linux-kernel - Re: [PATCH] cpufreq: exynos5440: Protect opp search calls with rcu lock

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Date:	Mon, 15 Apr 2013 09:10:40 -0500
From:	Nishanth Menon <nm@...com>
To:	Amit Daniel Kachhap <amit.daniel@...sung.com>
Cc:	linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	Kukjin Kim <kgene.kim@...sung.com>,
	lkml <linux-kernel@...r.kernel.org>, cpufreq@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] cpufreq: exynos5440: Protect opp search calls with rcu lock

Daniel,
On Mon, Apr 15, 2013 at 1:24 AM, Amit Daniel Kachhap
<amit.daniel@...sung.com> wrote:
> As per the OPP library documentation(Documentation/power/opp.txt) all
> opp find/get calls should be protected by rcu locks.
>
> Signed-off-by: Amit Daniel Kachhap <amit.daniel@...sung.com>
> ---
>
> This patch is created against linux-next tree and is suggested by
> Nishanth Menon. (https://lkml.org/lkml/2013/4/12/119)
>
>  drivers/cpufreq/exynos5440-cpufreq.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/cpufreq/exynos5440-cpufreq.c b/drivers/cpufreq/exynos5440-cpufreq.c
> index ead7ed4..0c74018 100644
> --- a/drivers/cpufreq/exynos5440-cpufreq.c
> +++ b/drivers/cpufreq/exynos5440-cpufreq.c
> @@ -120,11 +120,13 @@ static int init_div_table(void)
>         int i = 0;
>         struct opp *opp;
>
> +       rcu_read_lock();
>         for (i = 0; freq_tbl[i].frequency != CPUFREQ_TABLE_END; i++) {
>
>                 opp = opp_find_freq_exact(dvfs_info->dev,
>                                         freq_tbl[i].frequency * 1000, true);
>                 if (IS_ERR(opp)) {
> +                       rcu_read_unlock();
>                         dev_err(dvfs_info->dev,
>                                 "failed to find valid OPP for %u KHZ\n",
>                                 freq_tbl[i].frequency);
> @@ -159,6 +161,7 @@ static int init_div_table(void)
>                 __raw_writel(tmp, dvfs_info->base + XMU_PMU_P0_7 + 4 * i);
>         }
>
> +       rcu_read_unlock();

Is it not possible to reduce the amount of code protected by RCU lock?
something like this:
+               rcu_read_lock();
                opp = opp_find_freq_exact(dvfs_info->dev,
                                        freq_tbl[i].frequency * 1000, true);
                if (IS_ERR(opp)) {
+                       rcu_read_unlock();
                        dev_err(dvfs_info->dev,
                                "failed to find valid OPP for %u KHZ\n",
                                freq_tbl[i].frequency);
                        return PTR_ERR(opp);
                }
+               volt_id = opp_get_voltage(opp);
+               rcu_unlock();
--
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