# Re: \[PATCH v3 1/2\] ftrace: disable preemption between ftrace\_test\_recursion\_trylock/unlock()

- From: 王贇 \<hidden\>
- Date: 2021-10-14 09:22:54 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/10/1541642
- Thread: https://ratatoskr.run/linuxppc-dev/2021/10/1540082/t.md

```text


On 2021/10/14 下午5:13, Miroslav Benes wrote:
>> diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
>> index e8029ae..b8d75fb 100644
>> --- a/kernel/livepatch/patch.c
>> +++ b/kernel/livepatch/patch.c
>> @@ -49,14 +49,16 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>>
>>  	ops = container_of(fops, struct klp_ops, fops);
>>
>> +	/*
>> +	 *
> 
> This empty line is not useful.
> 
>> +	 * 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.
>> +	 */
>>  	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 +122,6 @@ 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);
>>  }
> 
> Acked-by: Miroslav Benes <mbenes@suse.cz>
> 
> for the livepatch part of the patch.
> 
> I would also ask you not to submit new versions so often, so that the 
> other reviewers have time to actually review the patch set.
> 
> Quoting from Documentation/process/submitting-patches.rst:
> 
> "Wait for a minimum of one week before resubmitting or pinging reviewers - 
> possibly longer during busy times like merge windows."

Thanks for the Ack and suggestion, will take care from now on :-)

Regards,
Michael Wang

> 
> Thanks
> 
> Miroslav
> 
```