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

[Bart Van Assche]

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.vanass...@sandisk.com>
Reviewed-by: Christoph Hellwig <h...@lst.de>
Cc: Hannes Reinecke <h...@suse.com>
Cc: Omar Sandoval <osan...@fb.com>
Cc: Ming Lei <ming....@redhat.com>
---
 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