On 2021/10/12 下午8:29, Steven Rostedt wrote:
> On Tue, 12 Oct 2021 14:24:43 +0200 (CEST)
> Miroslav Benes <mbe...@suse.cz> wrote:
>
>>> +++ b/kernel/livepatch/patch.c
>>> @@ -52,11 +52,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>>> bit = ftrace_test_recursion_trylock(ip, parent_ip);
>>> if (WARN_ON_ONCE(bit < 0))
>>> return;
>>> - /*
>>> - * A variant of synchronize_rcu() is used to allow patching functions
>>> - * where RCU is not watching, see klp_synchronize_transition().
>>> - */
>>> - preempt_disable_notrace();
>>>
>>> func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
>>> stack_node);
>>> @@ -120,7 +115,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>>> klp_arch_set_pc(fregs, (unsigned long)func->new_func);
>>>
>>> unlock:
>>> - preempt_enable_notrace();
>>> ftrace_test_recursion_unlock(bit);
>>> }
>>
>> I don't like this change much. We have preempt_disable there not because
>> of ftrace_test_recursion, but because of RCU. ftrace_test_recursion was
>> added later. Yes, it would work with the change, but it would also hide
>> things which should not be hidden in my opinion.
>
> Agreed, but I believe the change is fine, but requires a nice comment to
> explain what you said above.
>
> Thus, before the "ftrace_test_recursion_trylock()" we need:
>
> /*
> * The ftrace_test_recursion_trylock() will disable preemption,
> * which is required for the variant of synchronize_rcu() that is
> * used to allow patching functions where RCU is not watching.
> * See klp_synchronize_transition() for more details.
> */
Will be in v2 too :-)
Regards,
Michael Wang
>
> -- Steve
>
