From mboxrd@z Thu Jan 1 00:00:00 1970 From: Timo Wischer Subject: Re: [PATCH 04/10] ALSA: aloop: Use always spin_lock_irqsave() for cable->lock Date: Mon, 25 Mar 2019 17:40:23 +0100 Message-ID: <237e2d2d-9a8f-a273-4c40-db2c670c6858@de.adit-jv.com> References: <1553529644-5654-1-git-send-email-twischer@de.adit-jv.com> <1553529644-5654-5-git-send-email-twischer@de.adit-jv.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp1.de.adit-jv.com (smtp1.de.adit-jv.com [93.241.18.167]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id BE0C8F80764 for ; Mon, 25 Mar 2019 17:40:32 +0100 (CET) In-Reply-To: Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" To: Takashi Iwai Cc: alsa-devel@alsa-project.org, broonie@kernel.org, linux-kernel@vger.kernel.org List-Id: alsa-devel@alsa-project.org 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, > wrote: >> From: Timo Wischer >> >> 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? 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) >> 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? Best regards Timo > > > thanks, > > Takashi > > >> Signed-off-by: Timo Wischer >> --- >> 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 >> >>