Message-Id: <20170518155026.23799-1-npiggin@gmail.com>
Date:   Fri, 19 May 2017 01:50:26 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Don Zickus <dzickus@...hat.com>
Cc:     Nicholas Piggin <npiggin@...il.com>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        adi-buildroot-devel@...ts.sourceforge.net,
        linux-am33-list@...hat.com, sparclinux@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: [RFC] arch hardlockup detector interfaces improvement

I'd like to make it easier for architectures that have their own NMI /
hard lockup detector to reuse various configuration interfaces that are
provided by generic detectors (cmdline, sysctl, suspend/resume calls).

I'd also like to remove the dependency of arch hard lockup detectors
on the softlockup detector. The reason being these watchdogs can be
very small (sparc's is like a page of core code that does not use any
big subsystem like kthreads or timers).

So I do this by adding a separate CONFIG_SOFTLOCKUP_DETECTOR, and
juggling around what goes under config options. HAVE_NMI_WATCHDOG
continues to be the config for arch to override the hard lockup
detector, which is expanded to cover a few more cases.

These config options are pretty ugly, but they already were. I don't
think they've become a lot worse after this.

Architectures can then use watchdog_nmi_reconfigure() which gets
called every time something changes (sysctls, suspend/resume, etc) and
adjust according to relevant parameters (watchdog_enabled,
watchdog_thresh, watchdog_cpumask, watchdog_suspended).

I have something for powerpc but I want to make sure this generic code
change is reasonable and could work for other archs.

Thanks,
Nick

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index aa3cd0878270..5c2265f84fa3 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -8,16 +8,25 @@
 #include <asm/irq.h>
 
 #ifdef CONFIG_LOCKUP_DETECTOR
+void lockup_detector_init(void);
+#else
+static inline void lockup_detector_init(void)
+{
+}
+#endif
+
+#ifdef CONFIG_SOFTLOCKUP_DETECTOR
+extern int proc_dowatchdog_thresh(struct ctl_table *table, int write,
+				  void __user *buffer,
+				  size_t *lenp, loff_t *ppos);
+
 extern void touch_softlockup_watchdog_sched(void);
 extern void touch_softlockup_watchdog(void);
 extern void touch_softlockup_watchdog_sync(void);
 extern void touch_all_softlockup_watchdogs(void);
-extern int proc_dowatchdog_thresh(struct ctl_table *table, int write,
-				  void __user *buffer,
-				  size_t *lenp, loff_t *ppos);
 extern unsigned int  softlockup_panic;
-extern unsigned int  hardlockup_panic;
-void lockup_detector_init(void);
+extern int soft_watchdog_enabled;
+extern atomic_t watchdog_park_in_progress;
 #else
 static inline void touch_softlockup_watchdog_sched(void)
 {
@@ -31,9 +40,6 @@ static inline void touch_softlockup_watchdog_sync(void)
 static inline void touch_all_softlockup_watchdogs(void)
 {
 }
-static inline void lockup_detector_init(void)
-{
-}
 #endif
 
 #ifdef CONFIG_DETECT_HUNG_TASK
@@ -70,17 +76,14 @@ static inline void reset_hung_task_detector(void)
  */
 #if defined(CONFIG_HAVE_NMI_WATCHDOG) || defined(CONFIG_HARDLOCKUP_DETECTOR)
 #include <asm/nmi.h>
+extern unsigned int hardlockup_panic;
 extern void touch_nmi_watchdog(void);
+extern void hardlockup_detector_disable(void);
 #else
 static inline void touch_nmi_watchdog(void)
 {
 	touch_softlockup_watchdog();
 }
-#endif
-
-#if defined(CONFIG_HARDLOCKUP_DETECTOR)
-extern void hardlockup_detector_disable(void);
-#else
 static inline void hardlockup_detector_disable(void) {}
 #endif
 
@@ -139,15 +142,18 @@ static inline bool trigger_single_cpu_backtrace(int cpu)
 }
 #endif
 
