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SubjectRe: [PATCH] libata: don't initialize sg in ata_exec_internal() if DMA_NONE
Tejun Heo wrote:
> Calling sg_init_one() with NULL buf causes oops on certain
> configurations. Don't initialize sg in ata_exec_internal() if
> DMA_NONE and make the function complain if @buf is NULL when dma_dir
> isn't DMA_NONE. While at it, fix comment.
>
> The problem is discovered and initial patch was submitted by Arnd
> Bergmann.
>
> Signed-off-by: Tejun Heo <htejun@gmail.com>
> Cc: Arnd Bergmann <arnd.bergmann@de.ibm.com>
> ---
>
> Hello, Arnd Bergmann.
>
> Thanks for spotting and fixing this but ata_exec_internal_nodma() is
> almost identical to ata_do_simple_cmd() and ata_exec_internal() itself
> needs fixing anyway. This patch just fixes ata_exec_internal(). I'll
> follow up with conversion to ata_do_simple_cmd().
>
> Thanks.
>
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index 011c0a8..70e02e9 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -1332,7 +1332,7 @@ unsigned ata_exec_internal_sg(struct ata_device *dev,
> }
>
> /**
> - * ata_exec_internal_sg - execute libata internal command
> + * ata_exec_internal - execute libata internal command
> * @dev: Device to which the command is sent
> * @tf: Taskfile registers for the command and the result
> * @cdb: CDB for packet command
> @@ -1354,10 +1354,15 @@ unsigned ata_exec_internal(struct ata_device *dev,
> int dma_dir, void *buf, unsigned int buflen)
> {
> struct scatterlist sg;
> + unsigned int n_elem = 0;
>
> - sg_init_one(&sg, buf, buflen);
> + if (dma_dir != DMA_NONE) {
> + WARN_ON(!buf);
> + sg_init_one(&sg, buf, buflen);
> + n_elem++;
> + }
>
> - return ata_exec_internal_sg(dev, tf, cdb, dma_dir, &sg, 1);
> + return ata_exec_internal_sg(dev, tf, cdb, dma_dir, &sg, n_elem);

ACK, if you conditionally replace "&sg" with NULL. That's the safer
choice, as it guarantees (via an oops) that the user will not be
touching sg, if dma_dir==DMA_NONE.

Jeff



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