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block: have plug stored requests hold references to the queue

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Requests that were stored in the cache deliberately didn't hold an enter
reference to the queue, instead we grabbed one every time we pulled a
request out of there. That made for awkward logic on freeing the remainder
of the cached list, if needed, where we had to artificially raise the
queue usage count before each free.

Grab references up front for cached plug requests. That's safer, and also
more efficient.

Fixes: 47c122e35d ("block: pre-allocate requests if plug is started and is a batch")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2021-11-03 05:49:07 -06:00
parent 3b87c6ea67
commit c5fc7b9317
2 changed files with 11 additions and 4 deletions
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8
block/blk-core.c
View File

@ -1643,7 +1643,13 @@ void blk_flush_plug(struct blk_plug *plug, bool from_schedule)
flush_plug_callbacks(plug, from_schedule);
if (!rq_list_empty(plug->mq_list))
blk_mq_flush_plug_list(plug, from_schedule);
if (unlikely(!from_schedule && plug->cached_rq))
/*
* Unconditionally flush out cached requests, even if the unplug
* event came from schedule. Since we know hold references to the
* queue for cached requests, we don't want a blocked task holding
* up a queue freeze/quiesce event.
*/
if (unlikely(!rq_list_empty(plug->cached_rq)))
blk_mq_free_plug_rqs(plug);
}

7
block/blk-mq.c
View File

@ -410,7 +410,10 @@ __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data,
tag_mask &= ~(1UL << i);
rq = blk_mq_rq_ctx_init(data, tags, tag, alloc_time_ns);
rq_list_add(data->cached_rq, rq);
nr++;
}
/* caller already holds a reference, add for remainder */
percpu_ref_get_many(&data->q->q_usage_counter, nr - 1);
data->nr_tags -= nr;
return rq_list_pop(data->cached_rq);
@ -630,10 +633,8 @@ void blk_mq_free_plug_rqs(struct blk_plug *plug)
{
struct request *rq;
while ((rq = rq_list_pop(&plug->cached_rq)) != NULL) {
percpu_ref_get(&rq->q->q_usage_counter);
while ((rq = rq_list_pop(&plug->cached_rq)) != NULL)
blk_mq_free_request(rq);
}
}
static void req_bio_endio(struct request *rq, struct bio *bio,