-#ifdef CONFIG_LOCKUP_DETECTOR
+#ifdef CONFIG_HARDLOCKUP_DETECTOR
 u64 hw_nmi_get_sample_period(int watchdog_thresh);
+#endif
+
+#ifdef CONFIG_LOCKUP_DETECTOR
 extern int nmi_watchdog_enabled;
-extern int soft_watchdog_enabled;
 extern int watchdog_user_enabled;
 extern int watchdog_thresh;
 extern unsigned long watchdog_enabled;
+extern struct cpumask watchdog_cpumask;
 extern unsigned long *watchdog_cpumask_bits;
-extern atomic_t watchdog_park_in_progress;
+extern int __read_mostly watchdog_suspended;
 #ifdef CONFIG_SMP
 extern int sysctl_softlockup_all_cpu_backtrace;
 extern int sysctl_hardlockup_all_cpu_backtrace;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4dfba1a76cc3..bb747d8f8521 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -880,6 +880,14 @@ static struct ctl_table kern_table[] = {
 #endif
 	},
 	{
+		.procname	= "watchdog_cpumask",
+		.data		= &watchdog_cpumask_bits,
+		.maxlen		= NR_CPUS,
+		.mode		= 0644,
+		.proc_handler	= proc_watchdog_cpumask,
+	},
+#ifdef CONFIG_SOFTLOCKUP_DETECTOR
+	{
 		.procname       = "soft_watchdog",
 		.data           = &soft_watchdog_enabled,
 		.maxlen         = sizeof (int),
@@ -889,13 +897,6 @@ static struct ctl_table kern_table[] = {
 		.extra2		= &one,
 	},
 	{
-		.procname	= "watchdog_cpumask",
-		.data		= &watchdog_cpumask_bits,
-		.maxlen		= NR_CPUS,
-		.mode		= 0644,
-		.proc_handler	= proc_watchdog_cpumask,
-	},
-	{
 		.procname	= "softlockup_panic",
 		.data		= &softlockup_panic,
 		.maxlen		= sizeof(int),
@@ -904,7 +905,8 @@ static struct ctl_table kern_table[] = {
 		.extra1		= &zero,
 		.extra2		= &one,
 	},
-#ifdef CONFIG_HARDLOCKUP_DETECTOR
+#endif
+#if defined(CONFIG_HAVE_NMI_WATCHDOG) || defined(CONFIG_HARDLOCKUP_DETECTOR)
 	{
 		.procname	= "hardlockup_panic",
 		.data		= &hardlockup_panic,
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 03e0b69bb5bf..192125f3f8aa 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -29,15 +29,54 @@
 #include <linux/kvm_para.h>
 #include <linux/kthread.h>
 
+/* Watchdog configuration */
 static DEFINE_MUTEX(watchdog_proc_mutex);
 
 #if defined(CONFIG_HAVE_NMI_WATCHDOG) || defined(CONFIG_HARDLOCKUP_DETECTOR)
 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED;
+int __read_mostly nmi_watchdog_enabled;
+
+/* boot commands */
+/*
+ * Should we panic when a soft-lockup or hard-lockup occurs:
+ */
+unsigned int __read_mostly hardlockup_panic =
+			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
+/*
+ * We may not want to enable hard lockup detection by default in all cases,
+ * for example when running the kernel as a guest on a hypervisor. In these
+ * cases this function can be called to disable hard lockup detection. This
+ * function should only be executed once by the boot processor before the
+ * kernel command line parameters are parsed, because otherwise it is not
+ * possible to override this in hardlockup_panic_setup().
+ */
+void hardlockup_detector_disable(void)
+{
+	watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
+}
+
+static int __init hardlockup_panic_setup(char *str)
+{
+	if (!strncmp(str, "panic", 5))
+		hardlockup_panic = 1;
+	else if (!strncmp(str, "nopanic", 7))
+		hardlockup_panic = 0;
+	else if (!strncmp(str, "0", 1))
+		watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
+	else if (!strncmp(str, "1", 1))
+		watchdog_enabled |= NMI_WATCHDOG_ENABLED;
+	return 1;
+}
+__setup("nmi_watchdog=", hardlockup_panic_setup);
+
 #else
 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
 #endif
-int __read_mostly nmi_watchdog_enabled;
+
+#ifdef CONFIG_SOFTLOCKUP_DETECTOR
 int __read_mostly soft_watchdog_enabled;
+#endif
+
 int __read_mostly watchdog_user_enabled;
 int __read_mostly watchdog_thresh = 10;
 
@@ -45,15 +84,9 @@ int __read_mostly watchdog_thresh = 10;
 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
 int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
 #endif
-static struct cpumask watchdog_cpumask __read_mostly;
+struct cpumask watchdog_cpumask __read_mostly;
 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
 
