linux-kernel - Re: [PATCH] PM / OPP: Protect updates to list

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Date:	Fri, 30 Oct 2015 10:06:04 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Rafael Wysocki <rjw@...ysocki.net>, mturquette@...libre.com,
	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Dmitry Torokhov <dtor@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Len Brown <len.brown@...el.com>,
	open list <linux-kernel@...r.kernel.org>,
	Nishanth Menon <nm@...com>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

On 10/30, Viresh Kumar wrote:
> dev_opp_list_lock is used everywhere to protect device and OPP lists,
> but dev_pm_opp_set_sharing_cpus() is missed somehow. And instead we used
> rcu-lock, which wouldn't help here as we are adding a new list_dev.
> 
> This also fixes a problem where we have called kzalloc(..., GFP_KERNEL)
> from within rcu-lock, which isn't allowed as kzalloc can sleep when
> called with GFP_KERNEL.

Care to share the splat here?

> diff --git a/drivers/base/power/opp/cpu.c b/drivers/base/power/opp/cpu.c
> index 7654c5606307..91f15b2e25ee 100644
> --- a/drivers/base/power/opp/cpu.c
> +++ b/drivers/base/power/opp/cpu.c
> @@ -124,12 +124,12 @@ int dev_pm_opp_set_sharing_cpus(struct device *cpu_dev, cpumask_var_t cpumask)
>  	struct device *dev;
>  	int cpu, ret = 0;
>  
> -	rcu_read_lock();
> +	mutex_lock(&dev_opp_list_lock);
>  
>  	dev_opp = _find_device_opp(cpu_dev);

So does _find_device_opp() need to be called with rcu_read_lock()
held or not? The comment above the function makes it sound like
we need RCU, but we don't do that here anymore.

-- 
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