From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932308AbcH3H6b (ORCPT ); Tue, 30 Aug 2016 03:58:31 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:33739 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755700AbcH3H61 (ORCPT ); Tue, 30 Aug 2016 03:58:27 -0400 Date: Tue, 30 Aug 2016 16:58:34 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: Sergey Senozhatsky , Andrew Morton , Jan Kara , linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: Re: [PATCH] printk/nmi: avoid direct printk()-s from __printk_nmi_flush() Message-ID: <20160830075834.GA494@swordfish> References: <20160829123220.1295-1-sergey.senozhatsky@gmail.com> <20160829151600.GM4866@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160829151600.GM4866@pathway.suse.cz> User-Agent: Mutt/1.7.0 (2016-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Petr, one more question. Not related to the patch, but still related to NMI. can NMI nest? CPU0 -> NMI#0 printk_nmi_enter() this_cpu_write(printk_func, vprintk_nmi) ... => NMI#1 : printk_nmi_enter() : this_cpu_write(printk_func, vprintk_nmi) : this_cpu_read(printk_func)(fmt, args) : ^^^^^^^^^^^^^ OK, vprintk_nmi() from NMI : printk_nmi_exit() : this_cpu_write(printk_func, vprintk_default) << return NMI#1 this_cpu_read(printk_func)(fmt, args) ^^^^^^^^^^^^^ vprintk_default() from NMI? printk_nmi_exit() this_cpu_write(printk_func, vprintk_default) return NMI#0 can this happen? shouldn't we do something like this then? /* not tested */ Signed-off-by: Sergey Senozhatsky --- kernel/printk/internal.h | 2 ++ kernel/printk/nmi.c | 9 ++++++++- 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 7fd2838..5b7508f 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -31,6 +31,8 @@ extern raw_spinlock_t logbuf_lock; * via per-CPU variable. */ DECLARE_PER_CPU(printk_func_t, printk_func); +DECLARE_PER_CPU(printk_func_t, printk_func_saved); + static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return this_cpu_read(printk_func)(fmt, args); diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c index 16bab47..9d83929 100644 --- a/kernel/printk/nmi.c +++ b/kernel/printk/nmi.c @@ -39,6 +39,7 @@ * were handled or when IRQs are blocked. */ DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default; +DEFINE_PER_CPU(printk_func_t, printk_func_saved); static int printk_nmi_irq_ready; atomic_t nmi_message_lost; @@ -259,10 +260,16 @@ void __init printk_nmi_init(void) void printk_nmi_enter(void) { + printk_func_t func = this_cpu_read(printk_func); + + if (func != vprintk_nmi) + this_cpu_write(printk_func_saved, func); this_cpu_write(printk_func, vprintk_nmi); } void printk_nmi_exit(void) { - this_cpu_write(printk_func, vprintk_default); + printk_func_t func = this_cpu_read(printk_func_saved); + + this_cpu_write(printk_func, func); } -- 2.9.3