linux-kernel - [PATCH v2] panic: call panic handlers before panic_other_cpus

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Message-ID: <20250221213055.133849-1-hamzamahfooz@linux.microsoft.com>
Date: Fri, 21 Feb 2025 16:30:52 -0500
From: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>
To: linux-kernel@...r.kernel.org
Cc: Dexuan Cui <decui@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>,
	linux-hyperv@...r.kernel.org,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>,
	Petr Mladek <pmladek@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	John Ogness <john.ogness@...utronix.de>,
	Jani Nikula <jani.nikula@...el.com>,
	Baoquan He <bhe@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ryo Takakura <takakura@...inux.co.jp>
Subject: [PATCH v2] panic: call panic handlers before panic_other_cpus_shutdown()

Since, the panic handlers may require certain cpus to be online to panic
gracefully, we should call them before turning off SMP. Without this
re-ordering, on Hyper-V hv_panic_vmbus_unload() times out, because the
vmbus channel is bound to VMBUS_CONNECT_CPU and unless the crashing cpu
is the same as VMBUS_CONNECT_CPU, VMBUS_CONNECT_CPU will be offlined by
crash_smp_send_stop() before the vmbus channel can be deconstructed.

Signed-off-by: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>
---
v2: keep printk_legacy_allow_panic_sync() after
    panic_other_cpus_shutdown().
---
 kernel/panic.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/panic.c b/kernel/panic.c
index fbc59b3b64d0..433cf651e213 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -372,16 +372,16 @@ void panic(const char *fmt, ...)
 	if (!_crash_kexec_post_notifiers)
 		__crash_kexec(NULL);
 
-	panic_other_cpus_shutdown(_crash_kexec_post_notifiers);
-
-	printk_legacy_allow_panic_sync();
-
 	/*
 	 * Run any panic handlers, including those that might need to
 	 * add information to the kmsg dump output.
 	 */
 	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
 
+	panic_other_cpus_shutdown(_crash_kexec_post_notifiers);
+
+	printk_legacy_allow_panic_sync();
+
 	panic_print_sys_info(false);
 
 	kmsg_dump_desc(KMSG_DUMP_PANIC, buf);
-- 
2.47.1