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>
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index ba5a77c..ba8ccd4 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -72,7 +72,8 @@
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 @@
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 @@
* 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 @@
* 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 @@
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 @@
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;
