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Subject: Re: [RESEND PATCH v2] trace: prevent preemption in
 perf_ftrace_function_call()
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        open list <linux-kernel@vger.kernel.org>,
        Jiri Olsa <jolsa@redhat.com>
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Date:   Mon, 11 Oct 2021 17:39:32 +0800
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On 2021/10/11 下午4:48, Peter Zijlstra wrote:
> On Mon, Oct 11, 2021 at 10:32:46AM +0200, Peter Zijlstra wrote:
>> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
>> index a9f9c5714e65..ca12e2d8e060 100644
>> --- a/include/linux/trace_recursion.h
>> +++ b/include/linux/trace_recursion.h
>> @@ -214,7 +214,14 @@ static __always_inline void trace_clear_recursion(int bit)
>>  static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
>>  							 unsigned long parent_ip)
>>  {
>> -	return trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START, TRACE_FTRACE_MAX);
>> +	bool ret;
>> +
>> +	preempt_disable_notrace();
>> +	ret = trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START, TRACE_FTRACE_MAX);
>> +	if (!ret)
>> +		preempt_enable_notrace();
>> +
>> +	return ret;
>>  }
>>  
>>  /**
> 
> Oh, I might've gotten that wrong, I assumed regular trylock semantics,
> but it doesn't look like that's right.

I will use bit instead ret and give some testing :-)

BTW, would you prefer to merge these changes into this patch or maybe send
another patch with your suggested-by?

Regards,
Michael Wang

>