linux-kernel - Re: [BUG] Regression introduced with "block: split bios to max possible length"

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Message-ID: <20160121225127.GA30993@localhost.localdomain>
Date:	Thu, 21 Jan 2016 22:51:27 +0000
From:	Keith Busch <keith.busch@...el.com>
To:	Jens Axboe <axboe@...com>
Cc:	Stefan Haberland <sth@...ux.vnet.ibm.com>,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-s390@...r.kernel.org,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>
Subject: Re: [BUG] Regression introduced with "block: split bios to max
 possible length"

On Thu, Jan 21, 2016 at 02:34:28PM -0700, Jens Axboe wrote:
> On 01/21/2016 07:57 AM, Stefan Haberland wrote:
> >Hi,
> >
> >unfortunately commit e36f62042880 "block: split bios to maxpossible length"
> >breaks the DASD driver on s390.  We expect the block requests to be
> >multiple
> >of 4k in size. With the patch applied I see the requests split up in
> >multiple
> >of 512 byte and therefore the requests get rejected and lots of I/Os fail.
> 
> Sigh, that's definitely a bug. I'll take a look at it and see if I
> can get a tested fix in for 4.5-rc1. If not, we'll revert it, again.

My apologies for the trouble. I trust it really is broken, but I don't
quite see how. The patch supposedly splits the transfer to the max size
the request queue says it allows. How does the max allowed size end up
an invalid multiple?