From e162b39a368f0401e41b558f430c354d12a85b37 Mon Sep 17 00:00:00 2001
From: Mandeep Singh Baines <msb@google.com>
Date: Thu, 15 Jan 2009 11:08:40 -0800
Subject: softlockup: decouple hung tasks check from softlockup detection
Decoupling allows:
* hung tasks check to happen at very low priority
* hung tasks check and softlockup to be enabled/disabled independently
at compile and/or run-time
* individual panic settings to be enabled disabled independently
at compile and/or run-time
* softlockup threshold to be reduced without increasing hung tasks
poll frequency (hung task check is expensive relative to softlock watchdog)
* hung task check to be zero over-head when disabled at run-time
Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/hung_task.c | 198 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 198 insertions(+)
create mode 100644 kernel/hung_task.c
(limited to 'kernel/hung_task.c')
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
new file mode 100644
index 00000000000..ba5a77cad3b
--- /dev/null
+++ b/kernel/hung_task.c
@@ -0,0 +1,198 @@
+/*
+ * Detect Hung Task
+ *
+ * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
+ *
+ */
+
+#include <linux/mm.h>
+#include <linux/cpu.h>
+#include <linux/nmi.h>
+#include <linux/init.h>
+#include <linux/delay.h>
+#include <linux/freezer.h>
+#include <linux/kthread.h>
+#include <linux/lockdep.h>
+#include <linux/module.h>
+#include <linux/sysctl.h>
+
+/*
+ * Have a reasonable limit on the number of tasks checked:
+ */
+unsigned long __read_mostly sysctl_hung_task_check_count = 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;
+
+static int __read_mostly did_panic;
+
+static struct task_struct *watchdog_task;
+
+/*
+ * Should we panic (and reboot, if panic_timeout= is set) when a
+ * hung task is detected:
+ */
+unsigned int __read_mostly sysctl_hung_task_panic =
+ CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
+
+static int __init hung_task_panic_setup(char *str)
+{
+ sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
+
+ return 1;
+}
+__setup("hung_task_panic=", hung_task_panic_setup);
+
+static int
+hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
+{
+ did_panic = 1;
+
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block panic_block = {
+ .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 switch_count = t->nvcsw + t->nivcsw;
+
+ if (t->flags & PF_FROZEN)
+ return;
+
+ if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
+ t->last_switch_count = switch_count;
+ t->last_switch_timestamp = now;
+ return;
+ }
+ if ((long)(now - t->last_switch_timestamp) <
+ sysctl_hung_task_timeout_secs)
+ return;
+ if (!sysctl_hung_task_warnings)
+ return;
+ sysctl_hung_task_warnings--;
+
+ /*
+ * Ok, the task did not get scheduled for more than 2 minutes,
+ * complain:
+ */
+ printk(KERN_ERR "INFO: task %s:%d blocked for more than "
+ "%ld seconds.\n", t->comm, t->pid,
+ sysctl_hung_task_timeout_secs);
+ printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
+ " disables this message.\n");
+ sched_show_task(t);
+ __debug_show_held_locks(t);
+
+ t->last_switch_timestamp = now;
+ touch_nmi_watchdog();
+
+ if (sysctl_hung_task_panic)
+ panic("hung_task: blocked tasks");
+}
+
+/*
+ * 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(void)
+{
+ int max_count = sysctl_hung_task_check_count;
+ unsigned long now = get_timestamp();
+ struct task_struct *g, *t;
+
+ /*
+ * If the system crashed already then all bets are off,
+ * do not report extra hung tasks:
+ */
+ if (test_taint(TAINT_DIE) || did_panic)
+ return;
+
+ read_lock(&tasklist_lock);
+ do_each_thread(g, t) {
+ if (!--max_count)
+ goto unlock;
+ /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
+ if (t->state == TASK_UNINTERRUPTIBLE)
+ check_hung_task(t, now);
+ } while_each_thread(g, t);
+ unlock:
+ read_unlock(&tasklist_lock);
+}
+
+static void update_poll_jiffies(void)
+{
+ /* 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;
+}
+
+/*
+ * Process updating of timeout sysctl
+ */
+int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
+ struct file *filp, void __user *buffer,
+ size_t *lenp, loff_t *ppos)
+{
+ int ret;
+
+ ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
+
+ if (ret || !write)
+ goto out;
+
+ update_poll_jiffies();
+
+ wake_up_process(watchdog_task);
+
+ out:
+ return ret;
+}
+
+/*
+ * kthread which checks for tasks stuck in D state
+ */
+static int watchdog(void *dummy)
+{
+ set_user_nice(current, 0);
+ update_poll_jiffies();
+
+ for ( ; ; ) {
+ while (schedule_timeout_interruptible(hung_task_poll_jiffies));
+ check_hung_uninterruptible_tasks();
+ }
+
+ return 0;
+}
+
+static int __init hung_task_init(void)
+{
+ atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
+ watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
+
+ return 0;
+}
+
+module_init(hung_task_init);
--
cgit v1.2.3-70-g09d2
From 603a148f434742fff08273207ffa44176cad13a1 Mon Sep 17 00:00:00 2001
From: Mandeep Singh Baines <msb@google.com>
Date: Sat, 17 Jan 2009 10:31:48 -0800
Subject: softlockup: fix potential race in hung_task when resetting timeout
Impact: fix potential false panic
A potential race exists if sysctl_hung_task_timeout_secs is reset to 0
while inside check_hung_uniterruptible_tasks(). If check_task() is
entered, a comparison with 0 will result in a false hung_task being
detected.
