scsi-mq: fix requests that use a separate CDB buffer

This patch fixes code such as the following with scsi-mq enabled:

    rq = blk_get_request(...);
    blk_rq_set_block_pc(rq);

    rq->cmd = my_cmd_buffer; /* separate CDB buffer */

    blk_execute_rq_nowait(...);

Code like this appears in e.g. sg_start_req() in drivers/scsi/sg.c (for
large CDBs only).  Without this patch, scsi_mq_prep_fn() will set
rq->cmd back to rq->__cmd, causing the wrong CDB to be sent to the device.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 2 insertions, 1 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index c359d72e9d76..bf930f481d43 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1252,7 +1252,6 @@ void blk_rq_set_block_pc(struct request *rq)
         rq->__sector = (sector_t) -1;
         rq->bio = rq->biotail = NULL;
         memset(rq->__cmd, 0, sizeof(rq->__cmd));
-        rq->cmd = rq->__cmd;
 }
 EXPORT_SYMBOL(blk_rq_set_block_pc);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7950f8d7c1bb..4aac82615a46 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -176,6 +176,8 @@ static void blk_mq_rq_ctx_init(struct request_queue *q, struct blk_mq_ctx *ctx,
         /* tag was already set */
         rq->errors = 0;
 
+        rq->cmd = rq->__cmd;
+
         rq->extra_len = 0;
         rq->sense_len = 0;
         rq->resid_len = 0;