From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtprelay.hostedemail.com (smtprelay0230.hostedemail.com [216.40.44.230]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41E1C1A0907 for ; Thu, 24 Dec 2015 04:35:05 +1100 (AEDT) Date: Wed, 23 Dec 2015 12:34:59 -0500 From: Steven Rostedt To: Li Bin Cc: , , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Subject: Re: [PATCH v2 3/5] powerpc: ftrace: fix the comments for ftrace_modify_code Message-ID: <20151223123459.722b4a5c@gandalf.local.home> In-Reply-To: <1449367378-29430-4-git-send-email-huawei.libin@huawei.com> References: <1449367378-29430-1-git-send-email-huawei.libin@huawei.com> <1449367378-29430-4-git-send-email-huawei.libin@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, 6 Dec 2015 10:02:56 +0800 Li Bin wrote: > 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 Hi, can I get a POWERPC maintainer to ack this, or you can take it too. -- Steve > --- > arch/powerpc/kernel/ftrace.c | 12 +++++------- > 1 files changed, 5 insertions(+), 7 deletions(-) > > diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c > index 44d4d8e..83e3c88 100644 > --- a/arch/powerpc/kernel/ftrace.c > +++ b/arch/powerpc/kernel/ftrace.c > @@ -47,13 +47,11 @@ 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 was to happen, it > + * could cause us to read or write to someplace that could cause harm. > + * Carefully read and modify the code with 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 */