linux-kernel - Re: blk-mq flush fix

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Date:	Mon, 28 Oct 2013 10:59:32 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
CC:	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 10/28/2013 10:46 AM, Christoph Hellwig wrote:
> 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.

Yes indeed. Actually the more I think about it, the better I like just
using the normal tagging infrastructure and punting to a reserved tag
for the flush. Just needs adding of the check whether it actually needs
it or not.

-- 
Jens Axboe

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