Messages in this thread |  | | | Date | Tue, 22 Apr 2008 07:48:58 +0200 | | Subject | Re: cdrom: use kmalloced buffers instead of buffers on stack | | From | (Thomas Bogendoerfer) | |
On Mon, Apr 21, 2008 at 10:01:26PM -0400, Jeff Garzik wrote:
> > 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@alpha.franken.de>
> > Signed-off-by: Jens Axboe <jens.axboe@oracle.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?
I used that while narrowing down the bug. But not only the alignment is
important, but also size needs to be a multiple of the cache line size.
Which means it needs to be 128 bytes for most SGI machines. That
and the following in DMA-mapping.txt
"This rule also means that you may use neither kernel image addresses
(items in data/text/bss segments), nor module image addresses, nor
stack addresses for DMA."
let me choose the kmalloc() solution.
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessary a
good idea. [ RFC1925, 2.3 ]
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