linux-kernel - [PATCH v4 2/4] watchdog: export lockup_detector

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Message-Id: <20220712143202.23144-3-ldufour@linux.ibm.com>
Date:   Tue, 12 Jul 2022 16:32:00 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
        wim@...ux-watchdog.org, linux@...ck-us.net, nathanl@...ux.ibm.com
Cc:     haren@...ux.vnet.ibm.com, hch@...radead.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-watchdog@...r.kernel.org
Subject: [PATCH v4 2/4] watchdog: export lockup_detector_reconfigure

In some circumstances it may be interesting to reconfigure the watchdog
from inside the kernel.

On PowerPC, this may helpful before and after a LPAR migration (LPM) is
initiated, because it implies some latencies, watchdog, and especially NMI
watchdog is expected to be triggered during this operation. Reconfiguring
the watchdog with a factor, would prevent it to happen too frequently
during LPM.

Rename lockup_detector_reconfigure() as __lockup_detector_reconfigure() and
create a new function lockup_detector_reconfigure() calling
__lockup_detector_reconfigure() under the protection of watchdog_mutex.

Cc: Christoph Hellwig <hch@...radead.org>
Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
---
 include/linux/nmi.h |  2 ++
 kernel/watchdog.c   | 21 ++++++++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index 750c7f395ca9..f700ff2df074 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -122,6 +122,8 @@ int watchdog_nmi_probe(void);
 int watchdog_nmi_enable(unsigned int cpu);
 void watchdog_nmi_disable(unsigned int cpu);
 
+void lockup_detector_reconfigure(void);
+
 /**
  * touch_nmi_watchdog - restart NMI watchdog timeout.
  *
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 20a7a55e62b6..90e6c41d5e33 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -541,7 +541,7 @@ int lockup_detector_offline_cpu(unsigned int cpu)
 	return 0;
 }
 
-static void lockup_detector_reconfigure(void)
+static void __lockup_detector_reconfigure(void)
 {
 	cpus_read_lock();
 	watchdog_nmi_stop();
@@ -561,6 +561,13 @@ static void lockup_detector_reconfigure(void)
 	__lockup_detector_cleanup();
 }
 
+void lockup_detector_reconfigure(void)
+{
+	mutex_lock(&watchdog_mutex);
+	__lockup_detector_reconfigure();
+	mutex_unlock(&watchdog_mutex);
+}
+
 /*
  * Create the watchdog infrastructure and configure the detector(s).
  */
@@ -577,13 +584,13 @@ static __init void lockup_detector_setup(void)
 		return;
 
 	mutex_lock(&watchdog_mutex);
-	lockup_detector_reconfigure();
+	__lockup_detector_reconfigure();
 	softlockup_initialized = true;
 	mutex_unlock(&watchdog_mutex);
 }
 
 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
-static void lockup_detector_reconfigure(void)
+void __lockup_detector_reconfigure(void)
 {
 	cpus_read_lock();
 	watchdog_nmi_stop();
@@ -591,9 +598,13 @@ static void lockup_detector_reconfigure(void)
 	watchdog_nmi_start();
 	cpus_read_unlock();
 }
+static inline void lockup_detector_reconfigure(void)
+{
+	__lockup_detector_reconfigure();
+}
 static inline void lockup_detector_setup(void)
 {
-	lockup_detector_reconfigure();
+	__lockup_detector_reconfigure();
 }
 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
 
@@ -633,7 +644,7 @@ static void proc_watchdog_update(void)
 {
 	/* Remove impossible cpus to keep sysctl output clean. */
 	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
-	lockup_detector_reconfigure();
+	__lockup_detector_reconfigure();
 }
 
 /*
-- 
2.37.0