Commit 21e768b4 authored Oct 16, 2017 by Bart Van Assche Committed by Jens Axboe Nov 03, 2017

blk-mq: Make blk_mq_get_request() error path less confusing



blk_mq_get_tag() can modify data->ctx. This means that in the
error path of blk_mq_get_request() data->ctx should be passed to
blk_mq_put_ctx() instead of local_ctx. Note: since blk_mq_put_ctx()
ignores its argument, this patch does not change any functionality.

References: commit 1ad43c00 ("blk-mq: don't leak preempt counter/q_usage_counter when allocating rq failed")
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent c2e82a23

block/blk-mq.c

+7 −5

Original line number	Diff line number	Diff line
		@@ -337,12 +337,14 @@ static struct request blk_mq_get_request(struct request_queue q,
		struct elevator_queue *e = q->elevator;
		struct request *rq;
		unsigned int tag;
		struct blk_mq_ctx *local_ctx = NULL;
		bool put_ctx_on_error = false;

		blk_queue_enter_live(q);
		data->q = q;
		if (likely(!data->ctx))
		data->ctx = local_ctx = blk_mq_get_ctx(q);
		if (likely(!data->ctx)) {
		data->ctx = blk_mq_get_ctx(q);
		put_ctx_on_error = true;
		}
		if (likely(!data->hctx))
		data->hctx = blk_mq_map_queue(q, data->ctx->cpu);
		if (op & REQ_NOWAIT)
		@@ -361,8 +363,8 @@ static struct request blk_mq_get_request(struct request_queue q,

		tag = blk_mq_get_tag(data);
		if (tag == BLK_MQ_TAG_FAIL) {
		if (local_ctx) {
		blk_mq_put_ctx(local_ctx);
		if (put_ctx_on_error) {
		blk_mq_put_ctx(data->ctx);
		data->ctx = NULL;
		}
		blk_queue_exit(q);

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