On 4/12/18 12:11 PM, Alan Jenkins wrote:
> 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.
Applied, thanks.
Still want that test in blktests, though!
--
Jens Axboe
