linux-kernel - Re: [PATCH 1/2] PM / OPP: Assert RCU lock in exported functions

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Message-ID: <2257225.Zj8XFux8qJ@vostro.rjw.lan>
Date:	Fri, 30 Jan 2015 01:16:33 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] PM / OPP: Assert RCU lock in exported functions

On Friday, January 09, 2015 09:27:57 AM Krzysztof Kozlowski wrote:
> Add lockdep asserts for holding the RCU lock when calling
> dev_pm_opp_get_freq() and dev_pm_opp_get_voltage() to aid in detecting
> RCU misuses.
> 
> These are called often after dev_pm_opp_find_freq_ceil/exact() which
> already asserts for RCU lock. However one could make an error by
> releasing lock too early - just after dev_pm_opp_find_freq_ceil().
> 
> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>

Queued up for 3.20, thanks!

> ---
>  drivers/base/power/opp.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> index 106c69359306..842d31e24eee 100644
> --- a/drivers/base/power/opp.c
> +++ b/drivers/base/power/opp.c
> @@ -169,6 +169,8 @@ unsigned long dev_pm_opp_get_voltage(struct dev_pm_opp *opp)
>  	struct dev_pm_opp *tmp_opp;
>  	unsigned long v = 0;
>  
> +	opp_rcu_lockdep_assert();
> +
>  	tmp_opp = rcu_dereference(opp);
>  	if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
>  		pr_err("%s: Invalid parameters\n", __func__);
> @@ -199,6 +201,8 @@ unsigned long dev_pm_opp_get_freq(struct dev_pm_opp *opp)
>  	struct dev_pm_opp *tmp_opp;
>  	unsigned long f = 0;
>  
> +	opp_rcu_lockdep_assert();
> +
>  	tmp_opp = rcu_dereference(opp);
>  	if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
>  		pr_err("%s: Invalid parameters\n", __func__);
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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