[PATCH] hwmon: (coretemp) Handle frozen hotplug state correctly

[Thomas Gleixner]

The recent conversion to the hotplug state machine missed that the original
hotplug notifiers did not execute in the frozen state, which is used on
suspend on resume.

This does not matter on single socket machines, but on multi socket systems
this breaks when the device for a non-boot socket is removed when the last
CPU of that socket is brought offline. The device removal locks up the
machine hard w/o any debug output.

Prevent executing the hotplug callbacks when cpuhp_tasks_frozen is true.

Thanks to Tommi for providing debug information patiently while I failed to
spot the obvious.

Fixes: e00ca5df37ad ("hwmon: (coretemp) Convert to hotplug state machine")
Reported-by: Tommi Rantala <tt.rantala@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 drivers/hwmon/coretemp.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -605,6 +605,13 @@ static int coretemp_cpu_online(unsigned
 	struct platform_data *pdata;
 
 	/*
+	 * Don't execute this on resume as the offline callback did
+	 * not get executed on suspend.
+	 */
+	if (cpuhp_tasks_frozen)
+		return 0;
+
+	/*
 	 * CPUID.06H.EAX[0] indicates whether the CPU has thermal
 	 * sensors. We check this bit only, all the early CPUs
 	 * without thermal sensors will be filtered out.
@@ -654,6 +661,13 @@ static int coretemp_cpu_offline(unsigned
 	struct temp_data *tdata;
 	int indx, target;
 
+	/*
+	 * Don't execute this on suspend as the device remove locks
+	 * up the machine.
+	 */
+	if (cpuhp_tasks_frozen)
+		return 0;
+
 	/* If the physical CPU device does not exist, just return */
 	if (!pdev)
 		return 0;