On 09/29/2014 09:06 PM, Sebastian Andrzej Siewior wrote:
> I added book keeping of whether or not the 8250-dma driver has an RX
> transfer pending or not so we don't BUG here if it calls
> dmaengine_pause() on a channel which has not a pending transfer. Guess
> what, this is not enough.
> The following can be triggered with a busy RX channel and hackbench in
> background:
> - DMA transfer completes. The callback is delayed via
> vchan_cookie_complete() into a tasklet so it das not happen asap.
> - hackbench keeps the system busy so the tasklet does not run "soon".
> - the UART collected enough data and generates an "timeout"-interrupt.
> Since 8250-dma *thinks* the DMA-transfer is still pending it tries to
> cancel it via invoking dmaengine_pause() first. This causes the segfault
> because echan->edesc is NULL now that the transfer completed (however
> the callback did not run yet).
>
> With this patch we don't BUG in the scenario described.
Acked-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx>
>
> Cc: vinod.koul@xxxxxxxxx
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> drivers/dma/edma.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
> index 7b65633f495e..123f578d6dd3 100644
> --- a/drivers/dma/edma.c
> +++ b/drivers/dma/edma.c
> @@ -288,7 +288,7 @@ static int edma_slave_config(struct edma_chan *echan,
> static int edma_dma_pause(struct edma_chan *echan)
> {
> /* Pause/Resume only allowed with cyclic mode */
> - if (!echan->edesc->cyclic)
> + if (!echan->edesc || !echan->edesc->cyclic)
> return -EINVAL;
>
> edma_pause(echan->ch_num);
>
--
Péter
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