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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: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Mandeep Singh Baines 2009-01-17 10:31:48 -08:00 committed by Ingo Molnar
parent af432eb1cc
commit 603a148f43
1 changed files with 16 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
kernel/hung_task.c
View File

@ -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;