#include <linux/sysctl.h>
/*
- * Have a reasonable limit on the number of tasks checked:
+ * The number of tasks checked:
*/
-unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
+unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
+
+/*
+ * Limit number of tasks checked in a batch.
+ *
+ * This value controls the preemptibility of khungtaskd since preemption
+ * is disabled during the critical section. It also controls the size of
+ * the RCU grace period. So it needs to be upper-bound.
+ */
+#define HUNG_TASK_BATCHING 1024
/*
* Zero means infinite timeout - no checking done:
*/
unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
-static unsigned long __read_mostly hung_task_poll_jiffies;
unsigned long __read_mostly sysctl_hung_task_warnings = 10;
.notifier_call = hung_task_panic,
};
-/*
- * Returns seconds, approximately. We don't need nanosecond
- * resolution, and we don't need to waste time with a big divide when
- * 2^30ns == 1.074s.
- */
-static unsigned long get_timestamp(void)
-{
- int this_cpu = raw_smp_processor_id();
-
- return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
-}
-
-static void check_hung_task(struct task_struct *t, unsigned long now,
- unsigned long timeout)
+static void check_hung_task(struct task_struct *t, unsigned long timeout)
{
unsigned long switch_count = t->nvcsw + t->nivcsw;
- if (t->flags & PF_FROZEN)
+ /*
+ * Ensure the task is not frozen.
+ * Also, when a freshly created task is scheduled once, changes
+ * its state to TASK_UNINTERRUPTIBLE without having ever been
+ * switched out once, it musn't be checked.
+ */
+ if (unlikely(t->flags & PF_FROZEN || !switch_count))
return;
- if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
+ if (switch_count != t->last_switch_count) {
t->last_switch_count = switch_count;
- t->last_switch_timestamp = now;
return;
}
- if ((long)(now - t->last_switch_timestamp) < timeout)
- return;
if (!sysctl_hung_task_warnings)
return;
sysctl_hung_task_warnings--;
sched_show_task(t);
__debug_show_held_locks(t);
- t->last_switch_timestamp = now;
touch_nmi_watchdog();
if (sysctl_hung_task_panic)
}
/*
+ * To avoid extending the RCU grace period for an unbounded amount of time,
+ * periodically exit the critical section and enter a new one.
+ *
+ * For preemptible RCU it is sufficient to call rcu_read_unlock in order
+ * exit the grace period. For classic RCU, a reschedule is required.
+ */
+static void rcu_lock_break(struct task_struct *g, struct task_struct *t)
+{
+ get_task_struct(g);
+ get_task_struct(t);
+ rcu_read_unlock();
+ cond_resched();
+ rcu_read_lock();
+ put_task_struct(t);
+ put_task_struct(g);
+}
+
+/*
* Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
* a really long time (120 seconds). If that happens, print out
* a warning.
static void check_hung_uninterruptible_tasks(unsigned long timeout)
{
int max_count = sysctl_hung_task_check_count;
- unsigned long now = get_timestamp();
+ int batch_count = HUNG_TASK_BATCHING;
struct task_struct *g, *t;
/*
if (test_taint(TAINT_DIE) || did_panic)
return;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
do_each_thread(g, t) {
- if (!--max_count)
+ if (!max_count--)
goto unlock;
+ if (!--batch_count) {
+ batch_count = HUNG_TASK_BATCHING;
+ rcu_lock_break(g, t);
+ /* Exit if t or g was unhashed during refresh. */
+ if (t->state == TASK_DEAD || g->state == TASK_DEAD)
+ goto unlock;
+ }
/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
if (t->state == TASK_UNINTERRUPTIBLE)
- check_hung_task(t, now, timeout);
+ check_hung_task(t, timeout);
} while_each_thread(g, t);
unlock:
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
}
-static void update_poll_jiffies(void)
+static unsigned long timeout_jiffies(unsigned long timeout)
{
/* timeout of 0 will disable the watchdog */
- if (sysctl_hung_task_timeout_secs == 0)
- hung_task_poll_jiffies = MAX_SCHEDULE_TIMEOUT;
- else
- hung_task_poll_jiffies = sysctl_hung_task_timeout_secs * HZ / 2;
+ return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
}
/*
* Process updating of timeout sysctl
*/
int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
- struct file *filp, void __user *buffer,
+ void __user *buffer,
size_t *lenp, loff_t *ppos)
{
int ret;
- ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
+ ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
if (ret || !write)
goto out;
- update_poll_jiffies();
-
wake_up_process(watchdog_task);
out:
static int watchdog(void *dummy)
{
set_user_nice(current, 0);
- update_poll_jiffies();
for ( ; ; ) {
- unsigned long timeout;
+ unsigned long timeout = sysctl_hung_task_timeout_secs;
- while (schedule_timeout_interruptible(hung_task_poll_jiffies));
+ while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
+ timeout = sysctl_hung_task_timeout_secs;
- /*
- * Need to cache timeout here to avoid timeout being set
- * to 0 via sysctl while inside check_hung_*_tasks().
- */
- timeout = sysctl_hung_task_timeout_secs;
- if (timeout)
- check_hung_uninterruptible_tasks(timeout);
+ check_hung_uninterruptible_tasks(timeout);
}
return 0;
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff