Re: CPUFREQ-CPUHOTPLUG: Possible circular locking dependency

[Ingo Molnar]

* Gautham R Shenoy <ego@xxxxxxxxxx> wrote:

> In process context preemptible code, 
> Lets say we are currently running on processor i.
> 
> cpu_hotplug_lock() ; /* does mutex_lock(&percpu(hotplug_lock, i)) */
> 
> /* do some operation, which might sleep */
> /* migrates to cpu j */
> 
> cpu_hotplug_unlock(); /* does mutex_unlock(&percpu(hotplug_lock, i)
> 			 while running on cpu j */
> 
> This would cause cacheline ping pong, no?

that would be attached to a very cache-inefficient thing: migrating a 
task from one CPU to another. This is not the kind of ping-pong we are 
normally worried about. (nor does it happen all that often)

	Ingo
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