At Mon, 19 Jan 2015 10:56:41 +0100,
Jiri Slaby wrote:
>
> There is a race between timer and process contexts. Process context
> does not disable irqs, so when a timer ticks inside process' critical
> section, the system can deadlock. Fix this by a traditional _irqsave
> variant of spin_lock.
>
> [v2] removed ->pointer change as it is called with BH off
Sorry, my previous comment was incorrect. The start function here is
also called from PCM trigger callback that is already irq-disabled.
So, this is also superfluous.
thanks,
Takashi
>
> Signed-off-by: Jiri Slaby <jsl...@suse.cz>
> Cc: Jaroslav Kysela <pe...@perex.cz>
> Cc: Takashi Iwai <ti...@suse.de>
> Cc: alsa-de...@alsa-project.org
> ---
> sound/drivers/dummy.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c
> index d11baaf0f0b4..0791210cb4e7 100644
> --- a/sound/drivers/dummy.c
> +++ b/sound/drivers/dummy.c
> @@ -271,10 +271,13 @@ static void dummy_systimer_update(struct
> dummy_systimer_pcm *dpcm)
> static int dummy_systimer_start(struct snd_pcm_substream *substream)
> {
> struct dummy_systimer_pcm *dpcm = substream->runtime->private_data;
> - spin_lock(&dpcm->lock);
> + unsigned long flags;
> +
> + spin_lock_irqsave(&dpcm->lock, flags);
> dpcm->base_time = jiffies;
> dummy_systimer_rearm(dpcm);
> - spin_unlock(&dpcm->lock);
> + spin_unlock_irqrestore(&dpcm->lock, flags);
> +
> return 0;
> }
>
> --
> 2.2.1
>
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