-/* Helper for online, unparked cpus. */
-#define for_each_watchdog_cpu(cpu) \
-	for_each_cpu_and((cpu), cpu_online_mask, &watchdog_cpumask)
-
-atomic_t watchdog_park_in_progress = ATOMIC_INIT(0);
-
 /*
  * The 'watchdog_running' variable is set to 1 when the watchdog threads
  * are registered/started and is set to 0 when the watchdog threads are
@@ -72,7 +105,32 @@ static int __read_mostly watchdog_running;
  * of 'watchdog_running' cannot change while the watchdog is deactivated
  * temporarily (see related code in 'proc' handlers).
  */
-static int __read_mostly watchdog_suspended;
+int __read_mostly watchdog_suspended;
+
+/*
+ * These functions can be overridden if an architecture implements its
+ * own hardlockup detector.
+ */
+int __weak watchdog_nmi_enable(unsigned int cpu)
+{
+	return 0;
+}
+void __weak watchdog_nmi_disable(unsigned int cpu)
+{
+}
+
+void __weak watchdog_nmi_reconfigure(void)
+{
+}
+
+
+#ifdef CONFIG_SOFTLOCKUP_DETECTOR
+
+/* Helper for online, unparked cpus. */
+#define for_each_watchdog_cpu(cpu) \
+	for_each_cpu_and((cpu), cpu_online_mask, &watchdog_cpumask)
+
+atomic_t watchdog_park_in_progress = ATOMIC_INIT(0);
 
 static u64 __read_mostly sample_period;
 
@@ -120,6 +178,7 @@ static int __init softlockup_all_cpu_backtrace_setup(char *str)
 	return 1;
 }
 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
+#ifdef CONFIG_HARDLOCKUP_DETECTOR
 static int __init hardlockup_all_cpu_backtrace_setup(char *str)
 {
 	sysctl_hardlockup_all_cpu_backtrace =
@@ -128,6 +187,7 @@ static int __init hardlockup_all_cpu_backtrace_setup(char *str)
 }
 __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
 #endif
+#endif
 
 /*
  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
@@ -213,18 +273,6 @@ void touch_softlockup_watchdog_sync(void)
 	__this_cpu_write(watchdog_touch_ts, 0);
 }
 
-/* watchdog detector functions */
-bool is_hardlockup(void)
-{
-	unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
-
-	if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
-		return true;
-
-	__this_cpu_write(hrtimer_interrupts_saved, hrint);
-	return false;
-}
-
 static int is_softlockup(unsigned long touch_ts)
 {
 	unsigned long now = get_timestamp();
@@ -237,21 +285,21 @@ static int is_softlockup(unsigned long touch_ts)
 	return 0;
 }
 
-static void watchdog_interrupt_count(void)
+/* watchdog detector functions */
+bool is_hardlockup(void)
 {
-	__this_cpu_inc(hrtimer_interrupts);
-}
+	unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 
-/*
- * These two functions are mostly architecture specific
- * defining them as weak here.
- */
-int __weak watchdog_nmi_enable(unsigned int cpu)
-{
-	return 0;
+	if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
+		return true;
+
+	__this_cpu_write(hrtimer_interrupts_saved, hrint);
+	return false;
 }
-void __weak watchdog_nmi_disable(unsigned int cpu)
+
+static void watchdog_interrupt_count(void)
 {
+	__this_cpu_inc(hrtimer_interrupts);
 }
 
 static int watchdog_enable_all_cpus(void);
@@ -502,57 +550,6 @@ static void watchdog_unpark_threads(void)
 		kthread_unpark(per_cpu(softlockup_watchdog, cpu));
 }
 
