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Once kthread printing is available, console printing will no longer occur in the context of the printk caller. However, there are some special contexts where it is desirable for the printk caller to directly print out kernel messages. Using pr_flush() to wait for threaded printers is only possible if the caller is in a sleepable context and the kthreads are active. That is not always the case. Introduce printk_prefer_direct_enter() and printk_prefer_direct_exit() functions to explicitly (and globally) activate/deactivate preferred direct console printing. The term "direct console printing" refers to printing to all enabled consoles from the context of the printk caller. The term "prefer" is used because this type of printing is only best effort. If the console is currently locked or other printers are already actively printing, the printk caller will need to rely on the other contexts to handle the printing. This preferred direct printing is how all printing has been handled until now (unless it was explicitly deferred). When kthread printing is introduced, there may be some unanticipated problems due to kthreads being unable to flush important messages. In order to minimize such risks, preferred direct printing is activated for the primary important messages when the system experiences general types of major errors. These are: - emergency reboot/shutdown - cpu and rcu stalls - hard and soft lockups - hung tasks - warn - sysrq Note that since kthread printing does not yet exist, no behavior changes result from this commit. This is only implementing the counter and marking the various places where preferred direct printing is active. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Acked-by: Paul E. McKenney <paulmck@kernel.org> # for RCU Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20220421212250.565456-13-john.ogness@linutronix.de
401 lines
9.6 KiB
C
401 lines
9.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Detect Hung Task
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*
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* kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
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*
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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/nmi.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/lockdep.h>
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#include <linux/export.h>
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#include <linux/panic_notifier.h>
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#include <linux/sysctl.h>
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#include <linux/suspend.h>
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#include <linux/utsname.h>
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#include <linux/sched/signal.h>
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#include <linux/sched/debug.h>
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#include <linux/sched/sysctl.h>
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#include <trace/events/sched.h>
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/*
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* The number of tasks checked:
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*/
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int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
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/*
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* Limit number of tasks checked in a batch.
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*
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* This value controls the preemptibility of khungtaskd since preemption
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* is disabled during the critical section. It also controls the size of
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* the RCU grace period. So it needs to be upper-bound.
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*/
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#define HUNG_TASK_LOCK_BREAK (HZ / 10)
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/*
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* Zero means infinite timeout - no checking done:
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*/
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unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
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/*
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* Zero (default value) means use sysctl_hung_task_timeout_secs:
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*/
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unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
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int __read_mostly sysctl_hung_task_warnings = 10;
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static int __read_mostly did_panic;
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static bool hung_task_show_lock;
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static bool hung_task_call_panic;
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static bool hung_task_show_all_bt;
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static struct task_struct *watchdog_task;
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#ifdef CONFIG_SMP
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/*
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* Should we dump all CPUs backtraces in a hung task event?
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* Defaults to 0, can be changed via sysctl.
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*/
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static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
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#else
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#define sysctl_hung_task_all_cpu_backtrace 0
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#endif /* CONFIG_SMP */
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/*
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* Should we panic (and reboot, if panic_timeout= is set) when a
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* hung task is detected:
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*/
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unsigned int __read_mostly sysctl_hung_task_panic =
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CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
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static int
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hung_task_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 = hung_task_panic,
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};
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static void check_hung_task(struct task_struct *t, unsigned long timeout)
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{
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unsigned long switch_count = t->nvcsw + t->nivcsw;
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/*
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* Ensure the task is not frozen.
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* Also, skip vfork and any other user process that freezer should skip.
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*/
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if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
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return;
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/*
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* When a freshly created task is scheduled once, changes its state to
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* TASK_UNINTERRUPTIBLE without having ever been switched out once, it
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* musn't be checked.
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*/
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if (unlikely(!switch_count))
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return;
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if (switch_count != t->last_switch_count) {
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t->last_switch_count = switch_count;
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t->last_switch_time = jiffies;
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return;
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}
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if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
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return;
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trace_sched_process_hang(t);
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if (sysctl_hung_task_panic) {
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console_verbose();
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hung_task_show_lock = true;
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hung_task_call_panic = true;
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}
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/*
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* Ok, the task did not get scheduled for more than 2 minutes,
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* complain:
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*/
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if (sysctl_hung_task_warnings) {
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printk_prefer_direct_enter();
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if (sysctl_hung_task_warnings > 0)
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sysctl_hung_task_warnings--;
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pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
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t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
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pr_err(" %s %s %.*s\n",
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print_tainted(), init_utsname()->release,
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(int)strcspn(init_utsname()->version, " "),
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init_utsname()->version);
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pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
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" disables this message.\n");
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sched_show_task(t);
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hung_task_show_lock = true;
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if (sysctl_hung_task_all_cpu_backtrace)
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hung_task_show_all_bt = true;
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printk_prefer_direct_exit();
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}
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touch_nmi_watchdog();
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}
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/*
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* To avoid extending the RCU grace period for an unbounded amount of time,
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* periodically exit the critical section and enter a new one.
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*
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* For preemptible RCU it is sufficient to call rcu_read_unlock in order
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* to exit the grace period. For classic RCU, a reschedule is required.
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*/
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static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
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{
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bool can_cont;
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get_task_struct(g);
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get_task_struct(t);
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rcu_read_unlock();
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cond_resched();
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rcu_read_lock();
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can_cont = pid_alive(g) && pid_alive(t);
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put_task_struct(t);
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put_task_struct(g);
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return can_cont;
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}
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/*
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* Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
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* a really long time (120 seconds). If that happens, print out
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* a warning.
