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    SubjectRe: [RFC PATCH 13/19] cpufreq: fix locking of policy->rwsem in cpufreq_offline_prepare
    On 11-01-16, 17:35, Juri Lelli wrote:
    > There are paths in cpufreq_offline_prepare where policy is used, but its
    > rwsem is not held.
    >
    > Fix it.
    >
    > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
    > Cc: Viresh Kumar <viresh.kumar@linaro.org>
    > Signed-off-by: Juri Lelli <juri.lelli@arm.com>
    > ---
    > drivers/cpufreq/cpufreq.c | 8 ++++++--
    > 1 file changed, 6 insertions(+), 2 deletions(-)

    I know the locking in general in cpufreq core is poor. We recently
    fixed lots of issues in governors ..

    > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
    > index 2c7cc6c73..91158b0 100644
    > --- a/drivers/cpufreq/cpufreq.c
    > +++ b/drivers/cpufreq/cpufreq.c
    > @@ -1332,13 +1332,13 @@ static void cpufreq_offline_prepare(unsigned int cpu)
    > return;
    > }
    >
    > + down_write(&policy->rwsem);
    > if (has_target()) {
    > int ret = __cpufreq_governor(policy, CPUFREQ_GOV_STOP);
    > if (ret)
    > pr_err("%s: Failed to stop governor\n", __func__);
    > }
    >
    > - down_write(&policy->rwsem);
    > cpumask_clear_cpu(cpu, policy->cpus);
    >
    > if (policy_is_inactive(policy)) {
    > @@ -1356,12 +1356,16 @@ static void cpufreq_offline_prepare(unsigned int cpu)
    > /* Start governor again for active policy */
    > if (!policy_is_inactive(policy)) {

    Why shouldn't this be under the lock?

    > if (has_target()) {
    > - int ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);
    > + int ret;
    > +
    > + down_write(&policy->rwsem);
    > + ret = __cpufreq_governor(policy, CPUFREQ_GOV_START);
    > if (!ret)
    > ret = __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS);
    >
    > if (ret)
    > pr_err("%s: Failed to start governor\n", __func__);
    > + up_write(&policy->rwsem);
    > }
    > } else if (cpufreq_driver->stop_cpu) {
    > cpufreq_driver->stop_cpu(policy);

    And this ?

    --
    viresh

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