From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "dvyukov@google.com" <dvyukov@google.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"jthumshirn@suse.de" <jthumshirn@suse.de>,
"alan.christopher.jenkins@gmail.com"
<alan.christopher.jenkins@gmail.com>,
"syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com"
<syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com>,
"penguin-kernel@i-love.sakura.ne.jp"
<penguin-kernel@i-love.sakura.ne.jp>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"axboe@kernel.dk" <axboe@kernel.dk>,
"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
"hch@lst.de" <hch@lst.de>,
"oleksandr@natalenko.name" <oleksandr@natalenko.name>,
"ming.lei@redhat.com" <ming.lei@redhat.com>,
"martin@lichtvoll.de" <martin@lichtvoll.de>,
"hare@suse.com" <hare@suse.com>,
"syzkaller-bugs@googlegroups.com"
<syzkaller-bugs@googlegroups.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 15:37:24 +0000 [thread overview]
Message-ID: <6db16aa3a7c56b6dcca2d10b4e100a780c740081.camel@wdc.com> (raw)
In-Reply-To: <CACT4Y+ZJwvROpBmKWF08fTd2AH=dO-a5+dzCzZua_vVFjiCRBw@mail.gmail.com>
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WARNING: multiple messages have this Message-ID
From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "dvyukov@google.com" <dvyukov@google.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"jthumshirn@suse.de" <jthumshirn@suse.de>,
"alan.christopher.jenkins@gmail.com"
<alan.christopher.jenkins@gmail.com>,
"syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com"
<syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com>,
"penguin-kernel@i-love.sakura.ne.jp"
<penguin-kernel@i-love.sakura.ne.jp>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"axboe@kernel.dk" <axboe@kernel.dk>,
"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
"hch@lst.de" <hch@lst.de>,
"oleksandr@natalenko.name" <oleksandr@natalenko.name>,
"ming.lei@redhat.com" <ming.lei@redhat.com>,
"martin@lichtvoll.de" <martin@lichtvoll.de>,
"hare@suse.com" <hare@suse.com>,
"syzkaller-bugs@googlegroups.com"
<syzkaller-bugs@googlegroups.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 15:37:24 +0000 [thread overview]
Message-ID: <6db16aa3a7c56b6dcca2d10b4e100a780c740081.camel@wdc.com> (raw)
In-Reply-To: <CACT4Y+ZJwvROpBmKWF08fTd2AH=dO-a5+dzCzZua_vVFjiCRBw@mail.gmail.com>
On Wed, 2018-05-16 at 17:16 +0200, Dmitry Vyukov wrote:
> 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:
> > > 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?
Because that change conflicts with the purpose of queue freezing and also because
that change would inject I/O errors in code paths that shouldn't inject I/O errors.
Please have a look at e.g. generic_make_request(). From the start of that function:
if (blk_queue_enter(q, flags) < 0) {
if (!blk_queue_dying(q) && (bio->bi_opf & REQ_NOWAIT))
bio_wouldblock_error(bio);
else
bio_io_error(bio);
return ret;
}
The above patch changes the behavior of blk_queue_enter() code from waiting while
q->mq_freeze_depth != 0 into returning -ENODEV while the request queue is frozen.
That will cause generic_make_request() to call bio_io_error(bio) while a request
queue is frozen if REQ_NOWAIT has not been set, which is the default behavior. So
any operation that freezes the queue temporarily, e.g. changing the queue depth,
concurrently with I/O processing can cause I/O to fail with -ENODEV. As you
probably know failure of write requests has very annoying consequences. It e.g.
causes filesystems to go into read-only mode. That's why I think that the above
change is completely wrong.
Bart.
WARNING: multiple messages have this Message-ID
From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "dvyukov@google.com" <dvyukov@google.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"jthumshirn@suse.de" <jthumshirn@suse.de>,
"alan.christopher.jenkins@gmail.com"
<alan.christopher.jenkins@gmail.com>,
"syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com"
<syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com>,
"penguin-kernel@i-love.sakura.ne.jp"
<penguin-kernel@i-love.sakura.ne.jp>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"axboe@kernel.dk" <axboe@kernel.dk>,
"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
"hch@lst.de" <hch@lst.de>,
"oleksandr@natalenko.name" <oleksandr@natalenko.name>,
"ming.lei@redhat.com" <ming.lei@redhat.com>,
"martin@lichtvoll.de" <martin@lichtvoll.de>,
"hare@suse.c
Subject: Re: INFO: task hung in blk_queue_enter
Date: Wed, 16 May 2018 15:37:24 +0000 [thread overview]
Message-ID: <6db16aa3a7c56b6dcca2d10b4e100a780c740081.camel@wdc.com> (raw)
In-Reply-To: <CACT4Y+ZJwvROpBmKWF08fTd2AH=dO-a5+dzCzZua_vVFjiCRBw@mail.gmail.com>
On Wed, 2018-05-16 at 17:16 +0200, Dmitry Vyukov wrote:
> 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:
> > > 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?
Because that change conflicts with the purpose of queue freezing and also because
that change would inject I/O errors in code paths that shouldn't inject I/O errors.
Please have a look at e.g. generic_make_request(). From the start of that function:
if (blk_queue_enter(q, flags) < 0) {
if (!blk_queue_dying(q) && (bio->bi_opf & REQ_NOWAIT))
bio_wouldblock_error(bio);
else
bio_io_error(bio);
return ret;
}
The above patch changes the behavior of blk_queue_enter() code from waiting while
q->mq_freeze_depth != 0 into returning -ENODEV while the request queue is frozen.
That will cause generic_make_request() to call bio_io_error(bio) while a request
queue is frozen if REQ_NOWAIT has not been set, which is the default behavior. So
any operation that freezes the queue temporarily, e.g. changing the queue depth,
concurrently with I/O processing can cause I/O to fail with -ENODEV. As you
probably know failure of write requests has very annoying consequences. It e.g.
causes filesystems to go into read-only mode. That's why I think that the above
change is completely wrong.
Bart.
next prev parent reply other threads:[~2018-05-16 15:37 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-28 11:24 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
2018-05-16 15:16 ` Dmitry Vyukov
2018-05-16 15:37 ` Bart Van Assche [this message]
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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