From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423328AbcB0CVp (ORCPT ); Fri, 26 Feb 2016 21:21:45 -0500 Received: from mail-pf0-f178.google.com ([209.85.192.178]:34601 "EHLO mail-pf0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755905AbcB0CVn (ORCPT ); Fri, 26 Feb 2016 21:21:43 -0500 Date: Sat, 27 Feb 2016 11:19:44 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: Sergey Senozhatsky , Andrew Morton , Jan Kara , Peter Zijlstra , Steven Rostedt , Ingo Molnar , linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: Re: [PATCH] printk/nmi: restore printk_func in nmi_panic Message-ID: <20160227021944.GA1621@swordfish> References: <1456457840-1059-1-git-send-email-sergey.senozhatsky@gmail.com> <20160226145717.GZ12548@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160226145717.GZ12548@pathway.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Petr, On (02/26/16 15:57), Petr Mladek wrote: > On Fri 2016-02-26 12:37:20, Sergey Senozhatsky wrote: > > When watchdog detects a hardlockup and calls nmi_panic() `printk_func' > > must be restored via printk_nmi_exit() call, so panic() will be able > > to flush nmi buf and show backtrace and panic message. We also better > > explicitly ask nmi to printk_nmi_flush() in console_flush_on_panic(), > > because it may be too late to rely on irq work. > > > > Signed-off-by: Sergey Senozhatsky > > --- > > include/linux/kernel.h | 6 ++++-- > > kernel/printk/printk.c | 1 + > > 2 files changed, 5 insertions(+), 2 deletions(-) > > > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > > index f4fa2b2..3ee33d5 100644 > > --- a/include/linux/kernel.h > > +++ b/include/linux/kernel.h > > @@ -469,10 +469,12 @@ do { \ > > cpu = raw_smp_processor_id(); \ > > old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu); \ > > \ > > - if (old_cpu == PANIC_CPU_INVALID) \ > > + if (old_cpu == PANIC_CPU_INVALID) { \ > > + printk_nmi_exit(); \ > > This might end up in a deadlock that printk_nmi() wanted to avoid. aha, I see. > I think about a compromise. We should try to get the messages > out only when kdump is not enabled. can we zap_locks() if we are on nmi_panic()->panic()->console_flush_on_panic() path? console_flush_on_panic() is happening after we send out smp_send_stop(). > PS: I am sorry for not responding much about the printk problems > this week. I have attended a training and did not have much time > for a real work. no prob. -ss