linux-kernel - Re: [PATCH] opp: Reinitialize the list_kref before adding the static OPPs again

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Message-ID: <20191021021826.afb3yrh2r63mzghw@vireshk-i7>
Date:   Mon, 21 Oct 2019 07:48:26 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] opp: Reinitialize the list_kref before adding the static
 OPPs again

On 18-10-19, 18:35, Dmitry Osipenko wrote:
> 18.10.2019 12:28, Viresh Kumar пишет:
> > The list_kref reaches a count of 0 when all the static OPPs are removed,
> > for example when dev_pm_opp_of_cpumask_remove_table() is called, though
> > the actual OPP table may not get freed as it may still be referenced by
> > other parts of the kernel, like from a call to
> > dev_pm_opp_set_supported_hw(). And if we call
> > dev_pm_opp_of_cpumask_add_table() again at this point, we must
> > reinitialize the list_kref otherwise the kernel will hit a WARN() in
> > kref infrastructure for incrementing a kref with value 0.
> > 
> > Fixes: 11e1a1648298 ("opp: Don't decrement uninitialized list_kref")
> > Reported-by: Dmitry Osipenko <digetx@...il.com>
> > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > ---
> >  drivers/opp/of.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/opp/of.c b/drivers/opp/of.c
> > index 6dc41faf74b5..1cbb58240b80 100644
> > --- a/drivers/opp/of.c
> > +++ b/drivers/opp/of.c
> > @@ -663,6 +663,13 @@ static int _of_add_opp_table_v2(struct device *dev, struct opp_table *opp_table)
> >  		return 0;
> >  	}
> >  
> > +	/*
> > +	 * Re-initialize list_kref every time we add static OPPs to the OPP
> > +	 * table as the reference count may be 0 after the last tie static OPPs
> > +	 * were removed.
> > +	 */
> > +	kref_init(&opp_table->list_kref);
> > +
> >  	/* We have opp-table node now, iterate over it and add OPPs */
> >  	for_each_available_child_of_node(opp_table->np, np) {
> >  		opp = _opp_add_static_v2(opp_table, dev, np);
> > 
> 
> I don't see the warning anymore, cpufreq-dt module reloading works fine
> now. Thank you very much!
> 
> Tested-by: Dmitry Osipenko <digetx@...il.com>

Thanks for testing.

-- 
viresh