linux-kernel - Re: [PATCH v1] opp: Release current OPP properly

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Date:   Fri, 13 Aug 2021 09:42:24 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Viresh Kumar <vireshk@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
        Nishanth Menon <nm@...com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v1] opp: Release current OPP properly

On 12-08-21, 13:13, Dmitry Osipenko wrote:
> The current_opp is released only when whole OPP table is released,
> otherwise it's only marked as removed by dev_pm_opp_remove_table().
> Functions like dev_pm_opp_put_clkname() and dev_pm_opp_put_supported_hw()
> are checking whether OPP table is empty and it's not if current_opp is
> set since it holds the refcount of OPP, this produces a noisy warning
> from these functions about busy OPP table. Release current_opp when
> OPP table is removed to fix it.
> 
> Cc: stable@...r.kernel.org
> Fixes: 81c4d8a3c414 ("opp: Keep track of currently programmed OPP")
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/opp/core.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index b335c077f215..73da968b5c86 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -1378,9 +1378,6 @@ static void _opp_table_kref_release(struct kref *kref)
>  	list_del(&opp_table->node);
>  	mutex_unlock(&opp_table_lock);
>  
> -	if (opp_table->current_opp)
> -		dev_pm_opp_put(opp_table->current_opp);
> -
>  	_of_clear_opp_table(opp_table);
>  
>  	/* Release clk */
> @@ -2901,6 +2898,12 @@ void dev_pm_opp_remove_table(struct device *dev)
>  	if (_opp_remove_all_static(opp_table))
>  		dev_pm_opp_put_opp_table(opp_table);
>  
> +	/* Drop reference taken by _find_current_opp() */
> +	if (opp_table->current_opp) {
> +		dev_pm_opp_put(opp_table->current_opp);
> +		opp_table->current_opp = NULL;
> +	}
> +

It is better to drop the reference when the OPP table is really
getting removed.

I think the WARN_ON() in the put_* functions can be dropped. It is
important to check this when the stuff is getting set, like in
dev_pm_opp_set_supported_hw(), but removal is just fine.

-- 
viresh