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block: free merged request in the caller

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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: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
This commit is contained in:
Jens Axboe 2017-02-03 09:48:28 -07:00
parent b973cb7e89
commit e4d750c977
5 changed files with 35 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
block/blk-core.c
View File

@ -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;
}
}

15
block/blk-merge.c
View File

@ -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)

9
block/blk-mq-sched.c
View File

@ -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;
}

3
block/blk-mq-sched.h
View File

@ -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);

8
block/mq-deadline.c
View File

@ -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;
}