[PATCH 5.19 142/158] blk-mq: fix io hung due to missing commit_rqs

Greg Kroah-Hartman
2022-08-29T12:11:44Z

From: Yu Kuai <yukuai3@huawei.com>

commit 65fac0d54f374625b43a9d6ad1f2c212bd41f518 upstream.

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'.

Fixes: d666ba98f849 ("blk-mq: add mq_ops->commit_rqs()")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20220726122224.1790882-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
block/blk-mq.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1925,7 +1925,8 @@ out:
/* 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,
@@ -2678,6 +2679,7 @@ void blk_mq_try_issue_list_directly(stru
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,
@@ -2685,7 +2687,6 @@ void blk_mq_try_issue_list_directly(stru
break;
}
blk_mq_end_request(rq, ret);
- errors++;
} else
queued++;
}