2009-01-13 05:33:34

by Mandeep Baines

Subject: [PATCH] softlock: fix false panic which can occur if softlockup_thresh is reduced

At run-time, if softlockup_thresh is changed to a much lower value,
touch_timestamp is likely to be much older than the new softlock_thresh.

This will cause a false softlockup to be detected. If softlockup_panic
is enabled, the system will panic.

The fix is to touch all watchdogs before changing softlockup_thresh.

Signed-off-by: Mandeep Singh Baines <[email protected]>
---
include/linux/sched.h | 3 +++
kernel/softlockup.c | 9 +++++++++
kernel/sysctl.c | 2 +-
3 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 55e30d1..cd4a9f6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -295,6 +295,9 @@ extern void sched_show_task(struct task_struct *p);
extern void softlockup_tick(void);
extern void touch_softlockup_watchdog(void);
extern void touch_all_softlockup_watchdogs(void);
+extern int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
+ struct file *filp, void __user *buffer,
+ size_t *lenp, loff_t *ppos);
extern unsigned int softlockup_panic;
extern unsigned long sysctl_hung_task_check_count;
extern unsigned long sysctl_hung_task_timeout_secs;
diff --git a/kernel/softlockup.c b/kernel/softlockup.c
index dc0b3be..2d850e1 100644
--- a/kernel/softlockup.c
+++ b/kernel/softlockup.c
@@ -16,6 +16,7 @@
#include <linux/lockdep.h>
#include <linux/notifier.h>
#include <linux/module.h>
+#include <linux/sysctl.h>

#include <asm/irq_regs.h>

@@ -88,6 +89,14 @@ void touch_all_softlockup_watchdogs(void)
}
EXPORT_SYMBOL(touch_all_softlockup_watchdogs);

+int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
+ struct file *filp, void __user *buffer,
+ size_t *lenp, loff_t *ppos)
+{
+ touch_all_softlockup_watchdogs();
+ return proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
+}
+
/*
* This callback runs from the timer interrupt, and checks
* whether the watchdog thread has hung or not:
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 3d56fe7..a3d5828 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -766,7 +766,7 @@ static struct ctl_table kern_table[] = {
.data = &softlockup_thresh,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = &proc_dointvec_minmax,
+ .proc_handler = &proc_dosoftlockup_thresh,
.strategy = &sysctl_intvec,
.extra1 = &neg_one,
.extra2 = &sixty,
--
1.5.4.5

2009-01-14 10:48:57

by Ingo Molnar

Subject: Re: [PATCH] softlock: fix false panic which can occur if softlockup_thresh is reduced

* Mandeep Singh Baines <[email protected]> wrote:

> At run-time, if softlockup_thresh is changed to a much lower value,
> touch_timestamp is likely to be much older than the new softlock_thresh.
>
> This will cause a false softlockup to be detected. If softlockup_panic
> is enabled, the system will panic.
>
> The fix is to touch all watchdogs before changing softlockup_thresh.
>
> Signed-off-by: Mandeep Singh Baines <[email protected]>
> ---
> include/linux/sched.h | 3 +++
> kernel/softlockup.c | 9 +++++++++
> kernel/sysctl.c | 2 +-
> 3 files changed, 13 insertions(+), 1 deletions(-)

applied to tip/core/urgent, thanks!

Ingo