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 jslaby@suse.cz Cc: Jaroslav Kysela perex@perex.cz Cc: Takashi Iwai tiwai@suse.de Cc: alsa-devel@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