[PATCH] block: do not use interruptible wait anywhere

[Khalid Elmously]

I screwed up with git-send-email (I think there was a change in its behaviour recently). I shouldn't have sent to -stable - sorry.



On 2018-06-14 16:36:46 , Alan Jenkins wrote:
> Hi Khaled
> 
> As per the Ubuntu bug I quoted in my message to the Ubuntu kernel team, this
> patch has already been accepted in -stable kernel 4.16.7.  AFAIK there is no
> need to resend to -stable, on the basis that they are not currently
> maintaining a 4.15.x kernel.
> 
> I'm not deeply familiar so it is possible I am mis-understanding. (Hence I
> will restrain myself from writing further commentary :-P).
> 
> Regards
> 
> Alan
> 
> 
> On 14/06/18 16:06, Khaled Elmously wrote:
> > stable at vger.kernel.org : Please disregard this whole email thread, and sorry for the spam. Not sure why git-send-email is doing this to me (again).
> > 
> > 
> > 
> > On 2018-06-14 10:53:18 , Khalid Elmously wrote:
> > > From: Alan Jenkins <alan.christopher.jenkins at gmail.com>
> > > 
> > > BugLink: http://bugs.launchpad.net/bugs/1776887
> > > 
> > > When blk_queue_enter() waits for a queue to unfreeze, or unset the
> > > PREEMPT_ONLY flag, do not allow it to be interrupted by a signal.
> > > 
> > > The PREEMPT_ONLY flag was introduced later in commit 3a0a529971ec
> > > ("block, scsi: Make SCSI quiesce and resume work reliably").  Note the SCSI
> > > device is resumed asynchronously, i.e. after un-freezing userspace tasks.
> > > 
> > > So that commit exposed the bug as a regression in v4.15.  A mysterious
> > > SIGBUS (or -EIO) sometimes happened during the time the device was being
> > > resumed.  Most frequently, there was no kernel log message, and we saw Xorg
> > > or Xwayland killed by SIGBUS.[1]
> > > 
> > > [1] E.g. https://bugzilla.redhat.com/show_bug.cgi?id=1553979
> > > 
> > > Without this fix, I get an IO error in this test:
> > > 
> > > # dd if=/dev/sda of=/dev/null iflag=direct & \
> > >    while killall -SIGUSR1 dd; do sleep 0.1; done & \
> > >    echo mem > /sys/power/state ; \
> > >    sleep 5; killall dd  # stop after 5 seconds
> > > 
> > > The interruptible wait was added to blk_queue_enter in
> > > commit 3ef28e83ab15 ("block: generic request_queue reference counting").
> > > Before then, the interruptible wait was only in blk-mq, but I don't think
> > > it could ever have been correct.
> > > 
> > > Reviewed-by: Bart Van Assche <bart.vanassche at wdc.com>
> > > Cc: stable at vger.kernel.org
> > > Signed-off-by: Alan Jenkins <alan.christopher.jenkins at gmail.com>
> > > Signed-off-by: Jens Axboe <axboe at kernel.dk>
> > > (cherry-picked from 1dc3039bc87ae7d19a990c3ee71cfd8a9068f428)
> > > Signed-off-by: Khalid Elmously <khalid.elmously at canonical.com>
> > > 
> > > ---
> > >   block/blk-core.c | 11 ++++-------
> > >   1 file changed, 4 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/block/blk-core.c b/block/blk-core.c
> > > index fc0666354af3..59c91e345eea 100644
> > > --- a/block/blk-core.c
> > > +++ b/block/blk-core.c
> > > @@ -821,7 +821,6 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
> > >   	while (true) {
> > >   		bool success = false;
> > > -		int ret;
> > >   		rcu_read_lock();
> > >   		if (percpu_ref_tryget_live(&q->q_usage_counter)) {
> > > @@ -853,14 +852,12 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
> > >   		 */
> > >   		smp_rmb();
> > > -		ret = wait_event_interruptible(q->mq_freeze_wq,
> > > -				(atomic_read(&q->mq_freeze_depth) == 0 &&
> > > -				 (preempt || !blk_queue_preempt_only(q))) ||
> > > -				blk_queue_dying(q));
> > > +		wait_event(q->mq_freeze_wq,
> > > +			   (atomic_read(&q->mq_freeze_depth) == 0 &&
> > > +			    (preempt || !blk_queue_preempt_only(q))) ||
> > > +			   blk_queue_dying(q));
> > >   		if (blk_queue_dying(q))
> > >   			return -ENODEV;
> > > -		if (ret)
> > > -			return ret;
> > >   	}
> > >   }
> > > -- 
> > > 2.17.1
> > > 
>