unimore/kernel-hacking-2024-linux-steffo
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blk-mq: call commit_rqs while list empty but error happen

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Blk-mq should call commit_rqs once 'bd.last != true' and no more
request will come(so virtscsi can kick the virtqueue, e.g.). We already
do that in 'blk_mq_dispatch_rq_list/blk_mq_try_issue_list_directly' while
list not empty and 'queued > 0'. However, we can seen the same scene
once the last request in list call queue_rq and return error like
BLK_STS_IOERR which will not requeue the request, and lead that list
empty but need call commit_rqs too(Or the request for virtscsi will stay
timeout until other request kick virtqueue).

We found this problem by do fsstress test with offline/online virtscsi
device repeat quickly.

Fixes: d666ba98f8 ("blk-mq: add mq_ops->commit_rqs()")
Reported-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: yangerkun <yangerkun@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
yangerkun 2020-09-05 19:25:56 +08:00 committed by Jens Axboe
parent 3aab91774b
commit 632bfb6323
1 changed files with 9 additions and 9 deletions
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18
block/blk-mq.c
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@ -1412,6 +1412,11 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
hctx->dispatched[queued_to_index(queued)]++;
/* 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)
q->mq_ops->commit_rqs(hctx);
/*
* Any items that need requeuing? Stuff them into hctx->dispatch,
* that is where we will continue on next queue run.
@ -1425,14 +1430,6 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
blk_mq_release_budgets(q, nr_budgets);
/*
* 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 (q->mq_ops->commit_rqs && queued)
q->mq_ops->commit_rqs(hctx);
spin_lock(&hctx->lock);
list_splice_tail_init(list, &hctx->dispatch);
spin_unlock(&hctx->lock);
@ -2079,6 +2076,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
struct list_head *list)
{
int queued = 0;
int errors = 0;
while (!list_empty(list)) {
blk_status_t ret;
@ -2095,6 +2093,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
break;
}
blk_mq_end_request(rq, ret);
errors++;
} else
queued++;
}
@ -2104,7 +2103,8 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
* the driver there was more coming, but that turned out to
* be a lie.
*/
if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs && queued)
if ((!list_empty(list) || errors) &&
hctx->queue->mq_ops->commit_rqs && queued)
hctx->queue->mq_ops->commit_rqs(hctx);
}