Re: [PATCH linux-next v8] cpufreq: convert the cpufreq_driver to use the rcu

From: Rafael J. Wysocki
Date: Sun Apr 28 2013 - 18:14:24 EST

On Thursday, April 04, 2013 09:57:19 PM Viresh Kumar wrote:
> On 4 April 2013 20:23, Nathan Zimmer <nzimmer@xxxxxxx> wrote:
> > We eventually would like to remove the rwlock cpufreq_driver_lock or convert
> > it back to a spinlock and protect the read sections with RCU. The first step in
> > that is moving the cpufreq_driver to use the rcu.
> > I don't see an easy wasy to protect the cpufreq_cpu_data structure with the
> > RCU, so I am leaving it with the rwlock for now since under certain configs
> > __cpufreq_cpu_get is hot spot with 256+ cores.
> >
> > v5: Go a different way and split up the lock and use the rcu
> > v6: use bools instead of checking function pointers
> > covert the cpufreq_data_lock to a rwlock
> > v7: Rebase to use the already accepted half
> > v8: Correct have_governor_per_policy
> > Reviewed location of rcu_read_(un)lock in several spots
> Sorry for long delay or too many versions of this patch :)
> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>

Unfortunately, I had to revert this one, because it is obviously buggy. Why?
Because it adds rcu_read_lock()/rcu_read_unlock() around sysfs_create_file()
which may sleep due to a GFP_KERNEL memory allocation. Sorry for failing to
notice that earlier.


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