[PATCH] block: do not use interruptible wait anywhere

[Alan Jenkins]

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 at 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 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
>>