linux-kernel - [PATCH 02/10] watchdog/hardlockup: HAVE_NMI_WATCHDOG must implement watchdog_hardlockup

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Message-ID: <20230526184139.2.Ic6ebbf307ca0efe91f08ce2c1eb4a037ba6b0700@changeid>
Date:   Fri, 26 May 2023 18:41:32 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.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,
        Douglas Anderson <dianders@...omium.org>
Subject: [PATCH 02/10] watchdog/hardlockup: HAVE_NMI_WATCHDOG must implement watchdog_hardlockup_probe()

Right now there is one arch (sparc64) that selects HAVE_NMI_WATCHDOG
without selecting HAVE_HARDLOCKUP_DETECTOR_ARCH. Because of that one
architecture, we have some special case code in the watchdog core to
handle the fact that watchdog_hardlockup_probe() isn't implemented.

Let's implement watchdog_hardlockup_probe() for sparc64 and get rid of
the special case.

As a side effect of doing this, code inspection tells us that we could
fix a minor bug where the system won't properly realize that NMI
watchdogs are disabled. Specifically, on powerpc if
CONFIG_PPC_WATCHDOG is turned off the arch might still select
CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH which selects
CONFIG_HAVE_NMI_WATCHDOG. Since CONFIG_PPC_WATCHDOG was off then
nothing will override the "weak" watchdog_hardlockup_probe() and we'll
fallback to looking at CONFIG_HAVE_NMI_WATCHDOG.

Suggested-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
Though this does fix a minor bug, I didn't mark this as "Fixes"
because it's super minor. One could also argue that this wasn't a bug
at all but simply was never an implemented feature. The code that
added some amount of dynamicness here was commit a994a3147e4c
("watchdog/hardlockup/perf: Implement init time detection of perf")
which, as per the title, was only intending to make "perf"
dynamic. The old NMI watchdog presumably has never been handled
dynamically.

 arch/Kconfig            |  3 ++-
 arch/sparc/kernel/nmi.c |  5 +++++
 kernel/watchdog.c       | 13 -------------
 3 files changed, 7 insertions(+), 14 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 64d771855ecd..b4f6387b12fe 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -428,7 +428,8 @@ config HAVE_NMI_WATCHDOG
 	bool
 	help
 	  The arch provides a low level NMI watchdog. It provides
-	  asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
+	  asm/nmi.h, and defines its own watchdog_hardlockup_probe() and
+	  arch_touch_nmi_watchdog().
 
 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 	bool
diff --git a/arch/sparc/kernel/nmi.c b/arch/sparc/kernel/nmi.c
index 9d9e29b75c43..17cdfdbf1f3b 100644
--- a/arch/sparc/kernel/nmi.c
+++ b/arch/sparc/kernel/nmi.c
@@ -65,6 +65,11 @@ void arch_touch_nmi_watchdog(void)
 }
 EXPORT_SYMBOL(arch_touch_nmi_watchdog);
 
+int __init watchdog_hardlockup_probe(void)
+{
+	return 0;
+}
+
 static void die_nmi(const char *str, struct pt_regs *regs, int do_panic)
 {
 	int this_cpu = smp_processor_id();
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 4b9e31edb47f..62230f5b8878 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -217,19 +217,6 @@ void __weak watchdog_hardlockup_disable(unsigned int cpu) { }
  */
 int __weak __init watchdog_hardlockup_probe(void)
 {
-	/*
-	 * If CONFIG_HAVE_NMI_WATCHDOG is defined then an architecture
-	 * is assumed to have the hard watchdog available and we return 0.
-	 */
-	if (IS_ENABLED(CONFIG_HAVE_NMI_WATCHDOG))
-		return 0;
-
-	/*
-	 * Hardlockup detectors other than those using CONFIG_HAVE_NMI_WATCHDOG
-	 * are required to implement a non-weak version of this probe function
-	 * to tell whether they are available. If they don't override then
-	 * we'll return -ENODEV.
-	 */
 	return -ENODEV;
 }
 
-- 
2.41.0.rc0.172.g3f132b7071-goog