Re: [PATCH] PM / OPP: Protect updates to list_dev with mutex

From: Stephen Boyd
Date: Fri Oct 30 2015 - 13:06:13 EST

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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