On Mon, 25 Mar 2019 17:40:23 +0100, Timo Wischer wrote: > > Best regards > Timo Wischer > Engineering Software Base (ADITG/ESB) > > Tel. +49 5121 49 6938 > On 3/25/19 17:07, Takashi Iwai wrote: > > On Mon, 25 Mar 2019 17:00:38 +0100, > <twischer@xxxxxxxxxxxxxx> wrote: > > From: Timo Wischer <twischer@xxxxxxxxxxxxxx> > > to allow the usage of timer callbacks from interrupt context. > For example the sound timer. > > The trigger callback is already irq-disabled. And, open/close must > not be irq-disabled OTOH. So these changes must be superfluous. > > Hello Takashi, > > could you explain why open/close must not be irq-disabled? The open/close callbacks get called always in sleepable context where you can use mutex & co gracefully. The only non-sleepable (atomic) context is pointer and trigger callbacks. So it's safe to use spin_lock() without irq in these callbacks. OTOH, the rest (open, close,hw_params, hw_free, prepare) callbacks are always sleepable, hence it's safe to use spin_lock_irq() (not save/restore) variant. When a driver declares as non-atomic via PCM flag, all callbacks become sleepable, but this isn't the case for aloop driver. > I see a potential deadlock in case of free_cable() uses only spin_lock() > instead of spin_lock_irqsave(). > For example the following will be executed: > > loopback_close() > free_cable() > spin_lock(&dpcm->cable->lock) Which spin_lock() call? The free_cable() calls spin_lock_irq(). > >> Interrupted by jiffies timer IRQ before calling spin_unlock() > > loopback_jiffies_timer_function() > spin_lock_irqsave(&dpcm->cable->lock) > >> DEADLOCK due to dpcm->cable->lock is already locked > > Do you also see this deadlock or do you see any reason why this could not > happen? If spin_lock_irq() is used in free_cable(), it must be OK. Takashi > Best regards > > Timo > > thanks, > > Takashi > > Signed-off-by: Timo Wischer <twischer@xxxxxxxxxxxxxx> > --- > sound/drivers/aloop.c | 33 +++++++++++++++++++-------------- > 1 file changed, 19 insertions(+), 14 deletions(-) > > diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c > index 11e8ed6..c6217c4 100644 > --- a/sound/drivers/aloop.c > +++ b/sound/drivers/aloop.c > @@ -272,6 +272,7 @@ static int loopback_trigger(struct snd_pcm_substream *substream, int cmd) > struct loopback_pcm *dpcm = runtime->private_data; > struct loopback_cable *cable = dpcm->cable; > int err = 0, stream = 1 << substream->stream; > + unsigned long flags; > > switch (cmd) { > case SNDRV_PCM_TRIGGER_START: > @@ -281,39 +282,39 @@ static int loopback_trigger(struct snd_pcm_substream *substream, int cmd) > dpcm->last_jiffies = jiffies; > dpcm->pcm_rate_shift = 0; > dpcm->last_drift = 0; > - spin_lock(&cable->lock); > + spin_lock_irqsave(&cable->lock, flags); > cable->running |= stream; > cable->pause &= ~stream; > err = loopback_timer_start(dpcm); > - spin_unlock(&cable->lock); > + spin_unlock_irqrestore(&cable->lock, flags); > if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) > loopback_active_notify(dpcm); > break; > case SNDRV_PCM_TRIGGER_STOP: > - spin_lock(&cable->lock); > + spin_lock_irqsave(&cable->lock, flags); > cable->running &= ~stream; > cable->pause &= ~stream; > err = loopback_timer_stop(dpcm); > - spin_unlock(&cable->lock); > + spin_unlock_irqrestore(&cable->lock, flags); > if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) > loopback_active_notify(dpcm); > break; > case SNDRV_PCM_TRIGGER_PAUSE_PUSH: > case SNDRV_PCM_TRIGGER_SUSPEND: > - spin_lock(&cable->lock); > + spin_lock_irqsave(&cable->lock, flags); > cable->pause |= stream; > err = loopback_timer_stop(dpcm); > - spin_unlock(&cable->lock); > + spin_unlock_irqrestore(&cable->lock, flags); > if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) > loopback_active_notify(dpcm); > break; > case SNDRV_PCM_TRIGGER_PAUSE_RELEASE: > case SNDRV_PCM_TRIGGER_RESUME: > - spin_lock(&cable->lock); > + spin_lock_irqsave(&cable->lock, flags); > dpcm->last_jiffies = jiffies; > cable->pause &= ~stream; > err = loopback_timer_start(dpcm); > - spin_unlock(&cable->lock); > + spin_unlock_irqrestore(&cable->lock, flags); > if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) > loopback_active_notify(dpcm); > break; > @@ -557,12 +558,13 @@ static snd_pcm_uframes_t loopback_pointer(struct snd_pcm_substream *substream) > { > struct snd_pcm_runtime *runtime = substream->runtime; > struct loopback_pcm *dpcm = runtime->private_data; > + unsigned long flags; > snd_pcm_uframes_t pos; > > - spin_lock(&dpcm->cable->lock); > + spin_lock_irqsave(&dpcm->cable->lock, flags); > loopback_pos_update(dpcm->cable); > pos = dpcm->buf_pos; > - spin_unlock(&dpcm->cable->lock); > + spin_unlock_irqrestore(&dpcm->cable->lock, flags); > return bytes_to_frames(runtime, pos); > } > > @@ -679,10 +681,12 @@ static void free_cable(struct snd_pcm_substream *substream) > if (!cable) > return; > if (cable->streams[!substream->stream]) { > + unsigned long flags; > + > /* other stream is still alive */ > - spin_lock_irq(&cable->lock); > + spin_lock_irqsave(&cable->lock, flags); > cable->streams[substream->stream] = NULL; > - spin_unlock_irq(&cable->lock); > + spin_unlock_irqrestore(&cable->lock, flags); > } else { > /* free the cable */ > loopback->cables[substream->number][dev] = NULL; > @@ -698,6 +702,7 @@ static int loopback_open(struct snd_pcm_substream *substream) > struct loopback_cable *cable = NULL; > int err = 0; > int dev = get_cable_index(substream); > + unsigned long flags; > > mutex_lock(&loopback->cable_lock); > dpcm = kzalloc(sizeof(*dpcm), GFP_KERNEL); > @@ -753,9 +758,9 @@ static int loopback_open(struct snd_pcm_substream *substream) > else > runtime->hw = cable->hw; > > - spin_lock_irq(&cable->lock); > + spin_lock_irqsave(&cable->lock, flags); > cable->streams[substream->stream] = dpcm; > - spin_unlock_irq(&cable->lock); > + spin_unlock_irqrestore(&cable->lock, flags); > > unlock: > if (err < 0) { > -- > 2.7.4 > > _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel