linux-kernel - Re: [PATCH]: Fix old SCSI adapter crashes with CD-ROM (take 2)

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Message-ID: <20070508165258.GE4163@kernel.dk>
Date:	Tue, 8 May 2007 18:52:58 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Mike Christie <michaelc@...wisc.edu>
Cc:	James Bottomley <James.Bottomley@...elEye.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-scsi@...r.kernel.org, akpm@...l.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH]: Fix old SCSI adapter crashes with CD-ROM (take 2)

On Tue, May 08 2007, Mike Christie wrote:
> James Bottomley wrote:
> > On Tue, 2007-05-08 at 18:14 +0200, Jens Axboe wrote:
> >> On Tue, May 08 2007, Alan Cox wrote:
> >>> The CD-ROM layer doesn't bounce requests for old ISA controllers (and
> >>> nor should it). However they get injected into the SCSI layer via
> >>> sr_ioctl which also doesn't bounce them and SCSI then passes the buffer
> >>> along to a device with unchecked_isa_dma set which either panics or
> >>> truncates the buffer to 24bits.
> >>>
> >>> According to Jens the right long term fix is for the CD layer to route
> >>> the requests differently but in the mean time this has been tested by a
> >>> victim and verified to sort the problem out. For the other 99.9% of users
> >>> it's a no-op and doesn't bounce data.
> >>>
> >>> Signed-off-by: Alan Cox <alan@...hat.com>
> >> Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> >>
> >> Christoph passed me his patch to get rid of ->generic_packet() in the
> >> cdrom layer, so the work is almost complete. This patch is fine as a
> >> work-around until that gets merged, though.
> > 
> > Actually, I think the new scsi request infrastructure should be doing
> > the bouncing (rather than have it done in each problem path we
> > discover).
> > 
> > Mike Christie tells me we're missing bouncing by accident in the
> > scsi_execute path (but not the scsi_execute_async path).  He says this
> > is the fix he proposed:
> > 
> > http://marc.info/?l=linux-scsi&m=115981479822790&w=2
> > 
> 
> Hey Jens and James, one thing I forgot to mention is that I could not
> remember if I needed an extra bio_get in there. I thought I did not
> because the caller is not touching the bio after the bio_endio calls
> like is done with the blk/bio_map_user path. But I did that patch so
> long ago I do not remember now.

If you don't touch it after bio_endio(), then you don't need to hold an
extra reference to it. I'll add your patch.

-- 
Jens Axboe

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