-/*
- * Suspend the hard and soft lockup detector by parking the watchdog threads.
- */
-int lockup_detector_suspend(void)
-{
-	int ret = 0;
-
-	get_online_cpus();
-	mutex_lock(&watchdog_proc_mutex);
-	/*
-	 * Multiple suspend requests can be active in parallel (counted by
-	 * the 'watchdog_suspended' variable). If the watchdog threads are
-	 * running, the first caller takes care that they will be parked.
-	 * The state of 'watchdog_running' cannot change while a suspend
-	 * request is active (see related code in 'proc' handlers).
-	 */
-	if (watchdog_running && !watchdog_suspended)
-		ret = watchdog_park_threads();
-
-	if (ret == 0)
-		watchdog_suspended++;
-	else {
-		watchdog_disable_all_cpus();
-		pr_err("Failed to suspend lockup detectors, disabled\n");
-		watchdog_enabled = 0;
-	}
-
-	mutex_unlock(&watchdog_proc_mutex);
-
-	return ret;
-}
-
-/*
- * Resume the hard and soft lockup detector by unparking the watchdog threads.
- */
-void lockup_detector_resume(void)
-{
-	mutex_lock(&watchdog_proc_mutex);
-
-	watchdog_suspended--;
-	/*
-	 * The watchdog threads are unparked if they were previously running
-	 * and if there is no more active suspend request.
-	 */
-	if (watchdog_running && !watchdog_suspended)
-		watchdog_unpark_threads();
-
-	mutex_unlock(&watchdog_proc_mutex);
-	put_online_cpus();
-}
-
 static int update_watchdog_all_cpus(void)
 {
 	int ret;
@@ -604,6 +601,96 @@ static void watchdog_disable_all_cpus(void)
 	}
 }
 
+static int watchdog_update_cpus(void)
+{
+	return smpboot_update_cpumask_percpu_thread(
+		    &watchdog_threads, &watchdog_cpumask);
+}
+
+#else /* SOFTLOCKUP */
+static int watchdog_park_threads(void)
+{
+	return 0;
+}
+
+static void watchdog_unpark_threads(void)
+{
+}
+
+static int watchdog_enable_all_cpus(void)
+{
+	return 0;
+}
+
+static void watchdog_disable_all_cpus(void)
+{
+}
+
+static int watchdog_update_cpus(void)
+{
+	return 0;
+}
+
+static void set_sample_period(void)
+{
+}
+#endif /* SOFTLOCKUP */
+
+/*
+ * Suspend the hard and soft lockup detector by parking the watchdog threads.
+ */
+int lockup_detector_suspend(void)
+{
+	int ret = 0;
+
+	get_online_cpus();
+	mutex_lock(&watchdog_proc_mutex);
+	/*
+	 * Multiple suspend requests can be active in parallel (counted by
+	 * the 'watchdog_suspended' variable). If the watchdog threads are
+	 * running, the first caller takes care that they will be parked.
+	 * The state of 'watchdog_running' cannot change while a suspend
+	 * request is active (see related code in 'proc' handlers).
+	 */
+	if (watchdog_running && !watchdog_suspended)
+		ret = watchdog_park_threads();
+
+	if (ret == 0)
+		watchdog_suspended++;
+	else {
+		watchdog_disable_all_cpus();
+		pr_err("Failed to suspend lockup detectors, disabled\n");
+		watchdog_enabled = 0;
+	}
+
+	watchdog_nmi_reconfigure();
+
+	mutex_unlock(&watchdog_proc_mutex);
+
+	return ret;
+}
+
+/*
+ * Resume the hard and soft lockup detector by unparking the watchdog threads.
+ */
+void lockup_detector_resume(void)
+{
+	mutex_lock(&watchdog_proc_mutex);
+
+	watchdog_suspended--;
+	/*
+	 * The watchdog threads are unparked if they were previously running
+	 * and if there is no more active suspend request.
+	 */
+	if (watchdog_running && !watchdog_suspended)
+		watchdog_unpark_threads();
+
+	watchdog_nmi_reconfigure();
+
+	mutex_unlock(&watchdog_proc_mutex);
+	put_online_cpus();
+}
+
 #ifdef CONFIG_SYSCTL
 
 /*
@@ -625,6 +712,8 @@ static int proc_watchdog_update(void)
 	else
 		watchdog_disable_all_cpus();
 
+	watchdog_nmi_reconfigure();
+
 	return err;
 
 }
@@ -810,10 +899,11 @@ int proc_watchdog_cpumask(struct ctl_table *table, int write,
 			 * a temporary cpumask, so we are likely not in a
 			 * position to do much else to make things better.
 			 */
-			if (smpboot_update_cpumask_percpu_thread(
-				    &watchdog_threads, &watchdog_cpumask) != 0)
+			if (watchdog_update_cpus() != 0)
 				pr_err("cpumask update failed\n");
 		}
+
+		watchdog_nmi_reconfigure();
 	}
 out:
 	mutex_unlock(&watchdog_proc_mutex);
diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index 54a427d1f344..2b328d6c0bc8 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -22,39 +22,7 @@ static DEFINE_PER_CPU(bool, hard_watchdog_warn);
 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
 
