Re: [PATCH] block: do not use interruptible wait anywhere

[Alan Jenkins <alan.christopher.jenkins@xxxxxxxxx>]

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@xxxxxxxxxxxxxxx : 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@xxxxxxxxx>
> >
> > 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@xxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Alan Jenkins <alan.christopher.jenkins@xxxxxxxxx>
> > Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> > (cherry-picked from 1dc3039bc87ae7d19a990c3ee71cfd8a9068f428)
> > Signed-off-by: Khalid Elmously <khalid.elmously@xxxxxxxxxxxxx>
> >
> > ---
> >   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