softlockup: add a /proc tuning parameter

Control the trigger limit for softlockup warnings.  This is useful for
debugging softlockups, by lowering the softlockup_thresh to identify
possible softlockups earlier.

This patch:
1. Adds a sysctl softlockup_thresh with valid values of 1-60s
   (Higher value to disable false positives)
2. Changes the softlockup printk to print the cpu softlockup time

[akpm@linux-foundation.org: Fix various warnings and add definition of "two"]
Signed-off-by: NRavikiran Thirumalai <kiran@scalex86.org>
Signed-off-by: NShai Fultheim <shai@scalex86.org>
Acked-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/sysctl/kernel.txt

@@ -320,6 +320,14 @@ kernel.  This value defaults to SHMMAX.
 
 ==============================================================
 
+softlockup_thresh:
+
+This value can be used to lower the softlockup tolerance
+threshold. The default threshold is 10s.  If a cpu is locked up
+for 10s, the kernel complains.  Valid values are 1-60s.
+
+==============================================================
+
 tainted: 
 
 Non-zero if the kernel has been tainted.  Numeric values, which

include/linux/sched.h

@@ -261,6 +261,7 @@ extern void softlockup_tick(void);
 extern void spawn_softlockup_task(void);
 extern void touch_softlockup_watchdog(void);
 extern void touch_all_softlockup_watchdogs(void);
+extern int softlockup_thresh;
 #else
 static inline void softlockup_tick(void)
 {

kernel/softlockup.c

@@ -24,6 +24,7 @@ static DEFINE_PER_CPU(unsigned long, print_timestamp);
 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
 
 static int did_panic;
+int softlockup_thresh = 10;
 
 static int
 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
@@ -104,13 +105,15 @@ void softlockup_tick(void)
 		wake_up_process(per_cpu(watchdog_task, this_cpu));
 
 	/* Warn about unreasonable 10+ seconds delays: */
-	if (now <= (touch_timestamp + 10))
+	if (now <= (touch_timestamp + softlockup_thresh))
 		return;
 
 	per_cpu(print_timestamp, this_cpu) = touch_timestamp;
 
 	spin_lock(&print_lock);
-	printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n", this_cpu);
+	printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
+			this_cpu, now - touch_timestamp,
+				current->comm, current->pid);
 	if (regs)
 		show_regs(regs);
 	else

kernel/sysctl.c

@@ -80,6 +80,19 @@ extern int maps_protect;
 extern int sysctl_stat_interval;
 extern int audit_argv_kb;
 
+/* Constants used for minimum and  maximum */
+#ifdef CONFIG_DETECT_SOFTLOCKUP
+static int one = 1;
+static int sixty = 60;
+#endif
+
+#ifdef CONFIG_MMU
+static int two = 2;
+#endif
+
+static int zero;
+static int one_hundred = 100;
+
 /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
 static int maxolduid = 65535;
 static int minolduid;
@@ -711,6 +724,19 @@ static ctl_table kern_table[] = {
 		.proc_handler	= &proc_dointvec,
 	},
 #endif
+#ifdef CONFIG_DETECT_SOFTLOCKUP
+	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "softlockup_thresh",
+		.data		= &softlockup_thresh,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec_minmax,
+		.strategy	= &sysctl_intvec,
+		.extra1		= &one,
+		.extra2		= &sixty,
+	},
+#endif
 #ifdef CONFIG_COMPAT
 	{
 		.ctl_name	= KERN_COMPAT_LOG,
@@ -757,13 +783,6 @@ static ctl_table kern_table[] = {
 	{ .ctl_name = 0 }
 };
 
-/* Constants for minimum and maximum testing in vm_table.
-   We use these as one-element integer vectors. */
-static int zero;
-static int two = 2;
-static int one_hundred = 100;
-
-
 static ctl_table vm_table[] = {
 	{
 		.ctl_name	= VM_OVERCOMMIT_MEMORY,