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

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Message-ID: <87cyjk2kgg.ffs@tglx>
Date: Mon, 28 Oct 2024 18:42:07 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Steven Rostedt
 <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>
Cc: linux-kernel@...r.kernel.org, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, 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 resend 6/8] tracing/ftrace: Add might_fault check to
 syscall probes

On Mon, Sep 30 2024 at 15:23, Mathieu Desnoyers wrote:
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index a3d8ac00793e..0430890cbb42 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -303,6 +303,7 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
>  	 * Syscall probe called with preemption enabled, but the ring
>  	 * buffer and per-cpu data require preemption to be disabled.
>  	 */
> +	might_fault();
>  	guard(preempt_notrace)();

I find it odd that the might_fault() check is in all the implementations
and not in the tracepoint itself:

    if (syscall) {
        might_fault();
 	rcu_read_unlock_trace();
   } else ...     

That's where I would have expected it to be.

Thanks,

        tglx