If sysctl_hung_task_panic is set, the system will panic.
Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/hung_task.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)
(limited to 'kernel/hung_task.c')
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index ba5a77cad3b..ba8ccd43296 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -72,7 +72,8 @@ static unsigned long get_timestamp(void)
return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
}
-static void check_hung_task(struct task_struct *t, unsigned long now)
+static void check_hung_task(struct task_struct *t, unsigned long now,
+ unsigned long timeout)
{
unsigned long switch_count = t->nvcsw + t->nivcsw;
@@ -84,8 +85,7 @@ static void check_hung_task(struct task_struct *t, unsigned long now)
t->last_switch_timestamp = now;
return;
}
- if ((long)(now - t->last_switch_timestamp) <
- sysctl_hung_task_timeout_secs)
+ if ((long)(now - t->last_switch_timestamp) < timeout)
return;
if (!sysctl_hung_task_warnings)
return;
@@ -96,8 +96,7 @@ static void check_hung_task(struct task_struct *t, unsigned long now)
* complain:
*/
printk(KERN_ERR "INFO: task %s:%d blocked for more than "
- "%ld seconds.\n", t->comm, t->pid,
- sysctl_hung_task_timeout_secs);
+ "%ld seconds.\n", t->comm, t->pid, timeout);
printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
" disables this message.\n");
sched_show_task(t);
@@ -115,7 +114,7 @@ static void check_hung_task(struct task_struct *t, unsigned long now)
* a really long time (120 seconds). If that happens, print out
* a warning.
*/
-static void check_hung_uninterruptible_tasks(void)
+static void check_hung_uninterruptible_tasks(unsigned long timeout)
{
int max_count = sysctl_hung_task_check_count;
unsigned long now = get_timestamp();
@@ -134,7 +133,7 @@ static void check_hung_uninterruptible_tasks(void)
goto unlock;
/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
if (t->state == TASK_UNINTERRUPTIBLE)
- check_hung_task(t, now);
+ check_hung_task(t, now, timeout);
} while_each_thread(g, t);
unlock:
read_unlock(&tasklist_lock);
@@ -180,8 +179,17 @@ static int watchdog(void *dummy)
update_poll_jiffies();
for ( ; ; ) {
+ unsigned long timeout;
+
while (schedule_timeout_interruptible(hung_task_poll_jiffies));
- check_hung_uninterruptible_tasks();
+
+ /*
+ * 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);
}
return 0;
--
cgit v1.2.3-70-g09d2
From ce9dbe244bf2063c41792e40dae7745957b118e0 Mon Sep 17 00:00:00 2001
From: Mandeep Singh Baines <msb@google.com>
Date: Wed, 4 Feb 2009 20:35:48 -0800
Subject: softlockup: check all tasks in hung_task
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Impact: extend the scope of hung-task checks
Changed the default value of hung_task_check_count to PID_MAX_LIMIT.
hung_task_batch_count added to put an upper bound on the critical
section. Every hung_task_batch_count checks, the rcu lock is never
held for a too long time.
Keeping the critical section small minimizes time preemption is disabled
and keeps rcu grace periods small.
To prevent following a stale pointer, get_task_struct is called on g and t.
To verify that g and t have not been unhashed while outside the critical
section, the task states are checked.
The design was proposed by Frédéric Weisbecker.
Signed-off-by: Mandeep Singh Baines <msb@google.com>
Suggested-by: Frédéric Weisbecker <fweisbec@gmail.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/hung_task.c | 39 +++++++++++++++++++++++++++++++++++++--
1 file changed, 37 insertions(+), 2 deletions(-)
(limited to 'kernel/hung_task.c')
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index ba8ccd43296..481ca8b5c2b 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -17,9 +17,18 @@
#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:
@@ -109,6 +118,24 @@ static void check_hung_task(struct task_struct *t, unsigned long now,
panic("hung_task: blocked tasks");
}
+/*
+ * 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
@@ -117,6 +144,7 @@ static void check_hung_task(struct task_struct *t, unsigned long now,
static void check_hung_uninterruptible_tasks(unsigned long timeout)
{
int max_count = sysctl_hung_task_check_count;
+ int batch_count = HUNG_TASK_BATCHING;
unsigned long now = get_timestamp();
struct task_struct *g, *t;
@@ -131,6 +159,13 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
do_each_thread(g, t) {
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);
--
cgit v1.2.3-70-g09d2
From 94be52dc075a32af4aa73d7e10f68734d62d6af2 Mon Sep 17 00:00:00 2001
From: Mandeep Singh Baines <msb@google.com>
Date: Thu, 5 Feb 2009 09:56:08 -0800
Subject: softlockup: convert read_lock in hung_task to rcu_read_lock
Since the tasklist is protected by rcu list operations, it is safe
to convert the read_lock()s to rcu_read_lock().
Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/hung_task.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
(limited to 'kernel/hung_task.c')
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 481ca8b5c2b..3951a80e7cb 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -155,7 +155,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
if (test_taint(TAINT_DIE) || did_panic)
return;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
do_each_thread(g, t) {
if (!--max_count)
goto unlock;
@@ -171,7 +171,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
check_hung_task(t, now, timeout);
} while_each_thread(g, t);
unlock:
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
}
static void update_poll_jiffies(void)
--
cgit v1.2.3-70-g09d2
From 17406b82d621930cca8ccc1272cdac9a7dae8e40 Mon Sep 17 00:00:00 2001
From: Mandeep Singh Baines <msb@google.com>
Date: Fri, 6 Feb 2009 15:37:47 -0800
Subject: softlockup: remove timestamp checking from hung_task
Impact: saves sizeof(long) bytes per task_struct
By guaranteeing that sysctl_hung_task_timeout_secs have elapsed between
tasklist scans we can avoid using timestamps.
Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
include/linux/sched.h | 1 -
kernel/fork.c | 8 +++-----
kernel/hung_task.c | 48 +++++++++---------------------------------------
3 files changed, 12 insertions(+), 45 deletions(-)
(limited to 'kernel/hung_task.c')
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2a2811c6239..e0d723fea9f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1241,7 +1241,6 @@ struct task_struct {
#endif
#ifdef CONFIG_DETECT_HUNG_TASK
/* hung task detection */
- unsigned long last_switch_timestamp;
unsigned long last_switch_count;
#endif
/* CPU-specific state of this task */
diff --git a/kernel/fork.c b/kernel/fork.c
index fb944428283..bf582f75014 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -639,6 +639,9 @@ static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
tsk->min_flt = tsk->maj_flt = 0;
tsk->nvcsw = tsk->nivcsw = 0;
+#ifdef CONFIG_DETECT_HUNG_TASK
+ tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
+#endif
tsk->mm = NULL;
tsk->active_mm = NULL;
@@ -1041,11 +1044,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->default_timer_slack_ns = current->timer_slack_ns;
-#ifdef CONFIG_DETECT_HUNG_TASK
- p->last_switch_count = 0;
- p->last_switch_timestamp = 0;
-#endif
-
task_io_accounting_init(&p->ioac);
acct_clear_integrals(p);
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 3951a80e7cb..0c924de58cb 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -34,7 +34,6 @@ unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
* 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;
@@ -69,33 +68,17 @@ static struct notifier_block panic_block = {
.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)
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--;
@@ -111,7 +94,6 @@ static void check_hung_task(struct task_struct *t, unsigned long now,
sched_show_task(t);
__debug_show_held_locks(t);
- t->last_switch_timestamp = now;
touch_nmi_watchdog();
if (sysctl_hung_task_panic)
@@ -145,7 +127,6 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
{
int max_count = sysctl_hung_task_check_count;
int batch_count = HUNG_TASK_BATCHING;
- unsigned long now = get_timestamp();
struct task_struct *g, *t;
/*
@@ -168,19 +149,16 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
}
/* 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:
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;
}
/*
@@ -197,8 +175,6 @@ int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
if (ret || !write)
goto out;
- update_poll_jiffies();
-
wake_up_process(watchdog_task);
out:
@@ -211,20 +187,14 @@ int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
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;
--
cgit v1.2.3-70-g09d2
From cf2592f59c0e8ed4308adbdb2e0a88655379d579 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <fweisbec@gmail.com>
Date: Tue, 10 Feb 2009 16:52:37 +0100
Subject: softlockup: ensure the task has been switched out once
When we check if a task has been switched out since the last scan, we might
have a race condition on the following scenario:
- the task is freshly created and scheduled
- it puts its state to TASK_UNINTERRUPTIBLE and is not yet switched out
- check_hung_task() scans this task and will report a false positive because
t->nvcsw + t->nivcsw == t->last_switch_count == 0
Add a check for such cases.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/hung_task.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
(limited to 'kernel/hung_task.c')
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 0c924de58cb..022a4927b78 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -72,7 +72,13 @@ 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) {
--
cgit v1.2.3-70-g09d2