linux-kernel - Re: 2.6.19-rc3 system freezes when ripping with cdparanoia at ioctl(SG

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Message-ID: <806dafc20611141452y7262df80g6fb7d3c0581f7b7f@mail.gmail.com>
Date:	Tue, 14 Nov 2006 17:52:04 -0500
From:	"Monty Montgomery" <monty@...h.org>
To:	ltuikov@...oo.com
Cc:	"Christoph Hellwig" <hch@...radead.org>, dougg@...que.net,
	"Tejun Heo" <htejun@...il.com>,
	"Brice Goglin" <Brice.Goglin@...-lyon.org>,
	"Jens Axboe" <jens.axboe@...cle.com>,
	"Gregor Jasny" <gjasny@...glemail.com>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>,
	"Jeff Garzik" <jgarzik@...ox.com>, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: 2.6.19-rc3 system freezes when ripping with cdparanoia at ioctl(SG_IO)

On 11/11/06, Luben Tuikov <ltuikov@...oo.com> wrote:
> --- Christoph Hellwig <hch@...radead.org> wrote:
> > On Fri, Nov 10, 2006 at 12:08:15PM -0800, Luben Tuikov wrote:
> > > P.S. I'd love to see SG_DXFER_TO_FROM_DEV completely ripped out
> > > of sg.c, for obvious reasons.  Can you not duplicate the resid "fix"
> > > it provides into "FROM_DEV" -- do apps really rely on it?
> >
> > At the beginning of this thread it was mentioned cdparanio uses it.
> > But in general we can't just rip out userland interfaces, we pretend
> > to have a stable userspace abi (and except for the big sysfs mess that
> > actually comes very close to the truth).
>
> The more reason to think things thorougly when introducing
> new code and architecture into a kernel.

It was introduced for a good reason, and that reason is still relevant
today.  Cdparanoia is not using it gratuitously.  The only problem is
that the implementation had a bug (well, at least two bugs) and only
sg ever implemented it correctly.  Had block and sata implemente dit
correctly, we'd not be having this discussion.

Or you can blame a lower level layer for having no way to inform
mid-level drivers that DMA only completed a partial transfer.

"but anyway"...

This lockup was happening using SATA through the block layer, or does
SATA implement its own version of the ioctl?  Back when I was testing
my probing code, the buggy kernel would reject the request, not lock
up-- did a change make it inot 2.6.18 or later that causes a lockup
instead?

(I never tested with SATA cdroms, as I don't have any.  I tested with
IDE and SCSI and saw correct or detectable behavior)

Monty
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