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Commit 603a148f authored by Mandeep Singh Baines's avatar Mandeep Singh Baines Committed by Ingo Molnar
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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: default avatarMandeep Singh Baines <msb@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent af432eb1

kernel/hung_task.c

+16 −8
Original line number Diff line number Diff line
@@ -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;