linux-kernel - [PATCH v2 2/4] watchdog: export watchdog_mutex and lockup_detector

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Message-Id: <20220614135414.37746-3-ldufour@linux.ibm.com>
Date:   Tue, 14 Jun 2022 15:54:12 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        nathanl@...ux.ibm.com, haren@...ux.vnet.ibm.com, npiggin@...il.com
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/4] watchdog: export watchdog_mutex and lockup_detector_reconfigure

In some cricunstances 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, would prevent it to happen too frequently during LPM.

The watchdog_mutex is exported to allow some variable to be changed under
its protection and prevent any conflict.
The lockup_detector_reconfigure() function is exported and is expected to
be called under the protection of watchdog_mutex.

Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
---
 include/linux/nmi.h | 3 +++
 kernel/watchdog.c   | 6 +++---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index 750c7f395ca9..84300fb0f90a 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -122,6 +122,9 @@ int watchdog_nmi_probe(void);
 int watchdog_nmi_enable(unsigned int cpu);
 void watchdog_nmi_disable(unsigned int cpu);
 
+extern struct mutex watchdog_mutex;
+void lockup_detector_reconfigure(void);
+
 /**
  * touch_nmi_watchdog - restart NMI watchdog timeout.
  *
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 20a7a55e62b6..0a67a2dd1258 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -27,7 +27,7 @@
 #include <asm/irq_regs.h>
 #include <linux/kvm_para.h>
 
-static DEFINE_MUTEX(watchdog_mutex);
+DEFINE_MUTEX(watchdog_mutex);
 
 #if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)
 # define WATCHDOG_DEFAULT	(SOFT_WATCHDOG_ENABLED | NMI_WATCHDOG_ENABLED)
@@ -541,7 +541,7 @@ int lockup_detector_offline_cpu(unsigned int cpu)
 	return 0;
 }
 
-static void lockup_detector_reconfigure(void)
+void lockup_detector_reconfigure(void)
 {
 	cpus_read_lock();
 	watchdog_nmi_stop();
@@ -583,7 +583,7 @@ static __init void lockup_detector_setup(void)
 }
 
 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
-static void lockup_detector_reconfigure(void)
+void lockup_detector_reconfigure(void)
 {
 	cpus_read_lock();
 	watchdog_nmi_stop();
-- 
2.36.1