From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com"
<syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com>,
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Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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Subject: Re: INFO: task hung in blk_queue_enter
Date: Wed, 16 May 2018 14:56:42 +0000 [thread overview]
Message-ID: <43327033306c3dd2f7c3717d64ce22415b6f3451.camel@wdc.com> (raw)
In-Reply-To: <b9c33b04-08d7-87a1-3d93-d81a84e6af12@I-love.SAKURA.ne.jp>
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WARNING: multiple messages have this Message-ID (diff)
From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "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>
Cc: "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>,
"dvyukov@google.com" <dvyukov@google.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 14:56:42 +0000 [thread overview]
Message-ID: <43327033306c3dd2f7c3717d64ce22415b6f3451.camel@wdc.com> (raw)
In-Reply-To: <b9c33b04-08d7-87a1-3d93-d81a84e6af12@I-love.SAKURA.ne.jp>
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. 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 14:56 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 [this message]
2018-05-16 14:56 ` Bart Van Assche
2018-05-16 15:16 ` Dmitry Vyukov
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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