NAK: [PATCH 3/3 Xenial SRU] blk-mq: End unstarted requests on dying queue

[Tim Gardner]

On 05/26/2016 06:58 AM, Christopher Arges wrote:
> On Wed, May 25, 2016 at 08:47:33AM -0600, Tim Gardner wrote:
>> From: Keith Busch <keith.busch at intel.com>
>>
>> BugLink: http://bugs.launchpad.net/bugs/1581034
>>
>> Go directly to ending a request if it wasn't started. Previously, completing a
>> request may invoke a driver callback for a request it didn't initialize.
>>
>> Signed-off-by: Keith Busch <keith.busch at intel.com>
>> Reviewed-by: Sagi Grimberg <sagig at mellanox.com>
>> Reviewed-by: Johannes Thumshirn <jthumshirn at suse.de>
>> Acked-by: Christoph Hellwig <hch at lst.de>
>> Signed-off-by: Jens Axboe <axboe at fb.com>
>> (back ported from commit a59e0f5795fe52dad42a99c00287e3766153b312)
>> Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
>> ---
>>  block/blk-mq.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 93a4e19..3989b2d 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -599,8 +599,10 @@ static void blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
>>  		 * If a request wasn't started before the queue was
>>  		 * marked dying, kill it here or it'll go unnoticed.
>>  		 */
>> -		if (unlikely(blk_queue_dying(rq->q)))
>> -			blk_mq_complete_request(rq, -EIO);
>> +		if (unlikely(blk_queue_dying(rq->q))) {
>> +			rq->errors = -EIO;
>> +			blk_mq_complete_request(rq, rq->errors);
>> +
> 
> Why does this call blk_mq_complete_request instead of blk_mq_end_request per the
> original commit?
> 
This patch ('blk-mq: End unstarted requests on dying queue') came after
commit a59e0f5795fe52dad42a99c00287e3766153b312 ('blk-mq: End unstarted
requests on dying queue') which changes the call from
blk_mq_complete_request(rq, -EIO) to blk_mq_end_request(rq, rq->errors).
If you follow the chain of logic, blk_mq_complete_request() calls
blk_mq_end_request() within the semantics of the driver. Calling
blk_mq_end_request() might have unintended side effects. I chose to
implement the simplest backport possible.

rtg
-- 
Tim Gardner tim.gardner at canonical.com