Re: perf hw in kexeced kernel broken in tip

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2010-12-08 at 09:01 -0500, Don Zickus wrote:
> Privately, I used the above wrapped with for_each_online_cpu(cpu) and it
> worked fine for me. 


Something like so then?

---
Subject: perf: Stop all counters on reboot
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Wed Dec 08 15:29:02 CET 2010

Use the reboot notifier to detach all running counters on reboot, this
solves a problem with kexec where the new kernel doesn't expect
running counters (rightly so).

It will however decrease the coverage of the NMI watchdog. Making a
kexec specific reboot notifier callback would be best, however that
would require touching all notifier callback handlers as they are not
properly structured to deal with new state.

As a compromise, place the perf reboot notifier at the very last
position in the list.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
Index: linux-2.6/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/kernel/perf_event.c
+++ linux-2.6/kernel/perf_event.c
@@ -21,6 +21,7 @@
 #include <linux/dcache.h>
 #include <linux/percpu.h>
 #include <linux/ptrace.h>
+#include <linux/reboot.h>
 #include <linux/vmstat.h>
 #include <linux/vmalloc.h>
 #include <linux/hardirq.h>
@@ -6329,7 +6330,7 @@ static void __cpuinit perf_event_init_cp
 	mutex_unlock(&swhash->hlist_mutex);
 }
 
-#ifdef CONFIG_HOTPLUG_CPU
+#if defined CONFIG_HOTPLUG_CPU || defined CONFIG_KEXEC
 static void perf_pmu_rotate_stop(struct pmu *pmu)
 {
 	struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
@@ -6383,6 +6384,26 @@ static void perf_event_exit_cpu(int cpu)
 static inline void perf_event_exit_cpu(int cpu) { }
 #endif
 
+static int
+perf_reboot(struct notifier_block *notifier, unsigned long val, void *v)
+{
+	int cpu;
+
+	for_each_online_cpu(cpu)
+		perf_event_exit_cpu(cpu);
+
+	return NOTIFY_OK;
+}
+
+/*
+ * Run the perf reboot notifier at the very last possible moment so that
+ * the generic watchdog code runs as long as possible.
+ */
+static struct notifier_block perf_reboot_notifier = {
+	.notifier_call = perf_reboot,
+	.priority = INT_MIN,
+};
+
 static int __cpuinit
 perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
 {
@@ -6418,6 +6439,7 @@ void __init perf_event_init(void)
 	perf_pmu_register(&perf_task_clock);
 	perf_tp_register();
 	perf_cpu_notifier(perf_cpu_notify);
+	register_reboot_notifier(&perf_reboot_notifier);
 
 	ret = init_hw_breakpoint();
 	WARN(ret, "hw_breakpoint initialization failed with: %d", ret);