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From: Takashi Iwai <tiwai@suse.de>
To: <twischer@de.adit-jv.com>
Cc: <patch@alsa-project.org>, <broonie@kernel.org>, <perex@perex.cz>,
	<alsa-devel@alsa-project.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 09/10] ALSA: pcm: Add snd_pcm_ops for snd_pcm_link()
Date: Tue, 26 Mar 2019 09:35:36 +0100	[thread overview]
Message-ID: <s5ho95ym3s7.wl-tiwai@suse.de> (raw)
In-Reply-To: <1553586574-18608-5-git-send-email-twischer@de.adit-jv.com>

On Tue, 26 Mar 2019 08:49:33 +0100,
<twischer@de.adit-jv.com> wrote:
> 
> From: Timo Wischer <twischer@de.adit-jv.com>
> 
> snd_pcm_link() can be called by the user as long as the device is not
> yet started. Therefore currently a driver which wants to iterate over
> the linked substreams has to do this at the start trigger. But the start
> trigger should not block for a long time. Therefore there is no callback
> which can be used to iterate over the linked substreams without delaying
> the start trigger.
> This patch introduces a new callback function which will be called after
> the linked substream list was updated by snd_pcm_link(). This callback
> function is allowed to block for a longer time without interfering the
> synchronized start up of linked substreams.
> 
> Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>

Well, the idea appears interesting, but I'm afraid that the
implementation is still racy.  The place you're calling the new
callback isn't protected, hence the stream can be triggered while
calling it.  That is, even during operating your loopback link_changed
callback, another thread is able to start the stream.


thanks,

Takashi

WARNING: multiple messages have this Message-ID (diff)
From: Takashi Iwai <tiwai@suse.de>
To: twischer@de.adit-jv.com
Cc: patch@alsa-project.org, broonie@kernel.org, perex@perex.cz,
	alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 09/10] ALSA: pcm: Add snd_pcm_ops for snd_pcm_link()
Date: Tue, 26 Mar 2019 09:35:36 +0100	[thread overview]
Message-ID: <s5ho95ym3s7.wl-tiwai@suse.de> (raw)
In-Reply-To: <1553586574-18608-5-git-send-email-twischer@de.adit-jv.com>

On Tue, 26 Mar 2019 08:49:33 +0100,
<twischer@de.adit-jv.com> wrote:
> 
> From: Timo Wischer <twischer@de.adit-jv.com>
> 
> snd_pcm_link() can be called by the user as long as the device is not
> yet started. Therefore currently a driver which wants to iterate over
> the linked substreams has to do this at the start trigger. But the start
> trigger should not block for a long time. Therefore there is no callback
> which can be used to iterate over the linked substreams without delaying
> the start trigger.
> This patch introduces a new callback function which will be called after
> the linked substream list was updated by snd_pcm_link(). This callback
> function is allowed to block for a longer time without interfering the
> synchronized start up of linked substreams.
> 
> Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>

Well, the idea appears interesting, but I'm afraid that the
implementation is still racy.  The place you're calling the new
callback isn't protected, hence the stream can be triggered while
calling it.  That is, even during operating your loopback link_changed
callback, another thread is able to start the stream.


thanks,

Takashi

  reply	other threads:[~2019-03-26  8:35 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-25 16:00 [PATCH 00/10] ALSA: aloop: Support selection of snd_timer twischer
2019-03-25 16:00 ` twischer
2019-03-25 16:00 ` [PATCH 01/10] ALSA: aloop: Describe units of variables twischer
2019-03-25 16:00   ` twischer
2019-03-25 16:00 ` [PATCH 02/10] ALSA: aloop: loopback_timer_start: Support return of error code twischer
2019-03-25 16:00   ` twischer
2019-03-25 16:00 ` [PATCH 03/10] ALSA: aloop: loopback_timer_stop: " twischer
2019-03-25 16:00   ` twischer
2019-03-25 16:00 ` [PATCH 04/10] ALSA: aloop: Use always spin_lock_irqsave() for cable->lock twischer
2019-03-25 16:00   ` twischer
2019-03-25 16:07   ` Takashi Iwai
2019-03-25 16:07     ` Takashi Iwai
2019-03-25 16:40     ` Timo Wischer
2019-03-25 16:58       ` Takashi Iwai
2019-03-25 16:58         ` Takashi Iwai
2019-03-26  8:12         ` Timo Wischer
2019-03-26  8:12           ` Timo Wischer
2019-03-26  7:49 ` [PATCH 05/10] ALSA: aloop: Use callback functions for timer specific implementations twischer
2019-03-26  7:49   ` twischer
2019-03-26  7:49   ` [PATCH 06/10] ALSA: aloop: Rename all jiffies timer specific functions twischer
2019-03-26  7:49     ` twischer
2019-03-26  7:49   ` [PATCH 07/10] ALSA: aloop: Move CABLE_VALID_BOTH to the top of file twischer
2019-03-26  7:49     ` twischer
2019-03-26  7:49   ` [PATCH 08/10] ALSA: aloop: Support selection of snd_timer instead of jiffies twischer
2019-03-26  7:49     ` twischer
2019-03-26  7:49   ` [PATCH 09/10] ALSA: pcm: Add snd_pcm_ops for snd_pcm_link() twischer
2019-03-26  7:49     ` twischer
2019-03-26  8:35     ` Takashi Iwai [this message]
2019-03-26  8:35       ` Takashi Iwai
2019-03-26 11:25       ` Timo Wischer
2019-03-26 14:23         ` Takashi Iwai
2019-03-26 14:23           ` Takashi Iwai
2019-03-26 15:16           ` Timo Wischer
2019-03-26 15:16             ` Timo Wischer
2019-03-26 16:00             ` Takashi Iwai
2019-03-26 16:00               ` Takashi Iwai
2019-03-27  8:34               ` Timo Wischer
2019-03-27  8:34                 ` Timo Wischer
2019-03-27  9:11                 ` Takashi Iwai
2019-03-27  9:11                   ` Takashi Iwai
2019-03-27  9:26                   ` Timo Wischer
2019-03-27  9:26                     ` Timo Wischer
2019-03-27  9:38                     ` Takashi Iwai
2019-03-27  9:38                       ` Takashi Iwai
2019-04-04 10:18                       ` Timo Wischer
2019-04-04 10:18                         ` Timo Wischer
2019-04-05 15:21                         ` Takashi Iwai
2019-04-05 15:21                           ` Takashi Iwai
2019-03-26  7:52 ` [PATCH 10/10] ALSA: aloop: Use timer of linked card if chosen twischer
2019-03-26  7:52   ` twischer

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