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

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Message-ID: <20241003183649.0290f0d1@gandalf.local.home>
Date: Thu, 3 Oct 2024 18:36:49 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
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 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.

-- Steve

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