linux-kernel - Re: [RFC PATCH 1/8] rqbased-dm: allow blk_get_request() to be called from interrupt context

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Message-ID: <20061222140139.GA26033@infradead.org>
Date:	Fri, 22 Dec 2006 14:01:39 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	Kiyoshi Ueda <k-ueda@...jp.nec.com>
Cc:	jens.axboe@...cle.com, agk@...hat.com, mchristi@...hat.com,
	linux-kernel@...r.kernel.org, dm-devel@...hat.com,
	j-nomura@...jp.nec.com
Subject: Re: [RFC PATCH 1/8] rqbased-dm: allow blk_get_request() to be called from interrupt context

On Wed, Dec 20, 2006 at 12:50:02PM -0500, Kiyoshi Ueda wrote:
> Because I'd like to use blk_get_request() in q->request_fn()
> which can be called from interrupt context like below:
>   scsi_io_completion -> scsi_end_request -> scsi_next_command
>   -> scsi_run_queue -> blk_run_queue -> q->request_fn

> Or request should not be allocated in q->request_fn() anyway?
> Do you have any other ideas?

The right long-term fix is to make sure request_fn is only ever called
from process context.  This means moving retry handling to a thread instead
of a softirq, but this will need careful performance testing and tweaking.
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