linux-kernel - [PATCH v2 9/9] watchdog: skip checks when panic is in progress

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Message-ID: <20250825022947.1596226-10-wangjinchao600@gmail.com>
Date: Mon, 25 Aug 2025 10:29:37 +0800
From: Jinchao Wang <wangjinchao600@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>,
	Yury Norov <yury.norov@...il.com>,
	Qianqiang Liu <qianqiang.liu@....com>,
	Simona Vetter <simona@...ll.ch>,
	Helge Deller <deller@....de>,
	Petr Mladek <pmladek@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Dave Young <dyoung@...hat.com>,
	Kees Cook <kees@...nel.org>,
	Tony Luck <tony.luck@...el.com>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Shixiong Ou <oushixiong@...inos.cn>,
	Jinchao Wang <wangjinchao600@...il.com>,
	Zsolt Kajtar <soci@....rulez.org>,
	Ingo Molnar <mingo@...nel.org>,
	Nam Cao <namcao@...utronix.de>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Joel Granados <joel.granados@...nel.org>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Sohil Mehta <sohil.mehta@...el.com>,
	Feng Tang <feng.tang@...ux.alibaba.com>,
	Sravan Kumar Gundu <sravankumarlpu@...il.com>,
	Douglas Anderson <dianders@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Anna Schumaker <anna.schumaker@...cle.com>,
	"Darrick J. Wong" <djwong@...nel.org>,
	Max Kellermann <max.kellermann@...os.com>,
	Yunhui Cui <cuiyunhui@...edance.com>,
	Tejun Heo <tj@...nel.org>,
	Luo Gengkun <luogengkun@...weicloud.com>,
	Li Huafei <lihuafei1@...wei.com>,
	Thorsten Blum <thorsten.blum@...ux.dev>,
	Yicong Yang <yangyicong@...ilicon.com>,
	linux-fbdev@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	kexec@...ts.infradead.org,
	linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 9/9] watchdog: skip checks when panic is in progress

This issue was found when an EFI pstore was configured for kdump
logging with the NMI hard lockup detector enabled. The efi-pstore
write operation was slow, and with a large number of logs, the
pstore dump callback within kmsg_dump() took a long time.

This delay triggered the NMI watchdog, leading to a nested panic.
The call flow demonstrates how the secondary panic caused an
emergency_restart() to be triggered before the initial pstore
operation could finish, leading to a failure to dump the logs:

  real panic() {
	kmsg_dump() {
		...
		pstore_dump() {
			start_dump();
			... // long time operation triggers NMI watchdog
			nmi panic() {
				...
				emergency_restart(); // pstore unfinished
			}
			...
			finish_dump(); // never reached
		}
	}
  }

Both watchdog_buddy_check_hardlockup() and watchdog_overflow_callback() may
trigger during a panic. This can lead to recursive panic handling.

Add panic_in_progress() checks so watchdog activity is skipped once a panic
has begun.

This prevents recursive panic and keeps the panic path more reliable.

Signed-off-by: Jinchao Wang <wangjinchao600@...il.com>
Reviewed-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
---
 kernel/watchdog.c      | 6 ++++++
 kernel/watchdog_perf.c | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 80b56c002c7f..597c0d947c93 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -740,6 +740,12 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 	if (!watchdog_enabled)
 		return HRTIMER_NORESTART;
 
+	/*
+	 * pass the buddy check if a panic is in process
+	 */
+	if (panic_in_progress())
+		return HRTIMER_NORESTART;
+
 	watchdog_hardlockup_kick();
 
 	/* kick the softlockup detector */
diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c
index 9c58f5b4381d..d3ca70e3c256 100644
--- a/kernel/watchdog_perf.c
+++ b/kernel/watchdog_perf.c
@@ -12,6 +12,7 @@
 
 #define pr_fmt(fmt) "NMI watchdog: " fmt
 
+#include <linux/panic.h>
 #include <linux/nmi.h>
 #include <linux/atomic.h>
 #include <linux/module.h>
@@ -108,6 +109,9 @@ static void watchdog_overflow_callback(struct perf_event *event,
 	/* Ensure the watchdog never gets throttled */
 	event->hw.interrupts = 0;
 
+	if (panic_in_progress())
+		return;
+
 	if (!watchdog_check_timestamp())
 		return;
 
-- 
2.43.0