On 12/6/18 3:28 PM, Mike Snitzer wrote:
> On Thu, Dec 06 2018 at 5:20pm -0500,
> Jens Axboe <axboe@xxxxxxxxx> wrote:
>
>> After the direct dispatch corruption fix, we permanently disallow direct
>> dispatch of non read/write requests. This works fine off the normal IO
>> path, as they will be retried like any other failed direct dispatch
>> request. But for the blk_insert_cloned_request() that only DM uses to
>> bypass the bottom level scheduler, we always first attempt direct
>> dispatch. For some types of requests, that's now a permanent failure,
>> and no amount of retrying will make that succeed.
>>
>> Don't use direct dispatch off the cloned insert path, always just use
>> bypass inserts. This still bypasses the bottom level scheduler, which is
>> what DM wants.
>>
>> Fixes: ffe81d45322c ("blk-mq: fix corruption with direct issue")
>> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>>
>> ---
>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index deb56932f8c4..4c44e6fa0d08 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -2637,7 +2637,8 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request *
>> * bypass a potential scheduler on the bottom device for
>> * insert.
>> */
>> - return blk_mq_request_issue_directly(rq);
>> + blk_mq_request_bypass_insert(rq, true);
>> + return BLK_STS_OK;
>> }
>>
>> spin_lock_irqsave(q->queue_lock, flags);
>
> Not sure what this trailing spin_lock_irqsave(q->queue_lock, flags) is
> about.. but this looks good.
It's because it's against current -git, that is gone from the 4.21 branch.
> I'll cleanup dm-rq.c to do away with the
> extra STS_RESOURCE checks for its call to blk_insert_cloned_request()
> once this lands.
That is indeed a nice benefit, all source based failure cases can be
removed from the caller after this.
--
Jens Axboe
