[PATCH v7 23/24] watchdog: Introduce hardlockup_detector_mark_unavailable()

[Ricardo Neri]

The NMI watchdog may become unreliable during runtime. This is the case
in x86 if, for instance, the HPET-based hardlockup detector is in use and
the TSC counter becomes unstable.

Introduce a new interface to mark the hardlockup detector as unavailable
in such cases. When doing this, update the state of /proc/sys/kernel/
nmi_watchdog to keep it consistent.

Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>
Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
Changes since v6:
 * Introduced this patch

Changes since v5:
 * N/A

Changes since v4
 * N/A

Changes since v3
 * N/A

Changes since v2:
 * N/A

Changes since v1:
 * N/A
---
 include/linux/nmi.h |  2 ++
 kernel/watchdog.c   | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index a38c4509f9eb..40a97139ec65 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -83,9 +83,11 @@ static inline void reset_hung_task_detector(void) { }
 
 #if defined(CONFIG_HARDLOCKUP_DETECTOR)
 extern void hardlockup_detector_disable(void);
+extern void hardlockup_detector_mark_unavailable(void);
 extern unsigned int hardlockup_panic;
 #else
 static inline void hardlockup_detector_disable(void) {}
+static inline void hardlockup_detector_mark_unavailable(void) {}
 #endif
 
 #if defined(CONFIG_HAVE_NMI_WATCHDOG) || defined(CONFIG_HARDLOCKUP_DETECTOR)
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 8e61f21e7e33..0e4fed6d95b9 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -47,6 +47,8 @@ static int __read_mostly nmi_watchdog_available;
 struct cpumask watchdog_cpumask __read_mostly;
 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
 
+static void __lockup_detector_reconfigure(void);
+
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 
 # ifdef CONFIG_SMP
@@ -85,6 +87,24 @@ static int __init hardlockup_panic_setup(char *str)
 }
 __setup("nmi_watchdog=", hardlockup_panic_setup);
 
+/**
+ * hardlockup_detector_mark_unavailable - Mark the NMI watchdog as unavailable
+ *
+ * Indicate that the hardlockup detector has become unavailable. This may
+ * happen if the hardware resources that the detector uses have become
+ * unreliable.
+ */
+void hardlockup_detector_mark_unavailable(void)
+{
+	mutex_lock(&watchdog_mutex);
+
+	/* These variables can be updated without stopping the detector. */
+	nmi_watchdog_user_enabled = 0;
+	nmi_watchdog_available = false;
+
+	__lockup_detector_reconfigure();
+	mutex_unlock(&watchdog_mutex);
+}
 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 
 /*
-- 
2.25.1