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 1ad43c0078b7 ("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>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9eea67c..13cdcce 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -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);