[PATCH RFC] scsi: core: Clear cmd->flags for terminal queuing error

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

If a request can't be queued in scsi_queue_rq(), then we error out with
a blk_status_t code. Such a scenario may be the scsi_device has its
transport offline.

For BLK_STS_RESOURCE or BLK_STS_AGAIN, the request will be requeued in the
block layer. For other errors, the block layer ends the request and so
we won't see it again (until recycled).

Normally when a request completes scmd->flags is cleared in
scsi_end_request().

However for the error scenario mentioned above, scsi_end_request() is
not called and so scmd->flags is not cleared. As such, when the request
is recycled we see the old value in scmd->flags.

Fix this issue by clearing scmd->flags in the error scenario mentioned.

Signed-off-by: John Garry <john.garry@linux.dev>
---
Setting as an RFC as I am not 100% sure that this is correct as there are
lots of paths involved. Sashiko pointed out a related issue in
https://lore.kernel.org/linux-scsi/20260729161243.C918D1F00A3A@smtp.kernel.org/,
but blk_mq_cleanup_rq() -> scsi_cleanup_rq() -> cmd->flags = 0 is only
called for by DM code.

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index af27fd3df8d4..295f8b4afaa7 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1967,6 +1967,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 		 */
 		if (req->rq_flags & RQF_DONTPREP)
 			scsi_mq_uninit_cmd(cmd);
+		cmd->flags = 0;
 		scsi_run_queue_async(sdev);
 		break;
 	}
-- 
2.43.0