Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked

王贇
2021-10-26T09:48:25Z

Hi, Miroslav

On 2021/10/26 下午5:35, Miroslav Benes wrote:
> Hi,
>
>> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
>> index abe1a50..2bc1522 100644
>> --- a/include/linux/trace_recursion.h
>> +++ b/include/linux/trace_recursion.h
>> @@ -135,6 +135,9 @@ static __always_inline int trace_get_context_bit(void)
>> # define do_ftrace_record_recursion(ip, pip) do { } while (0)
>> #endif
>>
>> +/*
>> + * Preemption is promised to be disabled when return bit > 0.
>> + */
>> static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip,
>> int start)
>> {
>> @@ -162,11 +165,17 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign
>> current->trace_recursion = val;
>> barrier();
>>
>> + preempt_disable_notrace();
>> +
>> return bit;
>> }
>>
>> +/*
>> + * Preemption will be enabled (if it was previously enabled).
>> + */
>> static __always_inline void trace_clear_recursion(int bit)
>> {
>> + preempt_enable_notrace();
>> barrier();
>> trace_recursion_clear(bit);
>> }
>
> The two comments should be updated too since Steven removed the "bit == 0"
> trick.

Could you please give more hint on how will it be correct?

I get the point that bit will no longer be 0, there are only -1 or > 0 now
so trace_test_and_set_recursion() will disable preemption on bit > 0 and
trace_clear_recursion() will enabled it since it should only be called when
bit > 0 (I remember we could use a WARN_ON here now :-P).

>
>> @@ -178,7 +187,7 @@ static __always_inline void trace_clear_recursion(int bit)
>> * tracing recursed in the same context (normal vs interrupt),
>> *
>> * Returns: -1 if a recursion happened.
>> - * >= 0 if no recursion
>> + * > 0 if no recursion.
>> */
>> static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
>> unsigned long parent_ip)
>
> And this change would not be correct now.

I thought it will no longer return 0 so I change it to > 0, isn't that correct?

Regards,
Michael Wang

>
> Regards
> Miroslav
>