FAILED: patch "[PATCH] blk-mq: fix io hung due to missing commit_rqs" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 65fac0d54f374625b43a9d6ad1f2c212bd41f518 Mon Sep 17 00:00:00 2001
From: Yu Kuai <[email protected]>
Date: Tue, 26 Jul 2022 20:22:24 +0800
Subject: [PATCH] blk-mq: fix io hung due to missing commit_rqs

Currently, in virtio_scsi, if 'bd->last' is not set to true while dispatching request, such io will stay in driver's queue, and driver will wait for block layer to dispatch more rqs. However, if block layer failed to dispatch more rq, it should trigger commit_rqs to inform driver.

There is a problem in blk_mq_try_issue_list_directly() that commit_rqs won't be called:

// assume that queue_depth is set to 1, list contains two rq blk_mq_try_issue_list_directly
blk_mq_request_issue_directly
// dispatch first rq
// last is false
__blk_mq_try_issue_directly
blk_mq_get_dispatch_budget
// succeed to get first budget __blk_mq_issue_directly

    scsi_queue_rq
     cmd->flags |= SCMD_LAST
      virtscsi_queuecommand
       kick = (sc->flags & SCMD_LAST) != 0
       // kick is false, first rq won't issue to disk

queued++

blk_mq_request_issue_directly
// dispatch second rq
__blk_mq_try_issue_directly
blk_mq_get_dispatch_budget
// failed to get second budget
ret == BLK_STS_RESOURCE
blk_mq_request_bypass_insert
// errors is still 0

if (!list_empty(list) || errors && ...)
// won't pass, commit_rqs won't be called

In this situation, first rq relied on second rq to dispatch, while second rq relied on first rq to complete, thus they will both hung.

Fix the problem by also treat 'BLK_STS_*RESOURCE' as 'errors' since it means that request is not queued successfully.

Same problem exists in blk_mq_dispatch_rq_list(), 'BLK_STS_*RESOURCE' can't be treated as 'errors' here, fix the problem by calling commit_rqs if queue_rq return 'BLK_STS_*RESOURCE'.

index 3c1e6b6d991d..c96c8c4f751b 100644
@@ -1931,7 +1931,8 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 	/* If we didn't flush the entire list, we could have told the driver
 	 * there was more coming, but that turned out to be a lie.
 	 */
-	if ((!list_empty(list) || errors) && q->mq_ops->commit_rqs && queued)
+	if ((!list_empty(list) || errors || needs_resource ||
+	     ret == BLK_STS_DEV_RESOURCE) && q->mq_ops->commit_rqs && queued)
 		q->mq_ops->commit_rqs(hctx);
 	/*
 	 * Any items that need requeuing? Stuff them into hctx->dispatch,

@@ -2660,6 +2661,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 		list_del_init(&rq->queuelist);
 		ret = blk_mq_request_issue_directly(rq, list_empty(list));
 		if (ret != BLK_STS_OK) {
+			errors++;
 			if (ret == BLK_STS_RESOURCE ||
 					ret == BLK_STS_DEV_RESOURCE) {
 				blk_mq_request_bypass_insert(rq, false,

@@ -2667,7 +2669,6 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 				break;
 			}
 			blk_mq_end_request(rq, ret);
-			errors++;
 		} else
 			queued++;
 	}