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SubjectRe: [BUG][2.6.38] IRQ Lock Inversion / i915 fails
At Thu, 17 Mar 2011 09:55:47 -0700,
Linus Torvalds wrote:
>
> On Thu, Mar 17, 2011 at 2:40 AM, Knut Petersen
> <Knut_Petersen@t-online.de> wrote:
> >
> > Well, I updated my test partition to opensuse 11.4.
> >
> > The opensuse standard kernel is unusable for me, booting hangs
> > most of the time, the same is true for shutdown. If booting succeeds the
> > system will fail after a short time of usage.
> >
> > So I installed kernel 2.6.38.  That helped a lot ... for a few minutes.
> >
> > A possible irq lock inversion is detected during boot, after a short time
> > X fails, restarting the X server does not work, a reboot is necessary.
>
> Ok, so the lock inversion seems to be due to the sound/drivers/aloop.c
> file, where the function "loopback_pos_update()" gets called from
> within a softirq context. And it takes a lock (cable->lock) that is
> also taken unprotected by loopback_trigger(). So that's liable to
> deadlock as per lockdep. Jaroslav? Takashi?

The trigger callback should be called always in irq-disabled context,
so this should be OK. But loopback_pos_update() is called in the
timer callback, and this can be the issue.

Knut, how about the patch below?


thanks,

Takashi

---
diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
index 12b44b0..a0da775 100644
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -482,8 +482,9 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
cable->streams[SNDRV_PCM_STREAM_CAPTURE];
unsigned long delta_play = 0, delta_capt = 0;
unsigned int running;
+ unsigned long flags;

- spin_lock(&cable->lock);
+ spin_lock_irqsave(&cable->lock, flags);
running = cable->running ^ cable->pause;
if (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) {
delta_play = jiffies - dpcm_play->last_jiffies;
@@ -495,10 +496,8 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
dpcm_capt->last_jiffies += delta_capt;
}

- if (delta_play == 0 && delta_capt == 0) {
- spin_unlock(&cable->lock);
- return running;
- }
+ if (delta_play == 0 && delta_capt == 0)
+ goto unlock;

if (delta_play > delta_capt) {
loopback_bytepos_update(dpcm_play, delta_play - delta_capt,
@@ -510,14 +509,14 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
delta_capt = delta_play;
}

- if (delta_play == 0 && delta_capt == 0) {
- spin_unlock(&cable->lock);
- return running;
- }
+ if (delta_play == 0 && delta_capt == 0)
+ goto unlock;
+
/* note delta_capt == delta_play at this moment */
loopback_bytepos_update(dpcm_capt, delta_capt, BYTEPOS_UPDATE_COPY);
loopback_bytepos_update(dpcm_play, delta_play, BYTEPOS_UPDATE_POSONLY);
- spin_unlock(&cable->lock);
+ unlock:
+ spin_unlock_irqrestore(&cable->lock, flags);
return running;
}

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