Hi,
On Thursday, October 27, 2011, Srivatsa S. Bhat wrote:
> Prevent CPU hotplug and the freezer from racing with each other, to ensure
> that during the *entire duration* for which the callbacks for CPU hotplug
> notifications such as CPU_ONLINE[_FROZEN], CPU_DEAD[_FROZEN] etc are being
> executed, the state of the system (with respect to the tasks being frozen
> or not) remains constant.
>
> This patches hooks the CPU hotplug infrastructure onto the freezer
> notifications (PM_FREEZE_PREPARE and PM_POST_THAW) and thus synchronizes
> with the freezer.
>
> Specifically,
>
> * Upon the PM_FREEZE_PREPARE notification, the CPU hotplug callback disables
> future (regular) CPU hotplugging and also ensures that any currently running
> CPU hotplug operation is completed before allowing the freezer to continue
> any further.
>
> * Upon the PM_POST_THAW notification, the CPU hotplug callback re-enables
> regular CPU hotplug.
>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
> ---
>
> kernel/cpu.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 76 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 12b7458..61985ce 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -15,6 +15,7 @@
> #include <linux/stop_machine.h>
> #include <linux/mutex.h>
> #include <linux/gfp.h>
> +#include <linux/suspend.h>
>
> #ifdef CONFIG_SMP
> /* Serializes the updates to cpu_online_mask, cpu_present_mask */
> @@ -478,6 +479,81 @@ static int alloc_frozen_cpus(void)
> core_initcall(alloc_frozen_cpus);
> #endif /* CONFIG_PM_SLEEP_SMP */
>
> +
> +#ifdef CONFIG_FREEZER
> +
> +/*
> + * Avoid CPU hotplug racing with the freezer subsystem, by disabling CPU
> + * hotplug when tasks are about to be frozen.
> + *
> + * Also, don't allow the freezer subsystem to continue until any currently
> + * running CPU hotplug operation gets completed.
> + * To modify the 'cpu_hotplug_disabled' flag, we need to acquire the
> + * 'cpu_add_remove_lock'. And this same lock is also taken by the regular
> + * CPU hotplug path and released only after it is complete. Thus, we
> + * (and hence the freezer) will block here until any currently running CPU
> + * hotplug operation is completed.
> + */
> +static void cpu_hotplug_freezer_block_begin(void)
> +{
> + cpu_maps_update_begin();
> + cpu_hotplug_disabled = 1;
> + cpu_maps_update_done();
> +}
> +
> +
> +/*
> + * When thawing of tasks is complete, re-enable CPU hotplug (which had been
> + * disabled while beginning to freeze tasks).
> + */
> +static void cpu_hotplug_freezer_block_done(void)
> +{
> + cpu_maps_update_begin();
> + cpu_hotplug_disabled = 0;
> + cpu_maps_update_done();
> +}
> +
I wonder if the new PM notifier events are really necessary?
Why don't you just call cpu_hotplug_freezer_block_begin() (perhaps
with a better name?) directly from freeze_processes()? And analogously
for cpu_hotplug_freezer_block_done() and thaw_processes()?
Rafael
> +
> +/*
> + * Avoid CPU hotplug and the freezer subsystem from racing with each other,
> + * so that when CPU hotplug notifications are being sent (i.e., the
> + * registered callbacks being executed), the state of the system reported
> + * by the notifier (with respect to the tasks being frozen or not) is
> + * consistent with the actual state of the system, *throughout the duration*
> + * during which the CPU hotplug notifications are active.
> + */
> +static int
> +cpu_hotplug_freezer_callback(struct notifier_block *nb,
> + unsigned long action, void *ptr)
> +{
> + switch (action) {
> +
> + case PM_FREEZE_PREPARE:
> + cpu_hotplug_freezer_block_begin();
> + break;
> +
> + case PM_POST_THAW:
> + cpu_hotplug_freezer_block_done();
> + break;
> +
> + default:
> + return NOTIFY_DONE;
> + }
> +
> + return NOTIFY_OK;
> +}
> +
> +
> +int cpu_hotplug_freezer_sync_init(void)
> +{
> + pm_notifier(cpu_hotplug_freezer_callback, 0);
> + return 0;
> +}
> +core_initcall(cpu_hotplug_freezer_sync_init);
> +
> +#endif /* CONFIG_FREEZER */
> +
> +
> /**
> * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
> * @cpu: cpu that just started
>
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-doc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
