On Fri, 4 Dec 2015 10:18:39 +0800
Li Bin <huawei.li...@huawei.com> wrote:
> There is no need to worry about module 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.
>
> Signed-off-by: Li Bin <huawei.li...@huawei.com>
> ---
> arch/arm64/kernel/ftrace.c | 5 +----
> 1 files changed, 1 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> index 9669b33..ee91c0c 100644
> --- a/arch/arm64/kernel/ftrace.c
> +++ b/arch/arm64/kernel/ftrace.c
> @@ -29,12 +29,9 @@ static int ftrace_modify_code(unsigned long pc, u32 old,
> u32 new,
>
> /*
> * Note:
> - * Due to modules and __init, code can disappear and change,
> + * Due to __init, code can disappear and change,
Init code should not be modified either because it is black listed in
recordmcount.c.
I say just change the comment to be something like:
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.
-- Steve
> * we need to protect against faulting as well as code changing.
> * We do this by aarch64_insn_*() which use the probe_kernel_*().
> - *
> - * No lock is held here because all the modifications are run
> - * through stop_machine().
> */
> if (validate) {
> if (aarch64_insn_read((void *)pc, &replaced))
--
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