linux-kernel - Re: [PATCH v2] block: do not use interruptible wait anywhere

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Date:   Sat, 14 Apr 2018 13:54:12 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Alan Jenkins <alan.christopher.jenkins@...il.com>,
        linux-block@...r.kernel.org
Cc:     Bart Van Assche <Bart.VanAssche@....com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] block: do not use interruptible wait anywhere

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