disable softlockup detection at boottime

This patch allows softlockup detection to be disabled by specifying a boottime parameter.

Signed-off-by Dimitri Sivanich <[email protected]>

Index: linux/kernel/softlockup.c
===================================================================

kernel/softlockup.c +12 -1

@@ -24,6 +24,7 @@ static DEFINE_PER_CPU(unsigned long, tou
 static DEFINE_PER_CPU(unsigned long, print_timestamp);
 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
 
+static int __read_mostly softlockup_off;
 static int __read_mostly did_panic;
 unsigned long __read_mostly softlockup_thresh = 60;
 

@@ -53,7 +54,8 @@ void touch_softlockup_watchdog(void)
 {
 	int this_cpu = raw_smp_processor_id();
 
-	__raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
+	if (!softlockup_off)
+		__raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
 }
 EXPORT_SYMBOL(touch_softlockup_watchdog);
 

@@ -61,6 +63,9 @@ void touch_all_softlockup_watchdogs(void
 {
 	int cpu;
 
+	if (softlockup_off)
+		return;
+
 	/* Cause each CPU to re-update its timestamp rather than complain */
 	for_each_online_cpu(cpu)
 		per_cpu(touch_timestamp, cpu) = 0;

@@ -79,6 +84,9 @@ void softlockup_tick(void)
 	struct pt_regs *regs = get_irq_regs();
 	unsigned long now;
 
+	if (softlockup_off)
+		return;
+
 	if (touch_timestamp == 0) {
 		touch_softlockup_watchdog();
 		return;

@@ -306,9 +314,19 @@ __init void spawn_softlockup_task(void)
 	void *cpu = (void *)(long)smp_processor_id();
 	int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 
+	if (softlockup_off)
+		return;
+
 	BUG_ON(err == NOTIFY_BAD);
 	cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 	register_cpu_notifier(&cpu_nfb);
 

(b) entry in Documentation/kernel-parameters.txt

This patch allows softlockup detection to be disabled by specifying a boottime parameter.

good idea - but why dont you set softlockup_thresh to 0, which is the "off" switch already? (and that way it can be turned back on later as well, by the sysadmin.)

Quoted 5 lines · Ingo Molnar

good idea - but why dont you set softlockup_thresh to 0, which is the "off" switch already? (and that way it can be turned back on later as well, by the sysadmin.)

I'm getting unaligned access errors trying to set it to anything, so it's not working for me currently (2.6.25):

It's tripping up on the address of 'one', which is an int that is not properly aligned for the unsigned long comparison in proc_doulongvec_minmax on my 64 bit machine. Also, the value '0' is invalid for softlockup_thresh, correct?

I temporarily got around these issues with the following hack.

Quoted 8 lines · Dimitri Sivanich

I'm getting unaligned access errors trying to set it to anything, so it's not working for me currently (2.6.25):

It's tripping up on the address of 'one', which is an int that is not properly aligned for the unsigned long comparison in proc_doulongvec_minmax on my 64 bit machine. Also, the value '0' is invalid for softlockup_thresh, correct?

Quoted 1 line

I temporarily got around these issues with the following hack.

ah, sorry. But ... perhaps using threshold -1 would be the most intuitive setting? (for 'infinite timeout' ==> softlockup detector turned off) That way it all becomes configurable as part of the threshold? No strong opinion though.

Quoted 4 lines

ah, sorry. But ... perhaps using threshold -1 would be the most intuitive setting? (for 'infinite timeout' ==> softlockup detector turned off) That way it all becomes configurable as part of the threshold? No strong opinion though.

Having the ability to switch it off dynamically would be nice to have, but will need a little work yet. Any solution should also minimize the amount of time spent in softlockup_tick.

Either '0' or '-1' seems OK to me, but if '-1' turns it off, do we allow a value of '0'?.