Re: [RFC] opp: Fixup release of clock when using set/put clkname

[Rajendra Nayak]

On 4/14/2020 12:48 PM, Viresh Kumar wrote:
> On 14-04-20, 12:45, Rajendra Nayak wrote:
> > Fixup dev_pm_opp_put_clkname() to check for a valid clock pointer
> > before it does a clk_put, since its likely that
> > _opp_table_kref_release() has already done a clk_put. Also fixup
>
> kref release is the last thing that happens on the table, it can't get
> called after dev_pm_opp_put_clkname().

so in cases where I do have an OPP table for a device in DT and I do
dev_pm_opp_set_clkname()
dev_pm_opp_of_add_table()

and clean it up with a
dev_pm_opp_of_remove_table()
dev_pm_opp_put_clkname()

things seem to work fine as expected.

However, given I call these unconditionally in common drivers and on
some (old) platforms we really don't have an OPP table (only scale clocks)
things get a little tricky. So looks like the ref counting in such cases
gets messed up, and we end up with dev_pm_opp_of_remove_table() calling
_opp_table_kref_release() and releasing the clock, and then the subsequent
call to dev_pm_opp_put_clkname() crashes.

> > _opp_table_kref_release() to set the clock pointer to ERR_PTR(-EINVAL)
> > after its done doing a clk_put so dev_pm_opp_put_clkname() can then
> > catch it.
> >
> > Signed-off-by: Rajendra Nayak <rnayak@xxxxxxxxxxxxxx>
> > ---
> >   drivers/opp/core.c | 10 +++++++---
> >   1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> > index e4f01e7..6d064a8 100644
> > --- a/drivers/opp/core.c
> > +++ b/drivers/opp/core.c
> > @@ -1061,8 +1061,10 @@ static void _opp_table_kref_release(struct kref *kref)
> >   	_of_clear_opp_table(opp_table);
> >   
> >   	/* Release clk */
> > -	if (!IS_ERR(opp_table->clk))
> > +	if (!IS_ERR(opp_table->clk)) {
> >   		clk_put(opp_table->clk);
> > +		opp_table->clk = ERR_PTR(-EINVAL);
> > +	}
> >   
> >   	WARN_ON(!list_empty(&opp_table->opp_list));
> >   
> > @@ -1744,8 +1746,10 @@ void dev_pm_opp_put_clkname(struct opp_table *opp_table)
> >   	/* Make sure there are no concurrent readers while updating opp_table */
> >   	WARN_ON(!list_empty(&opp_table->opp_list));
> >   
> > -	clk_put(opp_table->clk);
> > -	opp_table->clk = ERR_PTR(-EINVAL);
> > +	if (!IS_ERR(opp_table->clk)) {
> > +		clk_put(opp_table->clk);
> > +		opp_table->clk = ERR_PTR(-EINVAL);
> > +	}
> >   
> >   	dev_pm_opp_put_opp_table(opp_table);
> >   }
> > --
> > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> > of Code Aurora Forum, hosted by The Linux Foundation

--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation