Replace the spinlock in blk_mq_find_and_get_req() with an SRCU read lock around the tag iterators. This is done by: - Holding the SRCU read lock in blk_mq_queue_tag_busy_iter(), blk_mq_tagset_busy_iter(), and blk_mq_hctx_has_requests(). - Removing the now-redundant tags->lock from blk_mq_find_and_get_req(). This change fixes lockup issue in scsi_host_busy() in case of shost->host_blocked. Also avoids big tags->lock when reading disk sysfs attribute `inflight`. Reviewed-by: Hannes Reinecke Signed-off-by: Ming Lei --- block/blk-mq-tag.c | 12 ++++++++---- block/blk-mq.c | 24 ++++-------------------- 2 files changed, 12 insertions(+), 24 deletions(-) diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 6c2f5881e0de..7ae431077a32 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -256,13 +256,10 @@ static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags, unsigned int bitnr) { struct request *rq; - unsigned long flags; - spin_lock_irqsave(&tags->lock, flags); rq = tags->rqs[bitnr]; if (!rq || rq->tag != bitnr || !req_ref_inc_not_zero(rq)) rq = NULL; - spin_unlock_irqrestore(&tags->lock, flags); return rq; } @@ -440,7 +437,9 @@ void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset, busy_tag_iter_fn *fn, void *priv) { unsigned int flags = tagset->flags; - int i, nr_tags; + int i, nr_tags, srcu_idx; + + srcu_idx = srcu_read_lock(&tagset->tags_srcu); nr_tags = blk_mq_is_shared_tags(flags) ? 1 : tagset->nr_hw_queues; @@ -449,6 +448,7 @@ void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset, __blk_mq_all_tag_iter(tagset->tags[i], fn, priv, BT_TAG_ITER_STARTED); } + srcu_read_unlock(&tagset->tags_srcu, srcu_idx); } EXPORT_SYMBOL(blk_mq_tagset_busy_iter); @@ -499,6 +499,8 @@ EXPORT_SYMBOL(blk_mq_tagset_wait_completed_request); void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_tag_iter_fn *fn, void *priv) { + int srcu_idx; + /* * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and hctx_table * while the queue is frozen. So we can use q_usage_counter to avoid @@ -507,6 +509,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_tag_iter_fn *fn, if (!percpu_ref_tryget(&q->q_usage_counter)) return; + srcu_idx = srcu_read_lock(&q->tag_set->tags_srcu); if (blk_mq_is_shared_tags(q->tag_set->flags)) { struct blk_mq_tags *tags = q->tag_set->shared_tags; struct sbitmap_queue *bresv = &tags->breserved_tags; @@ -536,6 +539,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_tag_iter_fn *fn, bt_for_each(hctx, q, btags, fn, priv, false); } } + srcu_read_unlock(&q->tag_set->tags_srcu, srcu_idx); blk_queue_exit(q); } diff --git a/block/blk-mq.c b/block/blk-mq.c index c9c6e954bfbc..8191ffac998e 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3415,7 +3415,6 @@ static void blk_mq_clear_rq_mapping(struct blk_mq_tags *drv_tags, struct blk_mq_tags *tags) { struct page *page; - unsigned long flags; /* * There is no need to clear mapping if driver tags is not initialized @@ -3439,15 +3438,6 @@ static void blk_mq_clear_rq_mapping(struct blk_mq_tags *drv_tags, } } } - - /* - * Wait until all pending iteration is done. - * - * Request reference is cleared and it is guaranteed to be observed - * after the ->lock is released. - */ - spin_lock_irqsave(&drv_tags->lock, flags); - spin_unlock_irqrestore(&drv_tags->lock, flags); } void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, @@ -3670,8 +3660,12 @@ static bool blk_mq_hctx_has_requests(struct blk_mq_hw_ctx *hctx) struct rq_iter_data data = { .hctx = hctx, }; + int srcu_idx; + srcu_idx = srcu_read_lock(&hctx->queue->tag_set->tags_srcu); blk_mq_all_tag_iter(tags, blk_mq_has_request, &data); + srcu_read_unlock(&hctx->queue->tag_set->tags_srcu, srcu_idx); + return data.has_rq; } @@ -3891,7 +3885,6 @@ static void blk_mq_clear_flush_rq_mapping(struct blk_mq_tags *tags, unsigned int queue_depth, struct request *flush_rq) { int i; - unsigned long flags; /* The hw queue may not be mapped yet */ if (!tags) @@ -3901,15 +3894,6 @@ static void blk_mq_clear_flush_rq_mapping(struct blk_mq_tags *tags, for (i = 0; i < queue_depth; i++) cmpxchg(&tags->rqs[i], flush_rq, NULL); - - /* - * Wait until all pending iteration is done. - * - * Request reference is cleared and it is guaranteed to be observed - * after the ->lock is released. - */ - spin_lock_irqsave(&tags->lock, flags); - spin_unlock_irqrestore(&tags->lock, flags); } static void blk_free_flush_queue_callback(struct rcu_head *head) -- 2.47.0