linux-kernel - Re: [PATCH 4/8] tracing/bpf: guard syscall probe with preempt

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Message-ID: <CAEf4BzZUgLaK8r5VK4VmfQTEKZ13qDEGUEEdeKJeZYc_96KCTw@mail.gmail.com>
Date: Mon, 9 Sep 2024 17:03:02 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, 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>, 
	bpf@...r.kernel.org, Joel Fernandes <joel@...lfernandes.org>, 
	linux-trace-kernel@...r.kernel.org, Michael Jeanson <mjeanson@...icios.com>
Subject: Re: [PATCH 4/8] tracing/bpf: guard syscall probe with preempt_notrace

On Mon, Sep 9, 2024 at 1:17 PM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> In preparation for allowing system call enter/exit instrumentation to
> handle page faults, make sure that bpf can handle this change by
> explicitly disabling preemption within the bpf system call tracepoint
> probes to respect the current expectations within bpf tracing code.
>
> This change does not yet allow bpf to take page faults per se within its
> probe, but allows its existing probes to adapt to the upcoming change.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Michael Jeanson <mjeanson@...icios.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Yonghong Song <yhs@...com>
> Cc: Paul E. McKenney <paulmck@...nel.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Cc: bpf@...r.kernel.org
> Cc: Joel Fernandes <joel@...lfernandes.org>
> ---
>  include/trace/bpf_probe.h | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>

LGTM.

Acked-by: Andrii Nakryiko <andrii@...nel.org>


> diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h
> index c85bbce5aaa5..211b98d45fc6 100644
> --- a/include/trace/bpf_probe.h
> +++ b/include/trace/bpf_probe.h
> @@ -53,8 +53,17 @@ __bpf_trace_##call(void *__data, proto)                                      \
>  #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
>         __BPF_DECLARE_TRACE(call, PARAMS(proto), PARAMS(args))
>
> +#define __BPF_DECLARE_TRACE_SYSCALL(call, proto, args)                 \
> +static notrace void                                                    \
> +__bpf_trace_##call(void *__data, proto)                                        \
> +{                                                                      \
> +       guard(preempt_notrace)();                                       \
> +       CONCATENATE(bpf_trace_run, COUNT_ARGS(args))(__data, CAST_TO_U64(args));        \
> +}
> +
>  #undef DECLARE_EVENT_SYSCALL_CLASS
> -#define DECLARE_EVENT_SYSCALL_CLASS DECLARE_EVENT_CLASS
> +#define DECLARE_EVENT_SYSCALL_CLASS(call, proto, args, tstruct, assign, print) \
> +       __BPF_DECLARE_TRACE_SYSCALL(call, PARAMS(proto), PARAMS(args))
>
>  /*
>   * This part is compiled out, it is only here as a build time check
> --
> 2.39.2
>