From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933254Ab1JZOeO (ORCPT ); Wed, 26 Oct 2011 10:34:14 -0400 Received: from mtagate3.uk.ibm.com ([194.196.100.163]:56321 "EHLO mtagate3.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932772Ab1JZOeN (ORCPT ); Wed, 26 Oct 2011 10:34:13 -0400 Message-ID: <1319639649.3321.11.camel@br98xy6r> Subject: [PATCH] kdump: Fix crash_kexec - smp_send_stop race in panic From: Michael Holzheu Reply-To: holzheu@linux.vnet.ibm.com To: akpm@linux-foundation.org Cc: "Eric W. Biederman" , Vivek Goyal , schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Date: Wed, 26 Oct 2011 16:34:09 +0200 Organization: IBM Content-Type: text/plain; charset="us-ascii" X-Mailer: Evolution 3.2.0- Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Andrew, After the discussion with Eric and Vivek the following patch seems to be a good solution to me. Could you accept this patch? When two CPUs call panic at the same time there is a possible race condition that can stop kdump. The first CPU calls crash_kexec() and the second CPU calls smp_send_stop() in panic() before crash_kexec() finished on the first CPU. So the second CPU stops the first CPU and therefore kdump fails: 1st CPU: panic()->crash_kexec()->mutex_trylock(&kexec_mutex)-> do kdump 2nd CPU: panic()->crash_kexec()->kexec_mutex already held by 1st CPU ->smp_send_stop()-> stop 1st CPU (stop kdump) This patch fixes the problem by introducing a spinlock in panic that allows only one CPU to process crash_kexec() and the subsequent panic code. Signed-off-by: Michael Holzheu --- kernel/panic.c | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/kernel/panic.c +++ b/kernel/panic.c @@ -59,6 +59,7 @@ EXPORT_SYMBOL(panic_blink); */ NORET_TYPE void panic(const char * fmt, ...) { + static DEFINE_SPINLOCK(panic_lock); static char buf[1024]; va_list args; long i, i_next = 0; @@ -82,6 +83,13 @@ NORET_TYPE void panic(const char * fmt, #endif /* + * Only one CPU is allowed to execute the panic code from here. For + * multiple parallel invocations of panic all other CPUs will wait on + * the panic_lock. They are stopped afterwards by smp_send_stop(). + */ + spin_lock(&panic_lock); + + /* * If we have crashed and we have a crash kernel loaded let it handle * everything else. * Do we want to call this before we try to display a message?