linux-kernel - Re: [PATCH 1/2] ALSA: aloop: Remove redundant locking in timer open function

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Message-ID: <s5hk17r22zh.wl-tiwai@suse.de>
Date:   Fri, 22 Nov 2019 19:13:54 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Andrew Gabbasov <andrew_gabbasov@...tor.com>
Cc:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        "Jaroslav Kysela" <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Timo Wischer <twischer@...adit-jv.com>
Subject: Re: [PATCH 1/2] ALSA: aloop: Remove redundant locking in timer open function

On Fri, 22 Nov 2019 18:52:17 +0100,
Andrew Gabbasov wrote:
> 
> loopback_parse_timer_id() uses snd_card_ref(), that can lock on mutex,
> also snd_timer_instance_new() uses non-atomic allocation, that can sleep.
> So, both functions can not be called from loopback_snd_timer_open()
> with cable->lock spinlock locked.
> 
> Moreover, most part of loopback_snd_timer_open() function body works
> when the opposite stream of the same cable does not yet exist, and
> the current stream is not yet completely open and can't be running,
> so existing locking of loopback->cable_lock mutex is enough to protect
> from conflicts with simultaneous opening or closing.
> Locking of cable->lock spinlock is not needed in this case.
> 
> Fixes: 26c53379f98d ("ALSA: aloop: Support selection of snd_timer instead of jiffies")
> Signed-off-by: Andrew Gabbasov <andrew_gabbasov@...tor.com>

Applied, thanks.


Takashi