linux-kernel - Re: [PATCH v1 6/8] tracing/ftrace: Add might

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Message-ID: <a5c1160f-79a4-42ba-97b9-bb7f10ffcb21@efficios.com>
Date: Thu, 3 Oct 2024 20:11:06 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, linux-kernel@...r.kernel.org,
 Peter Zijlstra <peterz@...radead.org>, Alexei Starovoitov <ast@...nel.org>,
 Yonghong Song <yhs@...com>, "Paul E . McKenney" <paulmck@...nel.org>,
 Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Namhyung Kim <namhyung@...nel.org>,
 Andrii Nakryiko <andrii.nakryiko@...il.com>, bpf@...r.kernel.org,
 Joel Fernandes <joel@...lfernandes.org>, linux-trace-kernel@...r.kernel.org,
 Michael Jeanson <mjeanson@...icios.com>
Subject: Re: [PATCH v1 6/8] tracing/ftrace: Add might_fault check to syscall
 probes

On 2024-10-04 00:36, Steven Rostedt wrote:
> On Thu,  3 Oct 2024 11:16:36 -0400
> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> 
>> diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
>> index 0228d9ed94a3..e0d4850b0d77 100644
>> --- a/include/trace/trace_events.h
>> +++ b/include/trace/trace_events.h
>> @@ -446,6 +446,7 @@ __DECLARE_EVENT_CLASS(call, PARAMS(proto), PARAMS(args), PARAMS(tstruct), \
>>   static notrace void							\
>>   trace_event_raw_event_##call(void *__data, proto)			\
>>   {									\
>> +	might_fault();							\
> 
> I don't think we want "might_fault()" here, as this is called for every
> tracepoint that is created by the TRACE_EVENT() macro. That means, there's
> going to be plenty of locations this gets called at that do not allow faults.

Here is the full context where this line applies:

#undef DECLARE_EVENT_SYSCALL_CLASS
#define DECLARE_EVENT_SYSCALL_CLASS(call, proto, args, tstruct, assign, print) \
__DECLARE_EVENT_CLASS(call, PARAMS(proto), PARAMS(args), PARAMS(tstruct), \
                       PARAMS(assign), PARAMS(print))                    \
static notrace void                                                     \
trace_event_raw_event_##call(void *__data, proto)                       \
{                                                                       \
         might_fault();                                                  \
         guard(preempt_notrace)();                                       \
         do_trace_event_raw_event_##call(__data, args);                  \
}

Not an issue, since it's only for syscall tracepoints.

Thanks,

Mathieu

> 
> -- Steve
> 
> 
>>   	guard(preempt_notrace)();					\
>>   	do_trace_event_raw_event_##call(__data, args);			\
>>   }

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com