On 3/25/19 17:58, Takashi Iwai wrote:
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@de.adit-jv.com> wrote: From: Timo Wischer <twischer@de.adit-jv.com> 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
Thanks for the detailed explanation.
@all: Please simple ignore this patch.
Best regards
Timo
Best regards
Timo
thanks, Takashi Signed-off-by: Timo Wischer <twischer@de.adit-jv.com> --- 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