Patch "cpufreq: Bring CPUs up even if cpufreq_online() failed" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

cpufreq: Bring CPUs up even if cpufreq_online() failed

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
cpufreq-bring-cpus-up-even-if-cpufreq_online-failed.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Chen Yu <[email protected]>
Date: Sun, 9 Apr 2017 13:45:16 +0800
Subject: cpufreq: Bring CPUs up even if cpufreq_online() failed

From: Chen Yu <[email protected]>

commit c4a3fa261b16858416f1fd7db03a33d7ef5fc0b3 upstream.

There is a report that after commit 27622b061eb4 ("cpufreq: Convert to hotplug state machine"), the normal CPU offline/online cycle fails on some platforms.

According to the ftrace result, this problem was triggered on platforms using acpi-cpufreq as the default cpufreq driver, and due to the lack of some ACPI freq method (eg. _PCT), cpufreq_online() failed and returned a negative value, so the CPU hotplug state machine rolled back the CPU online process. Actually, from the user's perspective, the failure of cpufreq_online() should not prevent that CPU from being brought up, although cpufreq might not work on that CPU.

BTW, during system startup cpufreq_online() is not invoked via CPU online but by the cpufreq device creation process, so the APs can be brought up even though cpufreq_online() fails in that stage.

This patch ignores the return value of cpufreq_online/offline() and lets the cpufreq framework deal with the failure. cpufreq_online() itself will do a proper rollback in that case and if _PCT is missing, the ACPI cpufreq driver will print a warning if the corresponding debug options have been enabled.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=194581

---
 drivers/cpufreq/cpufreq.c |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

@@ -2404,6 +2404,20 @@ EXPORT_SYMBOL_GPL(cpufreq_boost_enabled)
  *********************************************************************/
 static enum cpuhp_state hp_online;
 
+static int cpuhp_cpufreq_online(unsigned int cpu)
+{
+	cpufreq_online(cpu);
+
+	return 0;
+}
+
+static int cpuhp_cpufreq_offline(unsigned int cpu)
+{
+	cpufreq_offline(cpu);
+
+	return 0;
+}
+
 /**
  * cpufreq_register_driver - register a CPU Frequency driver
  * @driver_data: A struct cpufreq_driver containing the values#

@@ -2466,8 +2480,8 @@ int cpufreq_register_driver(struct cpufr
 	}
 
 	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "cpufreq:online",
-					cpufreq_online,
-					cpufreq_offline);
+					cpuhp_cpufreq_online,
+					cpuhp_cpufreq_offline);
 	if (ret < 0)
 		goto err_if_unreg;
 	hp_online = ret;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/cpufreq-bring-cpus-up-even-if-cpufreq_online-failed.patch