linux-kernel - [PATCH 3/7] watchdog/hardlockup: Declare arch_touch_nmi

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Message-Id: <20230607152432.5435-4-pmladek@suse.com>
Date:   Wed,  7 Jun 2023 17:24:28 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Douglas Anderson <dianders@...omium.org>
Cc:     kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        sparclinux@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        linux-perf-users@...r.kernel.org, Petr Mladek <pmladek@...e.com>
Subject: [PATCH 3/7] watchdog/hardlockup: Declare arch_touch_nmi_watchdog() only in linux/nmi.h

arch_touch_nmi_watchdog() needs a different implementation for various
hardlockup detector implementations. And it does nothing when
any hardlockup detector is not build at all.

arch_touch_nmi_watchdog() has to be declared in linux/nmi.h. It is done
directly in this header file for the perf and buddy detectors. And it
is done in the included asm/linux.h for arch specific detectors.

The reason probably is that the arch specific variants build the code
using another conditions. For example, powerpc64/sparc64 builds the code
when CONFIG_PPC_WATCHDOG is enabled.

Another reason might be that these architectures define more functions
in asm/nmi.h anyway.

However the generic code actually knows the information. The config
variables HAVE_NMI_WATCHDOG and HAVE_HARDLOCKUP_DETECTOR_ARCH are used
to decide whether to build the buddy detector.

In particular, CONFIG_HARDLOCKUP_DETECTOR is set only when a generic
or arch-specific hardlockup detector is built. The only exception
is sparc64 which ignores the global HARDLOCKUP_DETECTOR switch.

The information about sparc64 is a bit complicated. The hardlockup
detector is built there when CONFIG_HAVE_NMI_WATCHDOG is set and
CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH is not set.

People might wonder whether this change really makes things easier.
The motivation is:

  + The current logic in linux/nmi.h is far from obvious.
    For example, arch_touch_nmi_watchdog() is defined as {} when
    neither CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER nor
    CONFIG_HAVE_NMI_WATCHDOG is defined.

  + The change synchronizes the checks in lib/Kconfig.debug and
    in the generic code.

  + It is a step that will help cleaning HAVE_NMI_WATCHDOG related
    checks.

The change should not change the existing behavior.

Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 arch/powerpc/include/asm/nmi.h |  2 --
 arch/sparc/include/asm/nmi.h   |  1 -
 include/linux/nmi.h            | 13 ++++++++++---
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/nmi.h b/arch/powerpc/include/asm/nmi.h
index 43bfd4de868f..ce25318c3902 100644
--- a/arch/powerpc/include/asm/nmi.h
+++ b/arch/powerpc/include/asm/nmi.h
@@ -3,11 +3,9 @@
 #define _ASM_NMI_H
 
 #ifdef CONFIG_PPC_WATCHDOG
-extern void arch_touch_nmi_watchdog(void);
 long soft_nmi_interrupt(struct pt_regs *regs);
 void watchdog_hardlockup_set_timeout_pct(u64 pct);
 #else
-static inline void arch_touch_nmi_watchdog(void) {}
 static inline void watchdog_hardlockup_set_timeout_pct(u64 pct) {}
 #endif
 
diff --git a/arch/sparc/include/asm/nmi.h b/arch/sparc/include/asm/nmi.h
index 90ee7863d9fe..920dc23f443f 100644
--- a/arch/sparc/include/asm/nmi.h
+++ b/arch/sparc/include/asm/nmi.h
@@ -8,7 +8,6 @@ void nmi_adjust_hz(unsigned int new_hz);
 
 extern atomic_t nmi_active;
 
-void arch_touch_nmi_watchdog(void);
 void start_nmi_watchdog(void *unused);
 void stop_nmi_watchdog(void *unused);
 
diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index b5d0b7ab52fb..b9e816bde14a 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -7,6 +7,8 @@
 
 #include <linux/sched.h>
 #include <asm/irq.h>
+
+/* Arch specific watchdogs might need to share extra watchdog-related APIs. */
 #if defined(CONFIG_HAVE_NMI_WATCHDOG)
 #include <asm/nmi.h>
 #endif
@@ -89,12 +91,17 @@ extern unsigned int hardlockup_panic;
 static inline void hardlockup_detector_disable(void) {}
 #endif
 
-#if defined(CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER)
+/* Sparc64 has special implemetantion that is always enabled. */
+#if defined(CONFIG_HARDLOCKUP_DETECTOR) || \
+    (defined(CONFIG_HAVE_NMI_WATCHDOG) && !defined(CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH))
 void arch_touch_nmi_watchdog(void);
+#else
+static inline void arch_touch_nmi_watchdog(void) { }
+#endif
+
+#if defined(CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER)
 void watchdog_hardlockup_touch_cpu(unsigned int cpu);
 void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs);
-#elif !defined(CONFIG_HAVE_NMI_WATCHDOG)
-static inline void arch_touch_nmi_watchdog(void) { }
 #endif
 
 #if defined(CONFIG_HARDLOCKUP_DETECTOR_PERF)
-- 
2.35.3