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Commit baf48f65 authored by Mandeep Singh Baines's avatar Mandeep Singh Baines Committed by Ingo Molnar
Browse files

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: default avatarMandeep Singh Baines <msb@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent e4fa4c97

include/linux/sched.h

+3 −0
Original line number Diff line number Diff line
@@ -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;

kernel/softlockup.c

+9 −0
Original line number Diff line number Diff line
@@ -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:

kernel/sysctl.c

+1 −1
Original line number Diff line number Diff line
@@ -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,