Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758145AbZCPMzm (ORCPT ); Mon, 16 Mar 2009 08:55:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752608AbZCPMzb (ORCPT ); Mon, 16 Mar 2009 08:55:31 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:55747 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1757340AbZCPMzb (ORCPT ); Mon, 16 Mar 2009 08:55:31 -0400 Message-ID: <49BE4BF7.6050407@cn.fujitsu.com> Date: Mon, 16 Mar 2009 20:54:15 +0800 From: Lai Jiangshan User-Agent: Thunderbird 2.0.0.6 (Windows/20070728) MIME-Version: 1.0 To: Ingo Molnar , Steven Rostedt , LKML Subject: [PATCH] ftrace: protect executing nmi Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2867 Lines: 73 When I review the sensitive code ftrace_nmi_enter(), I found the atomic variable nmi_running does protect NMI VS do_ftrace_mod_code(), but it can not protects NMI(entered nmi) VS NMI(ftrace_nmi_enter()). cpu#1 | cpu#2 | cpu#3 ftrace_nmi_enter() | do_ftrace_mod_code() | not modify | | ------------------------|-----------------------|-- executing | set mod_code_write = 1| executing --|-----------------------|-------------------- executing | | ftrace_nmi_enter() executing | | do modify ------------------------|-----------------------|----------------- ftrace_nmi_exit() | | cpu#3 may be being modified the code which is still being executed on cpu#1, it will have undefined results and possibly take a GPF, this patch prevents it occurred. Signed-off-by: Lai Jiangshan --- diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 1d0d7f4..e016f5e 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -87,7 +87,8 @@ static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) * * If an NMI is executed, the first thing it does is to call * "ftrace_nmi_enter". This will check if the flag is set to write - * and if it is, it will write what is in the IP and "code" buffers. + * and if it is, and there is no executing nmi, it will write + * what is in the IP and "code" buffers. * * The trick is, it does not matter if everyone is writing the same * content to the code location. Also, if a CPU is executing code @@ -96,6 +97,7 @@ static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr) */ static atomic_t nmi_running = ATOMIC_INIT(0); +static atomic_t nmi_executing = ATOMIC_INIT(0); static int mod_code_status; /* holds return value of text write */ static int mod_code_write; /* set when NMI should do the write */ static void *mod_code_ip; /* holds the IP to write to */ @@ -135,14 +137,18 @@ void ftrace_nmi_enter(void) atomic_inc(&nmi_running); /* Must have nmi_running seen before reading write flag */ smp_mb(); - if (mod_code_write) { + if (!atomic_read(&nmi_executing) && mod_code_write) { ftrace_mod_code(); atomic_inc(&nmi_update_count); } + atomic_inc(&nmi_executing); + smp_mb(); } void ftrace_nmi_exit(void) { + smp_mb(); + atomic_dec(&nmi_executing); /* Finish all executions before clearing nmi_running */ smp_wmb(); atomic_dec(&nmi_running); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/