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 3a0a5299
("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 3ef28e83 ("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>