[BUG] v4.11-rc1: CPUFREQ Circular locking dependency

[Zhang Rui]

On Wed, 2017-03-29 at 18:51 +0100, Russell King - ARM Linux wrote:
> On Mon, Mar 13, 2017 at 10:44:48AM +0800, Zhang Rui wrote:
> > 
> > On Fri, 2017-03-10 at 23:43 +0000, Russell King - ARM Linux wrote:
> > > 
> > > On Fri, Mar 10, 2017 at 06:33:28PM +0000, Matthew Wilcox wrote:
> > > > 
> > > > 
> > > > From cd5401d81633d5e48e39d67d4e65156e6759537e Mon Sep 17
> > > > 00:00:00
> > > > 2001
> > > > From: Matthew Wilcox <mawilcox at microsoft.com>
> > > > Date: Fri, 10 Mar 2017 13:22:53 -0500
> > > > Subject: [PATCH] thermal: Fix potential deadlock in cpu_cooling
> > > > 
> > > > I expanded the scope of cooling_list_lock a little too far; it
> > > > was
> > > > not just covering cpufreq_dev_count, it was also covering the
> > > > calls
> > > > to cpufreq_register_notifier() and
> > > > cpufreq_unregister_notifier().
> > > > Since cooling_list_lock is also used within
> > > > cpufreq_thermal_notifier(),
> > > > lockdep reports a potential deadlock.  I don't think that's
> > > > actually
> > > > possible, but it's easy enough to make it impossible by testing
> > > > the
> > > > condition under cooling_list_lock and dropping the lock before
> > > > calling
> > > > cpufreq_register_notifier().
> > > > 
> > > > As a bonus, I noticed that cpufreq_dev_count is only used for
> > > > the
> > > > purpose
> > > > of knowing whether this is the first or last cooling device
> > > > registered,
> > > > and we know that anyway because we know whether the list
> > > > transitioned
> > > > between empty and not-empty.  So we can delete that variable
> > > > too.
> > > > 
> > > > Fixes: ae606089621ef0349402cfcbeca33a82abbd0fd0
> > > > Reported-by: Russell King <linux at armlinux.org.uk>
> > > > Signed-off-by: Matthew Wilcox <mawilcox at microsoft.com>
> > > Thanks Matthew, appears to solve the problem.
> > > 
> > > Tested-by: Russell King <rmk+kernel at armlinux.org.uk>
> > > 
> > patch applied.
> It's almost three weeks, and it isn't in Linus' tree.  What's
> happening
> with this _fix_ for a regression that occured during the merge
> window?
> 
Pull request just sent out, thanks for the reminder.

-rui