Commit c6ba9333 authored Aug 27, 2019 by Ming Lei Committed by Jens Axboe Aug 27, 2019

blk-mq: don't hold q->sysfs_lock in blk_mq_map_swqueue



blk_mq_map_swqueue() is called from blk_mq_init_allocated_queue()
and blk_mq_update_nr_hw_queues(). For the former caller, the kobject
isn't exposed to userspace yet. For the latter caller, hctx sysfs entries
and debugfs are un-registered before updating nr_hw_queues.

On the other hand, commit 2f8f1336 ("blk-mq: always free hctx after
request queue is freed") moves freeing hctx into queue's release
handler, so there won't be race with queue release path too.

So don't hold q->sysfs_lock in blk_mq_map_swqueue().

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent c48dac13

block/blk-mq.c

+0 −7

Original line number	Diff line number	Diff line
		@@ -2456,11 +2456,6 @@ static void blk_mq_map_swqueue(struct request_queue *q)
		struct blk_mq_ctx *ctx;
		struct blk_mq_tag_set *set = q->tag_set;

		/*
		* Avoid others reading imcomplete hctx->cpumask through sysfs
		*/
		mutex_lock(&q->sysfs_lock);

		queue_for_each_hw_ctx(q, hctx, i) {
		cpumask_clear(hctx->cpumask);
		hctx->nr_ctx = 0;
		@@ -2521,8 +2516,6 @@ static void blk_mq_map_swqueue(struct request_queue *q)
		HCTX_TYPE_DEFAULT, i);
		}

		mutex_unlock(&q->sysfs_lock);

		queue_for_each_hw_ctx(q, hctx, i) {
		/*
		* If no software queues are mapped to this hardware queue,

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