[PATCH v3 06/12] blk-mq: Initialize a request before assigning a tag

[Bart Van Assche <bart.vanassche@xxxxxxxxxxx>]

Initialization of blk-mq requests is a bit weird: blk_mq_rq_ctx_init()
is called after a value has been assigned to .rq_flags and .rq_flags
is initialized in __blk_mq_finish_request(). Call blk_mq_rq_ctx_init()
before modifying any struct request members. Initialize .rq_flags in
blk_mq_rq_ctx_init() instead of relying on __blk_mq_finish_request().
Moving the initialization of .rq_flags is fine because all changes
and tests of .rq_flags occur between blk_get_request() and finishing
a request.

Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Omar Sandoval <osandov@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
---
 block/blk-mq.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8cd5261ca1ab..5d9cca62c2f0 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -212,6 +212,7 @@ void blk_mq_rq_ctx_init(struct request_queue *q, struct blk_mq_ctx *ctx,
 	rq->q = q;
 	rq->mq_ctx = ctx;
 	rq->cmd_flags = op;
+	rq->rq_flags = 0;
 	if (blk_queue_io_stat(q))
 		rq->rq_flags |= RQF_IO_STAT;
 	/* do not touch atomic flags, it needs atomic ops against the timer */
@@ -231,7 +232,7 @@ void blk_mq_rq_ctx_init(struct request_queue *q, struct blk_mq_ctx *ctx,
 	rq->nr_integrity_segments = 0;
 #endif
 	rq->special = NULL;
-	/* tag was already set */
+	/* tag will be set by caller */
 	rq->extra_len = 0;
 
 	INIT_LIST_HEAD(&rq->timeout_list);
@@ -257,12 +258,14 @@ struct request *__blk_mq_alloc_request(struct blk_mq_alloc_data *data,
 
 		rq = tags->static_rqs[tag];
 
+		blk_mq_rq_ctx_init(data->q, data->ctx, rq, op);
+
 		if (data->flags & BLK_MQ_REQ_INTERNAL) {
 			rq->tag = -1;
 			rq->internal_tag = tag;
 		} else {
 			if (blk_mq_tag_busy(data->hctx)) {
-				rq->rq_flags = RQF_MQ_INFLIGHT;
+				rq->rq_flags |= RQF_MQ_INFLIGHT;
 				atomic_inc(&data->hctx->nr_active);
 			}
 			rq->tag = tag;
@@ -270,7 +273,6 @@ struct request *__blk_mq_alloc_request(struct blk_mq_alloc_data *data,
 			data->hctx->tags->rqs[rq->tag] = rq;
 		}
 
-		blk_mq_rq_ctx_init(data->q, data->ctx, rq, op);
 		return rq;
 	}
 
@@ -361,7 +363,6 @@ void __blk_mq_finish_request(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
 		atomic_dec(&hctx->nr_active);
 
 	wbt_done(q->rq_wb, &rq->issue_stat);
-	rq->rq_flags = 0;
 
 	clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
 	clear_bit(REQ_ATOM_POLL_SLEPT, &rq->atomic_flags);
-- 
2.12.2