From: Ville Syrjälä ville.syrjala@linux.intel.com
Since 4.20-rc1 my PIC machines no longer reboot/shutdown. I bisected this down to commit 45975c7d21a1 ("rcu: Define RCU-sched API in terms of RCU for Tree RCU PREEMPT builds").
I traced the hang into -> cpufreq_suspend() -> cpufreq_stop_governor() -> cpufreq_dbs_governor_stop() -> gov_clear_update_util() -> synchronize_sched() -> synchronize_rcu()
Only PREEMPT=y is affected for obvious reasons. The problem is limited to PIC machines since they mask off interrupts in i8259A_shutdown() (syscore_ops.shutdown() registered from device_initcall()).
I reported this long ago but no better fix has surfaced, hence sending out my initial workaround which I've been carrying around ever since. I just move cpufreq_core_init() to late_initcall() so the syscore_ops get registered in the oppsite order and thus the .shutdown() hooks get executed in the opposite order as well. Not 100% convinced this is safe (especially moving the cpufreq_global_kobject creation to late_initcall()) but I've not had any problems with it at least.
Here's the resulting change in initcall_debug: + PM: Calling cpufreq_suspend+0x0/0x100 PM: Calling mce_syscore_shutdown+0x0/0x10 PM: Calling i8259A_shutdown+0x0/0x10 - PM: Calling cpufreq_suspend+0x0/0x100 + reboot: Restarting system + reboot: machine restart
Cc: stable@vger.kernel.org Cc: Paul E. McKenney paulmck@linux.vnet.ibm.com Cc: Andi Kleen ak@linux.intel.com Cc: "Rafael J. Wysocki" rjw@rjwysocki.net Cc: Viresh Kumar viresh.kumar@linaro.org Cc: linux-pm@vger.kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@redhat.com Cc: Borislav Petkov bp@alien8.de Cc: "H. Peter Anvin" hpa@zytor.com Fixes: 45975c7d21a1 ("rcu: Define RCU-sched API in terms of RCU for Tree RCU PREEMPT builds") Signed-off-by: Ville Syrjälä ville.syrjala@linux.intel.com --- drivers/cpufreq/cpufreq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index c52d6fa32aac..6a8fb9b08e33 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -2761,4 +2761,4 @@ static int __init cpufreq_core_init(void) return 0; } module_param(off, int, 0444); -core_initcall(cpufreq_core_init); +late_initcall(cpufreq_core_init);