Messages in this thread | | | Subject | Re: [PATCH v3] blk-mq: fix io hung due to missing commit_rqs | From | Yu Kuai <> | Date | Sat, 13 Aug 2022 14:00:36 +0800 |
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在 2022/07/29 14:35, Yu Kuai 写道: > Hi, Jens > > Can you please consider this patch for v5.20? > friendly ping ... > Thanks, > Kuai > > 在 2022/07/27 11:08, Ming Lei 写道: >> On Tue, Jul 26, 2022 at 08:22:24PM +0800, Yu Kuai wrote: >>> From: Yu Kuai <yukuai3@huawei.com> >>> >>> 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> >> >> Thanks, >> Ming >> >> . >> > > . >
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