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From: Christoph Hellwig <>
To: Ming Lei <>
Cc: Jens Axboe <>,
Subject: Re: [PATCH] blk-mq: insert passthrough request into hctx->dispatch directly
Date: Wed, 19 Feb 2020 08:36:15 -0800
Message-ID: <> (raw)
In-Reply-To: <>

On Sat, Feb 15, 2020 at 11:21:40AM +0800, Ming Lei wrote:
> For some reason, device may be in one situation which can't handle
> FS request, so STS_RESOURCE is always returned and the FS request
> will be added to hctx->dispatch. However passthrough request may
> be required at that time for fixing the problem. If passthrough
> request is added to scheduler queue, there isn't any chance for
> blk-mq to dispatch it given we prioritize requests in hctx->dispatch.
> Then the FS IO request may never be completed, and IO hang is caused.
> So passthrough request has to be added to hctx->dispatch directly.
> Fix this issue by inserting passthrough request into hctx->dispatch
> directly. Then it becomes consistent with original legacy IO request
> path, in which passthrough request is always added to q->queue_head.

Do you have a description of an actual problem this fixes?  Maybe even
a reproducer for blktests?

  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-15  3:21 Ming Lei
2020-02-19 16:36 ` Christoph Hellwig [this message]
2020-02-19 22:10   ` Ming Lei
2020-02-19 23:47     ` dongli.zhang
2020-02-20  1:45       ` Ming Lei
2020-02-20  3:11         ` Dongli Zhang

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