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https://github.com/edk2-porting/linux-next.git
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780cbcf287
When I was running my testcase which may block hundreds of threads on fs
locks, I got lockup due to output from debug_show_all_locks() added by
commit b2d4c2edb2
("locking/hung_task: Show all locks").
For example, if 1000 threads were blocked in TASK_UNINTERRUPTIBLE state
and 500 out of 1000 threads hold some lock, debug_show_all_locks() from
for_each_process_thread() loop will report locks held by 500 threads for
1000 times. This is a too much noise.
In order to make sure rcu_lock_break() is called frequently, we should
avoid calling debug_show_all_locks() from for_each_process_thread() loop
because debug_show_all_locks() effectively calls for_each_process_thread()
loop. Let's defer calling debug_show_all_locks() till before panic() or
leaving for_each_process_thread() loop.
Link: http://lkml.kernel.org/r/1489296834-60436-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
267 lines
6.2 KiB
C
267 lines
6.2 KiB
C
/*
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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/sysctl.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 <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_BATCHING 1024
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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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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 struct task_struct *watchdog_task;
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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 __init hung_task_panic_setup(char *str)
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{
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int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
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if (rc)
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return rc;
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return 1;
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}
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__setup("hung_task_panic=", hung_task_panic_setup);
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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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return;
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}
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trace_sched_process_hang(t);
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if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
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return;
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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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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, timeout);
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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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}
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touch_nmi_watchdog();
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if (sysctl_hung_task_panic) {
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if (hung_task_show_lock)
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debug_show_all_locks();
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trigger_all_cpu_backtrace();
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panic("hung_task: blocked tasks");
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}
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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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int batch_count = HUNG_TASK_BATCHING;
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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 (!--batch_count) {
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batch_count = HUNG_TASK_BATCHING;
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if (!rcu_lock_break(g, t))
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goto unlock;
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}
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/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
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if (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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debug_show_all_locks();
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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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/*
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* Process updating of timeout sysctl
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*/
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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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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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/*
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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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long t = hung_timeout_jiffies(hung_last_checked, timeout);
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if (t <= 0) {
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if (!atomic_xchg(&reset_hung_task, 0))
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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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watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
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return 0;
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}
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subsys_initcall(hung_task_init);
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