on 2015/12/4 10:50, Steven Rostedt wrote:
> 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.
Ok, I will modify it.
Thanks,
Li Bin
> -- 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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