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 <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4cae9b8..54cbabf 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -293,6 +293,9 @@ 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 d9188c6..85d5a24 100644 (file)
--- 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 89d7443..596dc31 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -800,7 +800,7 @@ 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,