[B][PATCH v2 1/1] block: do not use interruptible wait anywhere

[Khaled Elmously]

Replying and removing the CC addresses that I spammed. Hopefully if someone were to reply to this thread they'd reply to this message to avoid spamming them again.




On 2018-06-14 10:55:10 , 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
>