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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: Shaohua Li <shli@fusionio.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -308,6 +308,17 @@ int ll_front_merge_fn(struct request_queue *q, struct request *req,
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return ll_new_hw_segment(q, req, bio);
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}
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/*
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* blk-mq uses req->special to carry normal driver per-request payload, it
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* does not indicate a prepared command that we cannot merge with.
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*/
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static bool req_no_special_merge(struct request *req)
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{
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struct request_queue *q = req->q;
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return !q->mq_ops && req->special;
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}
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static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
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struct request *next)
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{
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@ -319,7 +330,7 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
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* First check if the either of the requests are re-queued
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* requests. Can't merge them if they are.
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*/
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if (req->special || next->special)
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if (req_no_special_merge(req) || req_no_special_merge(next))
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return 0;
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/*
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@ -416,7 +427,7 @@ static int attempt_merge(struct request_queue *q, struct request *req,
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if (rq_data_dir(req) != rq_data_dir(next)
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|| req->rq_disk != next->rq_disk
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|| next->special)
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|| req_no_special_merge(next))
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return 0;
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if (req->cmd_flags & REQ_WRITE_SAME &&
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@ -515,7 +526,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
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return false;
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/* must be same device and not a special request */
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if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
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if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
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return false;
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/* only merge integrity protected bio into ditto rq */
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