Messages in this thread | | | Date | Tue, 22 Apr 2008 08:33:33 +0200 | From | Jens Axboe <> | Subject | Re: cdrom: use kmalloced buffers instead of buffers on stack |
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On Tue, Apr 22 2008, Thomas Bogendoerfer wrote: > 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.
Which is good, the patch has been due for years :-)
-- Jens Axboe
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