linux-kernel - Re: [PATCH v2 5/5] x86: ftrace: fix the comments for ftrace_modify_code

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Date:	Tue, 29 Dec 2015 14:35:35 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Li Bin <huawei.libin@...wei.com>, mingo@...hat.com,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org
Subject: Re: [PATCH v2 5/5] x86: ftrace: fix the comments for
 ftrace_modify_code_direct

On Wed, 23 Dec 2015, Steven Rostedt wrote:
> On Sun, 6 Dec 2015 10:02:58 +0800
> Li Bin <huawei.libin@...wei.com> wrote:
> > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> > index 311bcf3..db0f6b1 100644
> > --- a/arch/x86/kernel/ftrace.c
> > +++ b/arch/x86/kernel/ftrace.c
> > @@ -106,13 +106,11 @@ ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
> >  	unsigned char replaced[MCOUNT_INSN_SIZE];
> >  
> >  	/*
> > -	 * 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.
> >  	 */
> 
> Thomas,
> 
> This has been now fixed. You want to ack it and I take it, or can you
> take it. Or is there something else that should be fixed?

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
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