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SubjectRE: [PATCH 2/2] dma/ep93xx_dma: prevent ep93xx_dma_tasklet() to access empty list
On Tuesday, November 22, 2011 12:46 PM, Mika Westerberg wrote:
> From: Rafal Prylowski <prylowski@metasoft.pl>
>
> If dma_terminate_all() is called before the ep93xx_dma_tasklet() gets to run,
> it tries to access an empty ->active list causing following OOPS:

[snip]

> As we expect that the ->active list is never empty when the ep93xx_dma_tasklet()
> is called, we fix this by adding a new flag per channel EP93XX_DMA_IS_RUNNING
> which determines whether the channel is running or not.
>
> We also add BUG_ON() to ep93xx_dma_get_active() to make sure that similar
> problems will be caught early.
>
> Signed-off-by: Rafal Prylowski <prylowski@metasoft.pl>
> [added a flag instead of just checking for empty list]
> Signed-off-by: Mika Westerberg <mika.westerberg@iki.fi>
> ---
> drivers/dma/ep93xx_dma.c | 25 ++++++++++++++++---------
> 1 files changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/dma/ep93xx_dma.c b/drivers/dma/ep93xx_dma.c
> index 6181811..cc3a302 100644
> --- a/drivers/dma/ep93xx_dma.c
> +++ b/drivers/dma/ep93xx_dma.c
> @@ -155,6 +155,8 @@ struct ep93xx_dma_chan {
> unsigned long flags;
> /* Channel is configured for cyclic transfers */
> #define EP93XX_DMA_IS_CYCLIC 0
> +/* Channel is enabled */
> +#define EP93XX_DMA_IS_RUNNING 1
>
> int buffer;
> dma_cookie_t last_completed;
> @@ -246,6 +248,7 @@ static void ep93xx_dma_set_active(struct ep93xx_dma_chan *edmac,
> static struct ep93xx_dma_desc *
> ep93xx_dma_get_active(struct ep93xx_dma_chan *edmac)
> {
> + BUG_ON(list_empty(&edmac->active));
> return list_first_entry(&edmac->active, struct ep93xx_dma_desc, node);

Mika,

Thanks for looking into this.

I still don't like the BUG_ON here. Is it even possible to get here with
an empty list now that your catching it in the tasklet?

But, ep93xx_dma_set_active() also has a BUG_ON test so...

Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>


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