2018-05-15 11:45 ` Tetsuo Handa 2018-05-16 13:05 ` Tetsuo Handa 2018-05-16 14:56 ` Bart Van Assche 2018-05-16 14:56 ` Bart Van Assche 2018-05-16 15:16 ` Dmitry Vyukov [this message] 2018-05-16 15:16 ` Dmitry Vyukov 2018-05-16 15:37 ` Bart Van Assche 2018-05-16 15:37 ` Bart Van Assche 2018-05-16 15:37 ` Bart Van Assche 2018-05-21 21:52 ` Tetsuo Handa 2018-05-22 11:20 ` Tetsuo Handa 2018-06-01 10:10 ` Tetsuo Handa 2018-06-01 17:52 ` Jens Axboe 2018-06-01 23:49 ` Ming Lei 2018-06-02 0:49 ` Jens Axboe 2018-06-02 0:56 ` Jens Axboe 2018-06-02 2:36 ` Ming Lei 2018-06-02 4:31 ` Jens Axboe 2018-06-02 4:54 ` Ming Lei 2018-06-02 8:07 ` Martin Steigerwald 2018-06-02 8:07 ` Martin Steigerwald 2018-06-02 13:48 ` Jens Axboe 2018-06-02 13:48 ` Jens Axboe 2018-06-05 0:27 ` Tetsuo Handa 2018-06-05 0:41 ` Ming Lei 2018-06-07 3:29 ` Ming Lei 2018-06-07 3:29 ` Ming Lei 2018-06-07 13:19 ` Tetsuo Handa 2018-06-04 11:46 ` Dmitry Vyukov 2018-06-04 13:13 ` Tetsuo Handa 2018-05-16 17:33 ` Alan Jenkins
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