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>

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>
Mandeep Singh Baines · Ingo Molnar
1 parent e4fa4c9701
Showing 3 changed files with 13 additions and 1 deletions Side-by-side Diff
include/linux/sched.h
kernel/softlockup.c
kernel/sysctl.c
@@ -293,6 +293,9 @@
 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;
@@ -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>
  
@@ -87,6 +88,14 @@
 		per_cpu(touch_timestamp, cpu) = 0;
 }
 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
@@ -800,7 +800,7 @@
 		.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,
...	...	@@ -293,6 +293,9 @@
293	293	extern void softlockup_tick(void);
294	294	extern void touch_softlockup_watchdog(void);
295	295	extern void touch_all_softlockup_watchdogs(void);
	296	+extern int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
	297	+ struct file filp, void __user buffer,
	298	+ size_t lenp, loff_t ppos);
296	299	extern unsigned int softlockup_panic;
297	300	extern unsigned long sysctl_hung_task_check_count;
298	301	extern unsigned long sysctl_hung_task_timeout_secs;
...	...	@@ -16,6 +16,7 @@
16	16	#include <linux/lockdep.h>
17	17	#include <linux/notifier.h>
18	18	#include <linux/module.h>
	19	+#include <linux/sysctl.h>
19	20
20	21	#include <asm/irq_regs.h>
21	22
...	...	@@ -87,6 +88,14 @@
87	88	per_cpu(touch_timestamp, cpu) = 0;
88	89	}
89	90	EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
	91	+
	92	+int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
	93	+ struct file filp, void __user buffer,
	94	+ size_t lenp, loff_t ppos)
	95	+{
	96	+ touch_all_softlockup_watchdogs();
	97	+ return proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
	98	+}
90	99
91	100	/*
92	101	* This callback runs from the timer interrupt, and checks
...	...	@@ -800,7 +800,7 @@
800	800	.data = &softlockup_thresh,
801	801	.maxlen = sizeof(int),
802	802	.mode = 0644,
803		- .proc_handler = &proc_dointvec_minmax,
	803	+ .proc_handler = &proc_dosoftlockup_thresh,
804	804	.strategy = &sysctl_intvec,
805	805	.extra1 = &neg_one,
806	806	.extra2 = &sixty,