linux-kernel - Re: blk-mq flush fix

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Message-ID: <20131028164641.GA1046@infradead.org>
Date:	Mon, 28 Oct 2013 09:46:41 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Alexander Gordeev <agordeev@...hat.com>,
	Tejun Heo <tj@...nel.org>,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	linux-kernel@...r.kernel.org
Subject: Re: blk-mq flush fix

On Mon, Oct 28, 2013 at 10:29:11AM -0600, Jens Axboe wrote:
> It's not that I think the existing patch is THAT bad, it fits in alright
> with the reserved tagging and works regardless of whether a driver uses
> reserved tags or not. And it does have the upside of not requiring
> special checks or logic for this special non-tagged request that using
> the preallocated would might need.

The problem with it is that it will pass a tag number to the low level
driver which it doesn't expect.  In case the tags are used 1:1 as
hardware tags that would lead to nasy bugs.

At vefy least we'd need to mess with ->tag for this special request.

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