[PATCH] blk-mq: cleanup terminal request when it could not be queued

[John Garry <john.garry@linux.dev>]

Sashiko points out that the SCSI midlayer error handling misses some
cleanup for when a request could not be queued and won't be requeued [0].
Specifically, clearing the SCSI cmd flags member is missing. Normally that
would be cleared in the non-error path in scsi_end_request() (which also
calls __blk_mq_end_request()).

Callchain blk_mq_cleanup_rq() -> scsi_cleanup_rq() does all the necessary
cleanup, so call that in blk_mq_dispatch_rq_list() for when there was an
error in the dispatch and the rq will be ended.

Note that dm-rq code calls blk_mq_cleanup_rq() for a cloned rq (or SCSI rq)
for when the clone could not be queued and will be retried, but that path
does not use the sched code (and blk_mq_dispatch_rq_list()).

[0] https://lore.kernel.org/linux-scsi/20260729161243.C918D1F00A3A@smtp.kernel.org/

Suggesested-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: John Garry <john.garry@linux.dev>
---
Maybe SCSI should be doing this cleanup directly, as we now create some
confusion on who should do the cleanup - blk-mq or the driver.

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a26a11c73ee3..eb3a481211d0 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2126,6 +2126,7 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 			blk_mq_handle_dev_resource(rq, list);
 			goto out;
 		default:
+			blk_mq_cleanup_rq(rq);
 			blk_mq_end_request(rq, ret);
 		}
 	} while (!list_empty(list));
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index af27fd3df8d4..1ea65b5eb25c 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1960,13 +1960,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 			cmd->result = DID_NO_CONNECT << 16;
 		else
 			cmd->result = DID_ERROR << 16;
-		/*
-		 * Make sure to release all allocated resources when
-		 * we hit an error, as we will never see this command
-		 * again.
-		 */
-		if (req->rq_flags & RQF_DONTPREP)
-			scsi_mq_uninit_cmd(cmd);
+		/* blk-mq will cleanup our resources as the rq will end */
 		scsi_run_queue_async(sdev);
 		break;
 	}
-- 
2.43.0