+ panic-call-panic-handlers-before-panic_other_cpus_shutdown.patch added to mm-nonmm-unstable branch

+ panic-call-panic-handlers-before-panic_other_cpus_shutdown.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: panic: call panic handlers before panic_other_cpus_shutdown()
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     panic-call-panic-handlers-before-panic_other_cpus_shutdown.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/panic-call-panic-handlers-before-panic_other_cpus_shutdown.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Subject: panic: call panic handlers before panic_other_cpus_shutdown()
Date: Fri, 21 Feb 2025 16:30:52 -0500

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.

Link: https://lkml.kernel.org/r/20250221213055.133849-1-hamzamahfooz@linux.microsoft.com
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Baoquan he <bhe@redhat.com>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Ryo Takakura <takakura@valinux.co.jp>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/panic.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/kernel/panic.c~panic-call-panic-handlers-before-panic_other_cpus_shutdown
+++ a/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);
_

Patches currently in -mm which might be from hamzamahfooz@linux.microsoft.com are

panic-call-panic-handlers-before-panic_other_cpus_shutdown.patch

Re: + panic-call-panic-handlers-before-panic_other_cpus_shutdown.patch added to mm-nonmm-unstable branch

[Wei Liu]

Hi Andrew,

On Fri, Feb 21, 2025 at 04:00:08PM -0800, Andrew Morton wrote:
> 
> The patch titled
>      Subject: panic: call panic handlers before panic_other_cpus_shutdown()
> has been added to the -mm mm-nonmm-unstable branch.  Its filename is
>      panic-call-panic-handlers-before-panic_other_cpus_shutdown.patch
> 

Can you please hold off applying this patch? There is an active
discussion on the mailing list. I would like Hamza to answer the
questions there first.

Thanks,
Wei.