On 12/6/18 6:04 PM, jianchao.wang wrote:
>
>
> On 12/7/18 6:20 AM, Jens Axboe 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 about this because it will break the merging promotion for request based DM
> from Ming.
> 396eaf21ee17c476e8f66249fb1f4a39003d0ab4
> (blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback)
>
> We could use some other way to fix this.
That really shouldn't matter as this is the cloned insert, merging should
have been done on the original request.
--
Jens Axboe
