linux-kernel - Re: cdrom: use kmalloced buffers instead of buffers on stack

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Date:	Mon, 21 Apr 2008 22:01:26 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: cdrom: use kmalloced buffers instead of buffers on stack

Linux Kernel Mailing List wrote:
> Gitweb:     http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=22a9189fd073db3d03a4cf8b8c098aa207602de1
> Commit:     22a9189fd073db3d03a4cf8b8c098aa207602de1
> Parent:     0a0c4114df4a6903bccb65b06cabb6ddc968f877
> Author:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> AuthorDate: Wed Mar 26 12:09:38 2008 +0100
> Committer:  Jens Axboe <jens.axboe@...cle.com>
> CommitDate: Mon Apr 21 09:50:08 2008 +0200
> 
>     cdrom: use kmalloced buffers instead of buffers on stack
>     
>     If cdrom commands are issued to a scsi drive in most cases the buffer will be
>     filled via dma.  This leads to bad stack corruption on non coherent platforms,
>     because the buffers are neither cache line aligned nor is the size a multiple
>     of the cache line size.  Using kmalloced buffers avoids this.
>     
>     Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
>     Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> ---
>  drivers/cdrom/cdrom.c |  274 ++++++++++++++++++++++++++++++++-----------------
>  1 files changed, 181 insertions(+), 93 deletions(-)

Eh... AFAICS this is only really useful in two of the cases converted.

For all the other cases (<= 32 bytes), it is _far_ less complex, far 
less code to simply communicate the additional alignment requirements to 
the compiler.

What about __attribute__ __aligned__?  Was that tried?

	Jeff


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