Commit e4d750c9 authored by Jens Axboe's avatar Jens Axboe
Browse files

block: free merged request in the caller 



If we end up doing a request-to-request merge when we have completed
a bio-to-request merge, we free the request from deep down in that
path. For blk-mq-sched, the merge path has to hold the appropriate
lock, but we don't need it for freeing the request. And in fact
holding the lock is problematic, since we are now calling the
mq sched put_rq_private() hook with the lock held. Other call paths
do not hold this lock.

Fix this inconsistency by ensuring that the caller frees a merged
request. Then we can do it outside of the lock, making it both more
efficient and fixing the blk-mq-sched problem of invoking parts of
the scheduler with an unknown lock state.

Reported-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
Reviewed-by: default avatarOmar Sandoval <osandov@fb.com>
parent b973cb7e

block/blk-core.c

+9 −3
Original line number Diff line number Diff line
@@ -1596,7 +1596,7 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio) 
{

	struct blk_plug *plug;

	int el_ret, where = ELEVATOR_INSERT_SORT;

	struct request *req;

	struct request *req, *free;

	unsigned int request_count = 0;

	unsigned int wb_acct;
@@ -1637,15 +1637,21 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio) 
	if (el_ret == ELEVATOR_BACK_MERGE) {

		if (bio_attempt_back_merge(q, req, bio)) {

			elv_bio_merged(q, req, bio);

			if (!attempt_back_merge(q, req))

			free = attempt_back_merge(q, req);

			if (!free)

				elv_merged_request(q, req, el_ret);

			else

				__blk_put_request(q, free);

			goto out_unlock;

		}

	} else if (el_ret == ELEVATOR_FRONT_MERGE) {

		if (bio_attempt_front_merge(q, req, bio)) {

			elv_bio_merged(q, req, bio);

			if (!attempt_front_merge(q, req))

			free = attempt_front_merge(q, req);

			if (!free)

				elv_merged_request(q, req, el_ret);

			else

				__blk_put_request(q, free);

			goto out_unlock;

		}

	}

block/blk-merge.c

+12 −3
Original line number Diff line number Diff line
@@ -733,9 +733,11 @@ static struct request *attempt_merge(struct request_queue *q, 
	if (blk_rq_cpu_valid(next))

		req->cpu = next->cpu;



	/* owner-ship of bio passed from next to req */

	/*

	 * ownership of bio passed from next to req, return 'next' for

	 * the caller to free

	 */

	next->bio = NULL;

	__blk_put_request(q, next);

	return next;

}
@@ -763,12 +765,19 @@ int blk_attempt_req_merge(struct request_queue *q, struct request *rq, 
			  struct request *next)

{

	struct elevator_queue *e = q->elevator;

	struct request *free;



	if (!e->uses_mq && e->type->ops.sq.elevator_allow_rq_merge_fn)

		if (!e->type->ops.sq.elevator_allow_rq_merge_fn(q, rq, next))

			return 0;



	return attempt_merge(q, rq, next) != NULL;

	free = attempt_merge(q, rq, next);

	if (free) {

		__blk_put_request(q, free);

		return 1;

	}



	return 0;

}



bool blk_rq_merge_ok(struct request *rq, struct bio *bio)

block/blk-mq-sched.c

+6 −3
Original line number Diff line number Diff line
@@ -234,7 +234,8 @@ void blk_mq_sched_move_to_dispatch(struct blk_mq_hw_ctx *hctx, 
}

EXPORT_SYMBOL_GPL(blk_mq_sched_move_to_dispatch);



bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio)

bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,

			    struct request **merged_request)

{

	struct request *rq;

	int ret;
@@ -244,7 +245,8 @@ bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio) 
		if (!blk_mq_sched_allow_merge(q, rq, bio))

			return false;

		if (bio_attempt_back_merge(q, rq, bio)) {

			if (!attempt_back_merge(q, rq))

			*merged_request = attempt_back_merge(q, rq);

			if (!*merged_request)

				elv_merged_request(q, rq, ret);

			return true;

		}
@@ -252,7 +254,8 @@ bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio) 
		if (!blk_mq_sched_allow_merge(q, rq, bio))

			return false;

		if (bio_attempt_front_merge(q, rq, bio)) {

			if (!attempt_front_merge(q, rq))

			*merged_request = attempt_front_merge(q, rq);

			if (!*merged_request)

				elv_merged_request(q, rq, ret);

			return true;

		}

block/blk-mq-sched.h

+2 −1
Original line number Diff line number Diff line
@@ -15,7 +15,8 @@ struct request *blk_mq_sched_get_request(struct request_queue *q, struct bio *bi 
void blk_mq_sched_put_request(struct request *rq);



void blk_mq_sched_request_inserted(struct request *rq);

bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio);

bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,

				struct request **merged_request);

bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio);

bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq);

void blk_mq_sched_restart_queues(struct blk_mq_hw_ctx *hctx);

block/mq-deadline.c

+6 −2
Original line number Diff line number Diff line
@@ -371,12 +371,16 @@ static bool dd_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio) 
{

	struct request_queue *q = hctx->queue;

	struct deadline_data *dd = q->elevator->elevator_data;

	int ret;

	struct request *free = NULL;

	bool ret;



	spin_lock(&dd->lock);

	ret = blk_mq_sched_try_merge(q, bio);

	ret = blk_mq_sched_try_merge(q, bio, &free);

	spin_unlock(&dd->lock);



	if (free)

		blk_mq_free_request(free);



	return ret;

}

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