Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755229AbbLDHby (ORCPT ); Fri, 4 Dec 2015 02:31:54 -0500 Received: from szxga03-in.huawei.com ([119.145.14.66]:21721 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751973AbbLDHbw (ORCPT ); Fri, 4 Dec 2015 02:31:52 -0500 From: Li Bin To: , CC: , Li Bin , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Subject: [PATCH 3/5] powerpc: ftrace: fix the comments for ftrace_modify_code Date: Fri, 4 Dec 2015 15:27:45 +0800 Message-ID: <1449214067-12177-4-git-send-email-huawei.libin@huawei.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1449214067-12177-1-git-send-email-huawei.libin@huawei.com> References: <1449214067-12177-1-git-send-email-huawei.libin@huawei.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.175.100.166] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020203.5661408F.0100,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-05-26 15:14:31, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 9c8aea2b9eac958e27dded4bf061b9a1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2202 Lines: 53 There is no need to worry about module and __init text disappearing case, because that ftrace has a module notifier that is called when a module is being unloaded and before the text goes away and this code grabs the ftrace_lock mutex and removes the module functions from the ftrace list, such that it will no longer do any modifications to that module's text, the update to make functions be traced or not is done under the ftrace_lock mutex as well. And by now, __init section codes should not been modified by ftrace, because it is black listed in recordmcount.c and ignored by ftrace. Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Michael Ellerman Cc: linuxppc-dev@lists.ozlabs.org Suggested-by: Steven Rostedt Signed-off-by: Li Bin --- arch/powerpc/kernel/ftrace.c | 13 ++++++------- 1 files changed, 6 insertions(+), 7 deletions(-) diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c index 44d4d8e..c6452b2 100644 --- a/arch/powerpc/kernel/ftrace.c +++ b/arch/powerpc/kernel/ftrace.c @@ -47,13 +47,12 @@ ftrace_modify_code(unsigned long ip, unsigned int old, unsigned int new) unsigned int replaced; /* - * Note: Due to modules and __init, code can - * disappear and change, we need to protect against faulting - * as well as code changing. We do this by using the - * probe_kernel_* functions. - * - * No real locking needed, this code is run through - * kstop_machine, or before SMP starts. + * Note: + * We are paranoid about modifying text, as if a bug were to happen, it + * could cause us to read or write to someplace that could cause harm. + * Carefully read and modify the code with aarch64_insn_*() which uses + * probe_kernel_*(), and make sure what we read is what we expected it + * to be before modifying it. */ /* read the text we want to modify */ -- 1.7.1 -- 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/