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    Subject[PATCH v2] cpufreq: skip cpufreq resume if it's not suspended
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    cpufreq_resume can be called even without preceding cpufreq_suspend.
    This can happen in following scenario:

    suspend_devices_and_enter
    --> dpm_suspend_start
    --> dpm_prepare
    --> device_prepare : this function errors out
    --> dpm_suspend: this is skipped due to dpm_prepare failure
    this means cpufreq_suspend is skipped over
    --> goto Recover_platform, due to previous error
    --> goto Resume_devices
    --> dpm_resume_end
    --> dpm_resume
    --> cpufreq_resume

    In case schedutil is used as frequency governor, cpufreq_resume will
    eventually call sugov_start, which does following:

    memset(sg_cpu, 0, sizeof(*sg_cpu));
    ....

    This effectively erases function pointer for frequency update, causing
    crash later on. The function pointer would have been set correctly if
    subsequent cpufreq_add_update_util_hook runs successfully, but that
    function returns earlier because cpufreq_suspend was not called:

    if (WARN_ON(per_cpu(cpufreq_update_util_data, cpu)))
    return;

    Ideally, suspend should succeed, then things will be fine. But even
    in case of suspend failure, system should not crash.

    The fix is to check the pm_transition status in dpm_resume. if
    pm_transition.event == PMSG_ON, we know for sure dpm_suspend has not
    been called, so do not call cpufreq_resume.

    Signed-off-by: Bo Yan <byan@nvidia.com>
    ---
    drivers/base/power/main.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
    index 08744b572af6..39829d7a9311 100644
    --- a/drivers/base/power/main.c
    +++ b/drivers/base/power/main.c
    @@ -921,6 +921,7 @@ static void async_resume(void *data, async_cookie_t cookie)
    void dpm_resume(pm_message_t state)
    {
    struct device *dev;
    + bool suspended = (pm_transition.event != PM_EVENT_ON);
    ktime_t starttime = ktime_get();

    trace_suspend_resume(TPS("dpm_resume"), state.event, true);
    @@ -964,7 +965,8 @@ void dpm_resume(pm_message_t state)
    async_synchronize_full();
    dpm_show_time(starttime, state, 0, NULL);

    - cpufreq_resume();
    + if (likely(suspended))
    + cpufreq_resume();
    trace_suspend_resume(TPS("dpm_resume"), state.event, false);
    }

    --
    2.7.4
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