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From:   Bo Yan <byan@nvidia.com>
To:     <viresh.kumar@linaro.org>, <rjw@rjwysocki.net>,
        <sgurrappadi@nvidia.com>
CC:     <linux-pm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        Bo Yan <byan@nvidia.com>
Subject: [PATCH] cpufreq: skip cpufreq resume if it's not suspended
Date:   Tue, 23 Jan 2018 13:57:55 -0800
Message-ID: <1516744675-21233-1-git-send-email-byan@nvidia.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
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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 cpufreq_suspended first, if it's false, that means
cpufreq_suspend was not called in the first place, so do not resume
cpufreq.

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

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 41d148af7748..95b1c4afe14e 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1680,6 +1680,10 @@ void cpufreq_resume(void)
 	if (!cpufreq_driver)
 		return;
 
+	if (unlikely(!cpufreq_suspended)) {
+		pr_warn("%s: resume after failing suspend\n", __func__);
+		return;
+	}
 	cpufreq_suspended = false;
 
 	if (!has_target() && !cpufreq_driver->resume)
-- 
2.7.4