> From: Srivatsa S. Bhat [mailto:srivatsa.b...@linux.vnet.ibm.com] > On 10/16/2012 02:20 AM, Rafael J. Wysocki wrote: > > On Friday 12 of October 2012 09:09:42 Fenghua Yu wrote: > >> From: Fenghua Yu <fenghua...@intel.com> > >> > >> Because x86 BIOS requires CPU0 to resume from sleep, suspend or > hibernate can't > >> be executed if CPU0 is detected offline. To make suspend or > hibernate and > >> further resume succeed, CPU0 must be online. > >> > >> Signed-off-by: Fenghua Yu <fenghua...@intel.com> > >> --- > >> arch/x86/power/cpu.c | 44 > ++++++++++++++++++++++++++++++++++++++++++++ > >> 1 files changed, 44 insertions(+), 0 deletions(-) > >> > >> diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c > >> index 218cdb1..adde775 100644 > >> --- a/arch/x86/power/cpu.c > >> +++ b/arch/x86/power/cpu.c > >> @@ -237,3 +237,47 @@ void restore_processor_state(void) > >> #ifdef CONFIG_X86_32 > >> EXPORT_SYMBOL(restore_processor_state); > >> #endif > >> + > >> +/* > >> + * When bsp_check() is called in hibernate and suspend, cpu hotplug > >> + * is disabled already. So it's unnessary to handle race condition > between > >> + * cpumask query and cpu hotplug. > >> + */ > >> +static int bsp_check(void) > >> +{ > >> + if (cpumask_first(cpu_online_mask) != 0) { > >> + pr_warn("CPU0 is offline.\n"); > >> + return -ENODEV; > >> + } > >> + > >> + return 0; > >> +} > >> + > >> +static int bsp_pm_callback(struct notifier_block *nb, unsigned long > action, > >> + void *ptr) > >> +{ > >> + int ret = 0; > >> + > >> + switch (action) { > >> + case PM_SUSPEND_PREPARE: > >> + case PM_HIBERNATION_PREPARE: > >> + ret = bsp_check(); > >> + break; > >> + default: > >> + break; > >> + } > >> + return notifier_from_errno(ret); > >> +} > >> + > > > > I wonder if there's anything preventing CPU0 from becoming offline > after you've > > done this check and before user space is frozen? > > > > Hi Rafael, > > bsp_pm_callback runs as a low priority notifier callback, specifically > with lower > priority than the cpu_hotplug_pm_callback (as mentioned in the comment > below). > And cpu_hotplug_pm_callback disables regular CPU hotplug (till the > suspend/resume > sequence is complete).. So there is no chance for CPU0 to become > offline after that.
Bhat is right here. There is no functionality issue here. bsp_check() is protected by cpu_hotplug_disable which is set before bsp_pm_callback and cleared after it. There is no chance for CPU0 to be offline after that. Thanks. -Fenghua
