linux-kernel - [PATCH] watchdog: Handle the ENODEV failure case of lockup_detector_delay

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Message-ID: <20240802151621.617244-1-longman@redhat.com>
Date: Fri,  2 Aug 2024 11:16:21 -0400
From: Waiman Long <longman@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Douglas Anderson <dianders@...omium.org>,
	Petr Mladek <pmladek@...e.com>,
	Li Zhe <lizhe.67@...edance.com>,
	Joel Granados <j.granados@...sung.com>,
	Thomas Weißschuh <linux@...ssschuh.net>
Cc: linux-kernel@...r.kernel.org,
	Waiman Long <longman@...hat.com>
Subject: [PATCH] watchdog: Handle the ENODEV failure case of lockup_detector_delay_init() separately

When watchdog_hardlockup_probe() is being called by
lockup_detector_delay_init(), an error return of -ENODEV will happen
for the arm64 arch when arch_perf_nmi_is_available() returns false. This
means that NMI is not usable by the hard lockup detector and so has to
be disabled. This can be considered a deficiency in that particular
arm64 chip, but there is nothing we can do about it.  That also means
the following error will always be reported when the kernel boot up.

  watchdog: Delayed init of the lockup detector failed: -19

The word "failed" itself has a connotation that there is something
wrong with the kernel which is not really the case here. Handle this
special ENODEV case separately and explain the reason behind disabling
hard lockup detector without causing anxiety for those users who read
the above message and wonder about it.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/watchdog.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 830a83895493..262691ba62b7 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -1203,7 +1203,10 @@ static void __init lockup_detector_delay_init(struct work_struct *work)

 	ret = watchdog_hardlockup_probe();
 	if (ret) {
-		pr_info("Delayed init of the lockup detector failed: %d\n", ret);
+		if (ret == -ENODEV)
+			pr_info("NMI not fully supported\n");
+		else
+			pr_info("Delayed init of the lockup detector failed: %d\n", ret);
 		pr_info("Hard watchdog permanently disabled\n");
 		return;
 	}
-- 
2.43.5