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![Rafael J. Wysocki](/assets/img/avatar_default.png)
Currently, the freezer treats all tasks as freezable, except for the kernel threads that explicitly set the PF_NOFREEZE flag for themselves. This approach is problematic, since it requires every kernel thread to either set PF_NOFREEZE explicitly, or call try_to_freeze(), even if it doesn't care for the freezing of tasks at all. It seems better to only require the kernel threads that want to or need to be frozen to use some freezer-related code and to remove any freezer-related code from the other (nonfreezable) kernel threads, which is done in this patch. The patch causes all kernel threads to be nonfreezable by default (ie. to have PF_NOFREEZE set by default) and introduces the set_freezable() function that should be called by the freezable kernel threads in order to unset PF_NOFREEZE. It also makes all of the currently freezable kernel threads call set_freezable(), so it shouldn't cause any (intentional) change of behaviour to appear. Additionally, it updates documentation to describe the freezing of tasks more accurately. [akpm@linux-foundation.org: build fixes] Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> Acked-by: Nigel Cunningham <nigel@nigel.suspend2.net> Cc: Pavel Machek <pavel@ucw.cz> Cc: Oleg Nesterov <oleg@tv-sign.ru> Cc: Gautham R Shenoy <ego@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
197 lines
4.8 KiB
C
197 lines
4.8 KiB
C
/*
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* Detect Soft Lockups
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*
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* started by Ingo Molnar, Copyright (C) 2005, 2006 Red Hat, Inc.
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*
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* this code detects soft lockups: incidents in where on a CPU
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* the kernel does not reschedule for 10 seconds or more.
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*/
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#include <linux/mm.h>
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#include <linux/cpu.h>
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#include <linux/init.h>
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#include <linux/delay.h>
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#include <linux/freezer.h>
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#include <linux/kthread.h>
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#include <linux/notifier.h>
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#include <linux/module.h>
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static DEFINE_SPINLOCK(print_lock);
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static DEFINE_PER_CPU(unsigned long, touch_timestamp);
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static DEFINE_PER_CPU(unsigned long, print_timestamp);
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static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
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static int did_panic = 0;
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static int
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softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
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{
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did_panic = 1;
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return NOTIFY_DONE;
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}
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static struct notifier_block panic_block = {
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.notifier_call = softlock_panic,
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};
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/*
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* Returns seconds, approximately. We don't need nanosecond
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* resolution, and we don't need to waste time with a big divide when
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* 2^30ns == 1.074s.
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*/
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static unsigned long get_timestamp(void)
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{
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return sched_clock() >> 30; /* 2^30 ~= 10^9 */
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}
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void touch_softlockup_watchdog(void)
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{
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__raw_get_cpu_var(touch_timestamp) = get_timestamp();
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}
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EXPORT_SYMBOL(touch_softlockup_watchdog);
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void touch_all_softlockup_watchdogs(void)
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{
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int cpu;
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/* Cause each CPU to re-update its timestamp rather than complain */
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for_each_online_cpu(cpu)
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per_cpu(touch_timestamp, cpu) = 0;
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}
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EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
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/*
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* This callback runs from the timer interrupt, and checks
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* whether the watchdog thread has hung or not:
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*/
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void softlockup_tick(void)
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{
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int this_cpu = smp_processor_id();
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unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
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unsigned long print_timestamp;
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unsigned long now;
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if (touch_timestamp == 0) {
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touch_softlockup_watchdog();
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return;
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}
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print_timestamp = per_cpu(print_timestamp, this_cpu);
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/* report at most once a second */
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if (print_timestamp < (touch_timestamp + 1) ||
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did_panic ||
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!per_cpu(watchdog_task, this_cpu))
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return;
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/* do not print during early bootup: */
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if (unlikely(system_state != SYSTEM_RUNNING)) {
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touch_softlockup_watchdog();
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return;
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}
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now = get_timestamp();
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/* Wake up the high-prio watchdog task every second: */
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if (now > (touch_timestamp + 1))
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wake_up_process(per_cpu(watchdog_task, this_cpu));
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/* Warn about unreasonable 10+ seconds delays: */
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if (now > (touch_timestamp + 10)) {
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per_cpu(print_timestamp, this_cpu) = touch_timestamp;
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spin_lock(&print_lock);
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printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n",
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this_cpu);
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dump_stack();
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spin_unlock(&print_lock);
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}
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}
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/*
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* The watchdog thread - runs every second and touches the timestamp.
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*/
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static int watchdog(void * __bind_cpu)
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{
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struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
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sched_setscheduler(current, SCHED_FIFO, ¶m);
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/* initialize timestamp */
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touch_softlockup_watchdog();
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/*
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* Run briefly once per second to reset the softlockup timestamp.
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* If this gets delayed for more than 10 seconds then the
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* debug-printout triggers in softlockup_tick().
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*/
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while (!kthread_should_stop()) {
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set_current_state(TASK_INTERRUPTIBLE);
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touch_softlockup_watchdog();
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schedule();
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}
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return 0;
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}
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/*
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* Create/destroy watchdog threads as CPUs come and go:
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*/
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static int __cpuinit
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cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
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{
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int hotcpu = (unsigned long)hcpu;
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struct task_struct *p;
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switch (action) {
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case CPU_UP_PREPARE:
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case CPU_UP_PREPARE_FROZEN:
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BUG_ON(per_cpu(watchdog_task, hotcpu));
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p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
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if (IS_ERR(p)) {
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printk("watchdog for %i failed\n", hotcpu);
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return NOTIFY_BAD;
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}
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per_cpu(touch_timestamp, hotcpu) = 0;
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per_cpu(watchdog_task, hotcpu) = p;
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kthread_bind(p, hotcpu);
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break;
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case CPU_ONLINE:
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case CPU_ONLINE_FROZEN:
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wake_up_process(per_cpu(watchdog_task, hotcpu));
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break;
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#ifdef CONFIG_HOTPLUG_CPU
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case CPU_UP_CANCELED:
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case CPU_UP_CANCELED_FROZEN:
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if (!per_cpu(watchdog_task, hotcpu))
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break;
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/* Unbind so it can run. Fall thru. */
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kthread_bind(per_cpu(watchdog_task, hotcpu),
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any_online_cpu(cpu_online_map));
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case CPU_DEAD:
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case CPU_DEAD_FROZEN:
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p = per_cpu(watchdog_task, hotcpu);
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per_cpu(watchdog_task, hotcpu) = NULL;
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kthread_stop(p);
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break;
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#endif /* CONFIG_HOTPLUG_CPU */
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}
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return NOTIFY_OK;
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}
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static struct notifier_block __cpuinitdata cpu_nfb = {
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.notifier_call = cpu_callback
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};
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__init void spawn_softlockup_task(void)
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{
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void *cpu = (void *)(long)smp_processor_id();
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int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
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BUG_ON(err == NOTIFY_BAD);
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cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
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register_cpu_notifier(&cpu_nfb);
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atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
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}
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