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[60.39.60.229]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2fceb065299sm157916a91.29.2025.02.20.18.23.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Feb 2025 18:23:54 -0800 (PST) From: Ryo Takakura To: hamzamahfooz@linux.microsoft.com Cc: akpm@linux-foundation.org, bhe@redhat.com, decui@microsoft.com, gregkh@linuxfoundation.org, haiyangz@microsoft.com, jani.nikula@intel.com, jfalempe@redhat.com, joel.granados@kernel.org, john.ogness@linutronix.de, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, pmladek@suse.com, takakura@valinux.co.jp, wei.liu@kernel.org Subject: Re: [PATCH RFC] panic: call panic handlers before panic_other_cpus_shutdown() Date: Fri, 21 Feb 2025 11:23:28 +0900 Message-Id: <20250221022328.47078-1-ryotkkr98@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250220225302.195282-1-hamzamahfooz@linux.microsoft.com> References: <20250220225302.195282-1-hamzamahfooz@linux.microsoft.com> Precedence: bulk X-Mailing-List: linux-hyperv@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hi Hamza! On Thu, 20 Feb 2025 17:53:00 -0500, Hamza Mahfooz wrote: >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 >--- > kernel/panic.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > >diff --git a/kernel/panic.c b/kernel/panic.c >index fbc59b3b64d0..9712a46dfe27 100644 >--- a/kernel/panic.c >+++ b/kernel/panic.c >@@ -372,8 +372,6 @@ 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(); I think printk_legacy_allow_panic_sync() is placed after panic_other_cpus_shutdown() so that it flushes the stored cpus backtraces as described [0]. > /* >@@ -382,6 +380,8 @@ void panic(const char *fmt, ...) > */ > atomic_notifier_call_chain(&panic_notifier_list, 0, buf); > >+ panic_other_cpus_shutdown(_crash_kexec_post_notifiers); >+ So maybe panic_other_cpus_shutdown() should be palced after atomic_notifier_call_chain() along with printk_legacy_allow_panic_sync() like below? ----- BEGIN ----- diff --git a/kernel/panic.c b/kernel/panic.c index d8635d5cecb2..7ac40e85ee27 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); ----- END ----- Sincerely, Ryo Takakura [0] https://lore.kernel.org/all/20240820063001.36405-30-john.ogness@linutronix.de/