Race condition in TPA6130A2 (Was: Re: Nokia N900 - audio TPA6130A2 problems)

From: "Pali Rohár" <pali.rohar@gmail.com>
To: Sebastian Reichel <sre@kernel.org>,
	Peter Ujfalusi <peter.ujfalusi@ti.com>,
	Jarkko Nikula <jarkko.nikula@bitmer.com>
Cc: Tony Lindgren <tony@atomide.com>,
	Lars-Peter Clausen <lars@metafoo.de>,
	linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org,
	Pavel Machek <pavel@ucw.cz>, Aaro Koskinen <aaro.koskinen@iki.fi>,
	Nishanth Menon <nm@ti.com>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>,
	merlijn@wizzup.org
Subject: Race condition in TPA6130A2 (Was: Re: Nokia N900 - audio TPA6130A2 problems)
Date: Fri, 1 Apr 2016 12:43:33 +0200	[thread overview]
Message-ID: <20160401104333.GC8413@pali> (raw)
In-Reply-To: <20160316144709.GA3389@earth>

On Wednesday 16 March 2016 15:47:10 Sebastian Reichel wrote:
> I just had another look at the driver and I think there is a race
> condition for tpa6130a2_add_controls() and tpa6130a2_stereo_enable().
> 
> As far as I can see both functions check for "tpa6130a2_client !=
> NULL". tpa6130a2_client is set before the probe function has finished,
> though. Simplified probe:
> 
> ...
> tpa6130a2_client = client;
> set_default_regs();
> acquire_power_gpio();
> acquire_regulator();
> tpa6130a2_power(1); // needs tpa6130a2_client
> check_device();
> tpa6130a2_power(0); // needs tpa6130a2_client
> ...
> 
> If tpa6130a2_add_controls() or tpa6130a2_stereo_enable() is called
> after tpa6130a2 probe has started, but before probe has completed,
> tpa6130a2_client is set, but not yet initialized. The race condition
> can be fixed easily by moving the tpa6130a2_client assignment directly
> after the regulator acquisition.
> 
> -- Sebastian

Is this race condition really relevant? If yes, then it should be fixed.

-- 
Pali Rohár
pali.rohar@gmail.com