[PATCH v2] ARM: pl330: Fix a race condition

[Thomas Abraham]

Hi Javi,

On 6 October 2011 05:10, Javi Merino <javi.merino at arm.com> wrote:
> If two requests have been submitted and one of them is running, if you
> call pl330_chan_ctrl(ch_id, PL330_OP_START), there's a window of time
> between the spin_lock_irqsave() and the _state() check in which the
> running transaction may finish.  In that case, we don't receive the
> interrupt (because they are disabled), but _start() sees that the DMA
> is stopped, so it starts it.  The problem is that it sends the
> transaction that has just finished again, because pl330_update()
> hasn't mark it as done yet.
>
> This patch fixes this race condition by not calling _start() if the
> DMA is already executing transactions.  When interrupts are reenabled,
> pl330_update() will call _start().
>
> Signed-off-by: Javi Merino <javi.merino at arm.com>
> Acked-by: Jassi Brar <jassi.brar at samsung.com>
> ---
>  arch/arm/common/pl330.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/arm/common/pl330.c b/arch/arm/common/pl330.c
> index 97912fa..7129cfb 100644
> --- a/arch/arm/common/pl330.c
> +++ b/arch/arm/common/pl330.c
> @@ -1546,7 +1546,7 @@ int pl330_chan_ctrl(void *ch_id, enum pl330_chan_op op)
>
>                /* Start the next */
>        case PL330_OP_START:
> -               if (!_start(thrd))
> +               if (!_thrd_active(thrd) && !_start(thrd))
>                        ret = -EIO;
>                break;

On Samsung's Exynos4 platform, while testing audio playback with i2s
interface, the above change causes the playback to freeze. The
_thrd_active(thrd) call always returns '1' and hence _start(thrd) is
not getting called.

I have not debugged this much but if there is something that I am
missing, please let me know. Meanwhile, I will continue checking on
this.

Thanks,
Thomas.


>
> --
> 1.7.0.4
>
>
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