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@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@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@wdc.com Cc: stable@vger.kernel.org Signed-off-by: Alan Jenkins alan.christopher.jenkins@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk (cherry-picked from 1dc3039bc87ae7d19a990c3ee71cfd8a9068f428) Signed-off-by: Khalid Elmously khalid.elmously@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