linux-kernel - Re: [PATCH 4/5] sh: ftrace: fix the comments for ftrace_modify

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Message-ID: <56618AAB.2000202@cogentembedded.com>
Date:	Fri, 4 Dec 2015 15:44:27 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Li Bin <huawei.libin@...wei.com>, rostedt@...dmis.org,
	mingo@...hat.com
Cc:	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org
Subject: Re: [PATCH 4/5] sh: ftrace: fix the comments for ftrace_modify_code

Hello.

On 12/4/2015 10:27 AM, 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: linux-sh@...r.kernel.org
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Li Bin <huawei.libin@...wei.com>
> ---
>   arch/sh/kernel/ftrace.c |   13 ++++++-------
>   1 files changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/arch/sh/kernel/ftrace.c b/arch/sh/kernel/ftrace.c
> index 079d70e..b696f92 100644
> --- a/arch/sh/kernel/ftrace.c
> +++ b/arch/sh/kernel/ftrace.c
> @@ -212,13 +212,12 @@ static int ftrace_modify_code(unsigned long ip, unsigned 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 were to happen, it

    s/were/was/.

[...]

MBR, Sergei

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