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SubjectRe: [PATCH v2 2/5] metag: ftrace: fix the comments for ftrace_modify_code
On Sun, 6 Dec 2015 10:02:55 +0800
Li Bin <huawei.libin@huawei.com> 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: James Hogan <james.hogan@imgtec.com>
> Cc: linux-metag@vger.kernel.org
> Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Li Bin <huawei.libin@huawei.com>

Hi, can I get a metag maintainer to ack this. Or you can take the patch
too.

-- Steve

> ---
> arch/metag/kernel/ftrace.c | 11 +++++------
> 1 files changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/arch/metag/kernel/ftrace.c b/arch/metag/kernel/ftrace.c
> index ed1d685..ac8c039 100644
> --- a/arch/metag/kernel/ftrace.c
> +++ b/arch/metag/kernel/ftrace.c
> @@ -54,12 +54,11 @@ static int ftrace_modify_code(unsigned long pc, 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.
> - *
> - * No real locking needed, this code is run through
> - * kstop_machine.
> + * 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 */



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