[alsa-devel] [PATCH] ASoC: core: Fix race in dapm_power_widgets

[Liam Girdwood]

On Thu, 2010-11-04 at 10:16 +0200, Peter Ujfalusi wrote:
> dapm_power_widgets can be called from different context.
> When two calls are happening at the same time both will
> try to change states/lists. This can lead to kernel crash.
> 
> A simple way to reproduce the problem:
> 
> while [ "1" = "1" ] ; do
> amixer sset -Dhw:0 -q 'Mixer for loopback' on
> amixer sset -Dhw:0 -q 'Mixer for loopback' off
> done &
> 
> while [ "1" = "1" ] ; do
> aplay -Dplughw:0 -fdat -d 3 /dev/urandom
> echo "Playback finished"
> sleep 6
> done &
> 
> Add new card level mutex (dpw_mutex) to protect the
> dapm_power_widgets from race.
> The exisiting card->mutex can not be used for this purpose,
> since it has been taken in probe time in the
> snd_soc_instantiate_card function. Through probe calls from
> this function eventually dapm_power_widgets will be called,
> which will lead to dead lock.
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi at nokia.com>

Acked-by: Liam Girdwood <lrg at slimlogic.co.uk>
-- 
Freelance Developer, SlimLogic Ltd
ASoC and Voltage Regulator Maintainer.
http://www.slimlogic.co.uk