-/* boot commands */
-/*
- * Should we panic when a soft-lockup or hard-lockup occurs:
- */
-unsigned int __read_mostly hardlockup_panic =
-			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
 static unsigned long hardlockup_allcpu_dumped;
-/*
- * We may not want to enable hard lockup detection by default in all cases,
- * for example when running the kernel as a guest on a hypervisor. In these
- * cases this function can be called to disable hard lockup detection. This
- * function should only be executed once by the boot processor before the
- * kernel command line parameters are parsed, because otherwise it is not
- * possible to override this in hardlockup_panic_setup().
- */
-void hardlockup_detector_disable(void)
-{
-	watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
-}
-
-static int __init hardlockup_panic_setup(char *str)
-{
-	if (!strncmp(str, "panic", 5))
-		hardlockup_panic = 1;
-	else if (!strncmp(str, "nopanic", 7))
-		hardlockup_panic = 0;
-	else if (!strncmp(str, "0", 1))
-		watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
-	else if (!strncmp(str, "1", 1))
-		watchdog_enabled |= NMI_WATCHDOG_ENABLED;
-	return 1;
-}
-__setup("nmi_watchdog=", hardlockup_panic_setup);
 
 void touch_nmi_watchdog(void)
 {
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e4587ebe52c7..68685d3ddac0 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -801,14 +801,18 @@ config LOCKUP_DETECTOR
 	  The frequency of hrtimer and NMI events and the soft and hard lockup
 	  thresholds can be controlled through the sysctl watchdog_thresh.
 
+config SOFTLOCKUP_DETECTOR
+	bool "Detect Soft Lockups"
+	depends on LOCKUP_DETECTOR
+
 config HARDLOCKUP_DETECTOR
-	def_bool y
-	depends on LOCKUP_DETECTOR && !HAVE_NMI_WATCHDOG
+	bool "Detect Hard Lockups"
+	depends on SOFTLOCKUP_DETECTOR && !HAVE_NMI_WATCHDOG
 	depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI
 
 config BOOTPARAM_HARDLOCKUP_PANIC
 	bool "Panic (Reboot) On Hard Lockups"
-	depends on HARDLOCKUP_DETECTOR
+	depends on HARDLOCKUP_DETECTOR || HAVE_NMI_WATCHDOG
 	help
 	  Say Y here to enable the kernel to panic on "hard lockups",
 	  which are bugs that cause the kernel to loop in kernel
@@ -819,14 +823,14 @@ config BOOTPARAM_HARDLOCKUP_PANIC
 
 config BOOTPARAM_HARDLOCKUP_PANIC_VALUE
 	int
-	depends on HARDLOCKUP_DETECTOR
+	depends on HARDLOCKUP_DETECTOR || HAVE_NMI_WATCHDOG
 	range 0 1
 	default 0 if !BOOTPARAM_HARDLOCKUP_PANIC
 	default 1 if BOOTPARAM_HARDLOCKUP_PANIC
 
 config BOOTPARAM_SOFTLOCKUP_PANIC
 	bool "Panic (Reboot) On Soft Lockups"
-	depends on LOCKUP_DETECTOR
+	depends on SOFTLOCKUP_DETECTOR
 	help
 	  Say Y here to enable the kernel to panic on "soft lockups",
 	  which are bugs that cause the kernel to loop in kernel
@@ -843,7 +847,7 @@ config BOOTPARAM_SOFTLOCKUP_PANIC
 
 config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
 	int
-	depends on LOCKUP_DETECTOR
+	depends on SOFTLOCKUP_DETECTOR
 	range 0 1
 	default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC
 	default 1 if BOOTPARAM_SOFTLOCKUP_PANIC
@@ -851,7 +855,7 @@ config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
 config DETECT_HUNG_TASK
 	bool "Detect Hung Tasks"
 	depends on DEBUG_KERNEL
-	default LOCKUP_DETECTOR
+	default SOFTLOCKUP_DETECTOR
 	help
 	  Say Y here to enable the kernel to detect "hung tasks",
 	  which are bugs that cause the task to be stuck in
-- 
2.11.0

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