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*/
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static void check_hung_uninterruptible_tasks(unsigned long timeout)
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{
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int max_count = sysctl_hung_task_check_count;
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unsigned long last_break = jiffies;
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struct task_struct *g, *t;
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/*
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* If the system crashed already then all bets are off,
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* do not report extra hung tasks:
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*/
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if (test_taint(TAINT_DIE) || did_panic)
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return;
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hung_task_show_lock = false;
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rcu_read_lock();
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for_each_process_thread(g, t) {
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if (!max_count--)
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goto unlock;
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if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
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if (!rcu_lock_break(g, t))
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goto unlock;
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last_break = jiffies;
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}
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/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
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if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE)
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check_hung_task(t, timeout);
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}
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unlock:
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rcu_read_unlock();
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if (hung_task_show_lock) {
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printk_prefer_direct_enter();
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debug_show_all_locks();
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printk_prefer_direct_exit();
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}
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if (hung_task_show_all_bt) {
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hung_task_show_all_bt = false;
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printk_prefer_direct_enter();
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trigger_all_cpu_backtrace();
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printk_prefer_direct_exit();
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}
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if (hung_task_call_panic)
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panic("hung_task: blocked tasks");
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}
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static long hung_timeout_jiffies(unsigned long last_checked,
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unsigned long timeout)
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{
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/* timeout of 0 will disable the watchdog */
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return timeout ? last_checked - jiffies + timeout * HZ :
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MAX_SCHEDULE_TIMEOUT;
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}
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#ifdef CONFIG_SYSCTL
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/*
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* Process updating of timeout sysctl
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*/
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static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
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void __user *buffer,
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size_t *lenp, loff_t *ppos)
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{
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int ret;
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ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
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if (ret || !write)
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goto out;
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wake_up_process(watchdog_task);
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out:
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return ret;
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}
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/*
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* This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
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* and hung_task_check_interval_secs
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*/
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static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
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static struct ctl_table hung_task_sysctls[] = {
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#ifdef CONFIG_SMP
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{
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.procname = "hung_task_all_cpu_backtrace",
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.data = &sysctl_hung_task_all_cpu_backtrace,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = proc_dointvec_minmax,
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.extra1 = SYSCTL_ZERO,
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.extra2 = SYSCTL_ONE,
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},
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#endif /* CONFIG_SMP */
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{
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.procname = "hung_task_panic",
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.data = &sysctl_hung_task_panic,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = proc_dointvec_minmax,
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.extra1 = SYSCTL_ZERO,
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.extra2 = SYSCTL_ONE,
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},
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{
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.procname = "hung_task_check_count",
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.data = &sysctl_hung_task_check_count,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = proc_dointvec_minmax,
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.extra1 = SYSCTL_ZERO,
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},
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{
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.procname = "hung_task_timeout_secs",
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.data = &sysctl_hung_task_timeout_secs,
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.maxlen = sizeof(unsigned long),
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.mode = 0644,
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.proc_handler = proc_dohung_task_timeout_secs,
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.extra2 = (void *)&hung_task_timeout_max,
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},
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{
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.procname = "hung_task_check_interval_secs",
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.data = &sysctl_hung_task_check_interval_secs,
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.maxlen = sizeof(unsigned long),
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.mode = 0644,
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.proc_handler = proc_dohung_task_timeout_secs,
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.extra2 = (void *)&hung_task_timeout_max,
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},
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{
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.procname = "hung_task_warnings",
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.data = &sysctl_hung_task_warnings,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = proc_dointvec_minmax,
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.extra1 = SYSCTL_NEG_ONE,
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},
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{}
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};
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static void __init hung_task_sysctl_init(void)
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{
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register_sysctl_init("kernel", hung_task_sysctls);
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}
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#else
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#define hung_task_sysctl_init() do { } while (0)
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#endif /* CONFIG_SYSCTL */
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static atomic_t reset_hung_task = ATOMIC_INIT(0);
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void reset_hung_task_detector(void)
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{
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atomic_set(&reset_hung_task, 1);
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}
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EXPORT_SYMBOL_GPL(reset_hung_task_detector);
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static bool hung_detector_suspended;
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static int hungtask_pm_notify(struct notifier_block *self,
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unsigned long action, void *hcpu)
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{
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switch (action) {
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case PM_SUSPEND_PREPARE:
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case PM_HIBERNATION_PREPARE:
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case PM_RESTORE_PREPARE:
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hung_detector_suspended = true;
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break;
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case PM_POST_SUSPEND:
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case PM_POST_HIBERNATION:
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case PM_POST_RESTORE:
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hung_detector_suspended = false;
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break;
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default:
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break;
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}
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return NOTIFY_OK;
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}
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/*
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* kthread which checks for tasks stuck in D state
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*/
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static int watchdog(void *dummy)
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{
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unsigned long hung_last_checked = jiffies;
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set_user_nice(current, 0);
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for ( ; ; ) {
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unsigned long timeout = sysctl_hung_task_timeout_secs;
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unsigned long interval = sysctl_hung_task_check_interval_secs;
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long t;
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if (interval == 0)
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interval = timeout;
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interval = min_t(unsigned long, interval, timeout);
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t = hung_timeout_jiffies(hung_last_checked, interval);
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if (t <= 0) {
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if (!atomic_xchg(&reset_hung_task, 0) &&
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!hung_detector_suspended)
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check_hung_uninterruptible_tasks(timeout);
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hung_last_checked = jiffies;
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continue;
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}
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schedule_timeout_interruptible(t);
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}
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return 0;
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}
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static int __init hung_task_init(void)
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{
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atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
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/* Disable hung task detector on suspend */
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pm_notifier(hungtask_pm_notify, 0);
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watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
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hung_task_sysctl_init();
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return 0;
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}
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subsys_initcall(hung_task_init);
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