Commit e7e24500 authored by Jens Axboe's avatar Jens Axboe
Browse files

blk-mq: don't disallow request merges for req->special being set 



For blk-mq, if a driver has requested per-request payload data
to carry command structures, they are stuffed into req->special.
For an old style request based driver, req->special is used
for the same purpose but indicates that a per-driver request
structure has been prepared for the request already. So for the
old style driver, we do not merge such requests.

As most/all blk-mq drivers will use the payload feature, and
since we have no problem merging on these, make this check
dependent on whether it's a blk-mq enabled driver or not.

Reported-by: default avatarShaohua Li <shli@fusionio.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 92f399c7

block/blk-merge.c

+14 −3
Original line number Diff line number Diff line
@@ -308,6 +308,17 @@ int ll_front_merge_fn(struct request_queue *q, struct request *req, 
	return ll_new_hw_segment(q, req, bio);

}



/*

 * blk-mq uses req->special to carry normal driver per-request payload, it

 * does not indicate a prepared command that we cannot merge with.

 */

static bool req_no_special_merge(struct request *req)

{

	struct request_queue *q = req->q;



	return !q->mq_ops && req->special;

}



static int ll_merge_requests_fn(struct request_queue *q, struct request *req,

				struct request *next)

{
@@ -319,7 +330,7 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req, 
	 * First check if the either of the requests are re-queued

	 * requests.  Can't merge them if they are.

	 */

	if (req->special || next->special)

	if (req_no_special_merge(req) || req_no_special_merge(next))

		return 0;



	/*
@@ -416,7 +427,7 @@ static int attempt_merge(struct request_queue *q, struct request *req, 


	if (rq_data_dir(req) != rq_data_dir(next)

	    || req->rq_disk != next->rq_disk

	    || next->special)

	    || req_no_special_merge(next))

		return 0;



	if (req->cmd_flags & REQ_WRITE_SAME &&
@@ -515,7 +526,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio) 
		return false;



	/* must be same device and not a special request */

	if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)

	if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))

		return false;



	/* only merge integrity protected bio into ditto rq */

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