softlockup: fix softlockup_thresh unaligned access and disable detection at runtime

Fix unaligned access errors when setting softlockup_thresh on
64 bit platforms.

Allow softlockup detection to be disabled by setting
softlockup_thresh <= 0.

Detect that boot time softlockup detection has been disabled
earlier in softlockup_tick.

Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

3 files changed, 16 insertions, 7 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 71f5972dc48e..ea26221644e2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -295,10 +295,10 @@ extern void spawn_softlockup_task(void);
 extern void touch_softlockup_watchdog(void);
 extern void touch_all_softlockup_watchdogs(void);
 extern unsigned int  softlockup_panic;
-extern unsigned long softlockup_thresh;
 extern unsigned long sysctl_hung_task_check_count;
 extern unsigned long sysctl_hung_task_timeout_secs;
 extern unsigned long sysctl_hung_task_warnings;
+extern int softlockup_thresh;
 #else
 static inline void softlockup_tick(void)
 {
diff --git a/kernel/softlockup.c b/kernel/softlockup.c
index 78e0ad21cb0c..a3a0b239b7f7 100644
--- a/kernel/softlockup.c
+++ b/kernel/softlockup.c
@@ -25,7 +25,7 @@ static DEFINE_PER_CPU(unsigned long, print_timestamp);
 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
 
 static int __read_mostly did_panic;
-unsigned long __read_mostly softlockup_thresh = 60;
+int __read_mostly softlockup_thresh = 60;
 
 /*
  * Should we panic (and reboot, if panic_timeout= is set) when a
@@ -94,6 +94,14 @@ void softlockup_tick(void)
         struct pt_regs *regs = get_irq_regs();
         unsigned long now;
 
+        /* Is detection switched off? */
+        if (!per_cpu(watchdog_task, this_cpu) || softlockup_thresh <= 0) {
+                /* Be sure we don't false trigger if switched back on */
+                if (touch_timestamp)
+                        per_cpu(touch_timestamp, this_cpu) = 0;
+                return;
+        }
+
         if (touch_timestamp == 0) {
                 touch_softlockup_watchdog();
                 return;
@@ -104,7 +112,7 @@ void softlockup_tick(void)
         /* report at most once a second */
         if ((print_timestamp >= touch_timestamp &&
                         print_timestamp < (touch_timestamp + 1)) ||
-                        did_panic || !per_cpu(watchdog_task, this_cpu)) {
+                        did_panic) {
                 return;
         }
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 2d3b388c402d..31c19a79738d 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -84,12 +84,13 @@ extern int latencytop_enabled;
 extern int sysctl_nr_open_min, sysctl_nr_open_max;
 
 /* Constants used for minimum and  maximum */
-#if defined(CONFIG_DETECT_SOFTLOCKUP) || defined(CONFIG_HIGHMEM)
+#ifdef CONFIG_HIGHMEM
 static int one = 1;
 #endif
 
 #ifdef CONFIG_DETECT_SOFTLOCKUP
 static int sixty = 60;
+static int neg_one = -1;
 #endif
 
 #ifdef CONFIG_MMU
@@ -742,11 +743,11 @@ static struct ctl_table kern_table[] = {
                 .ctl_name       = CTL_UNNUMBERED,
                 .procname       = "softlockup_thresh",
                 .data           = &softlockup_thresh,
-                .maxlen         = sizeof(unsigned long),
+                .maxlen         = sizeof(int),
                 .mode           = 0644,
-                .proc_handler   = &proc_doulongvec_minmax,
+                .proc_handler   = &proc_dointvec_minmax,
                 .strategy       = &sysctl_intvec,
-                .extra1         = &one,
+                .extra1         = &neg_one,
                 .extra2         = &sixty,
         },
         {