From 79cfbdfa87e84992d509e6c1648a18e1d7e68c20 Mon Sep 17 00:00:00 2001 From: "Srivatsa S. Bhat" Date: Thu, 3 Nov 2011 00:59:25 +0100 Subject: PM / Sleep: Fix race between CPU hotplug and freezer The CPU hotplug notifications sent out by the _cpu_up() and _cpu_down() functions depend on the value of the 'tasks_frozen' argument passed to them (which indicates whether tasks have been frozen or not). (Examples for such CPU hotplug notifications: CPU_ONLINE, CPU_ONLINE_FROZEN, CPU_DEAD, CPU_DEAD_FROZEN). Thus, it is essential that while the callbacks for those notifications are running, the state of the system with respect to the tasks being frozen or not remains unchanged, *throughout that duration*. Hence there is a need for synchronizing the CPU hotplug code with the freezer subsystem. Since the freezer is involved only in the Suspend/Hibernate call paths, this patch hooks the CPU hotplug code to the suspend/hibernate notifiers PM_[SUSPEND|HIBERNATE]_PREPARE and PM_POST_[SUSPEND|HIBERNATE] to prevent the race between CPU hotplug and freezer, thus ensuring that CPU hotplug notifications will always be run with the state of the system really being what the notifications indicate, _throughout_ their execution time. Signed-off-by: Srivatsa S. Bhat Signed-off-by: Rafael J. Wysocki --- kernel/cpu.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 74 insertions(+) (limited to 'kernel') diff --git a/kernel/cpu.c b/kernel/cpu.c index 12b7458f23b1..aa39dd7a3846 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -15,6 +15,7 @@ #include #include #include +#include #ifdef CONFIG_SMP /* Serializes the updates to cpu_online_mask, cpu_present_mask */ @@ -476,6 +477,79 @@ static int alloc_frozen_cpus(void) return 0; } core_initcall(alloc_frozen_cpus); + +/* + * Prevent regular CPU hotplug from racing with the freezer, by disabling CPU + * hotplug when tasks are about to be frozen. Also, don't allow the freezer + * 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 gets completed. + */ +void cpu_hotplug_disable_before_freeze(void) +{ + cpu_maps_update_begin(); + cpu_hotplug_disabled = 1; + cpu_maps_update_done(); +} + + +/* + * When tasks have been thawed, re-enable regular CPU hotplug (which had been + * disabled while beginning to freeze tasks). + */ +void cpu_hotplug_enable_after_thaw(void) +{ + cpu_maps_update_begin(); + cpu_hotplug_disabled = 0; + cpu_maps_update_done(); +} + +/* + * When callbacks for CPU hotplug notifications are being executed, we must + * ensure that the state of the system with respect to the tasks being frozen + * or not, as reported by the notification, remains unchanged *throughout the + * duration* of the execution of the callbacks. + * Hence we need to prevent the freezer from racing with regular CPU hotplug. + * + * This synchronization is implemented by mutually excluding regular CPU + * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/ + * Hibernate notifications. + */ +static int +cpu_hotplug_pm_callback(struct notifier_block *nb, + unsigned long action, void *ptr) +{ + switch (action) { + + case PM_SUSPEND_PREPARE: + case PM_HIBERNATION_PREPARE: + cpu_hotplug_disable_before_freeze(); + break; + + case PM_POST_SUSPEND: + case PM_POST_HIBERNATION: + cpu_hotplug_enable_after_thaw(); + break; + + default: + return NOTIFY_DONE; + } + + return NOTIFY_OK; +} + + +int cpu_hotplug_pm_sync_init(void) +{ + pm_notifier(cpu_hotplug_pm_callback, 0); + return 0; +} +core_initcall(cpu_hotplug_pm_sync_init); + #endif /* CONFIG_PM_SLEEP_SMP */ /** -- cgit v1.2.3 From 6513fd6972f725291ee8ce62c7a39fb8a6c7391e Mon Sep 17 00:00:00 2001 From: Guennadi Liakhovetski Date: Thu, 3 Nov 2011 10:12:36 +0100 Subject: PM / QoS: Remove redundant check Remove an "if" check, that repeats an equivalent one 6 lines above. Signed-off-by: Guennadi Liakhovetski Signed-off-by: Rafael J. Wysocki --- kernel/power/qos.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/power/qos.c b/kernel/power/qos.c index 1c1797dd1d1d..5167d996cd02 100644 --- a/kernel/power/qos.c +++ b/kernel/power/qos.c @@ -386,8 +386,7 @@ static int pm_qos_power_open(struct inode *inode, struct file *filp) pm_qos_add_request(req, pm_qos_class, PM_QOS_DEFAULT_VALUE); filp->private_data = req; - if (filp->private_data) - return 0; + return 0; } return -EPERM; } -- cgit v1.2.3 From d6cc76856d353a3a9c43bead33210b9216dce332 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 4 Nov 2011 01:04:52 +0100 Subject: PM / Freezer: Revert 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK_KILLABLE tasks too" Commit 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK_KILLABLE tasks too" updated fake_signal_wake_up() used by freezer to wake up KILLABLE tasks. Sending unsolicited wakeups to tasks in killable sleep is dangerous as there are code paths which depend on tasks not waking up spuriously from KILLABLE sleep. For example. sys_read() or page can sleep in TASK_KILLABLE assuming that wait/down/whatever _killable can only fail if we can not return to the usermode. TASK_TRACED is another obvious example. The previous patch updated wait_event_freezekillable() such that it doesn't depend on the spurious wakeup. This patch reverts the offending commit. Note that the spurious KILLABLE wakeup had other implicit effects in KILLABLE sleeps in nfs and cifs and those will need further updates to regain freezekillable behavior. Signed-off-by: Tejun Heo Signed-off-by: Rafael J. Wysocki --- kernel/freezer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/freezer.c b/kernel/freezer.c index 66a594e8ad2f..7b01de98bb6a 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -67,7 +67,7 @@ static void fake_signal_wake_up(struct task_struct *p) unsigned long flags; spin_lock_irqsave(&p->sighand->siglock, flags); - signal_wake_up(p, 1); + signal_wake_up(p, 0); spin_unlock_irqrestore(&p->sighand->siglock, flags); } -- cgit v1.2.3