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Date:   Tue, 13 Jun 2023 15:01:02 +0200
From:   Stephan Gerhold <stephan.gerhold@kernkonzept.com>
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
        Stephen Boyd <sboyd@kernel.org>, linux-pm@vger.kernel.org,
        Vincent Guittot <vincent.guittot@linaro.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] OPP: Protect `lazy_opp_tables` list with
 `opp_table_lock`
Message-ID: <ZIhojuakyEUct7YN@kernkonzept.com>
References: <167eb2bd947d9c04b0f6f1a5495ce4a99eeab598.1686210112.git.viresh.kumar@linaro.org>
 <c0bac65236cf77fa8ac17c2645449544b73a0104.1686210112.git.viresh.kumar@linaro.org>
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On Thu, Jun 08, 2023 at 01:13:23PM +0530, Viresh Kumar wrote:
> The `opp_table_lock` lock is already used to protect the list elsewhere,
> use it while adding or removing entries from it.
> 
> Reported-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> Stephan: Can you please give this a try ?

Thanks, works fine for me. (Note that I don't have any races or
corruption without this patch either so the testing result might
not mean too much.) The patch also looks good!

Tested-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>

> 
>  drivers/opp/of.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/opp/of.c b/drivers/opp/of.c
> index c740a907ef76..ac2179d5da4c 100644
> --- a/drivers/opp/of.c
> +++ b/drivers/opp/of.c
> @@ -21,7 +21,7 @@
>  
>  #include "opp.h"
>  
> -/* OPP tables with uninitialized required OPPs */
> +/* OPP tables with uninitialized required OPPs, protected by opp_table_lock */
>  static LIST_HEAD(lazy_opp_tables);
>  
>  /*
> @@ -148,7 +148,10 @@ static void _opp_table_free_required_tables(struct opp_table *opp_table)
>  
>  	opp_table->required_opp_count = 0;
>  	opp_table->required_opp_tables = NULL;
> +
> +	mutex_lock(&opp_table_lock);
>  	list_del(&opp_table->lazy);
> +	mutex_unlock(&opp_table_lock);
>  }
>  
>  /*
> @@ -197,8 +200,15 @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
>  	}
>  
>  	/* Let's do the linking later on */
> -	if (lazy)
> +	if (lazy) {
> +		/*
> +		 * The OPP table is not held while allocating the table, take it
> +		 * now to avoid corruption to the lazy_opp_tables list.
> +		 */
> +		mutex_lock(&opp_table_lock);
>  		list_add(&opp_table->lazy, &lazy_opp_tables);
> +		mutex_unlock(&opp_table_lock);
> +	}
>  	else
>  		_update_set_required_opps(opp_table);
>  
> -- 
> 2.31.1.272.g89b43f80a514
> 

-- 
Stephan Gerhold
Kernkonzept GmbH at Dresden, Germany, HRB 31129, CEO Dr.-Ing. Michael Hohmuth