[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20250510074456.805a16872b591e2971a4d221@kernel.org>
Date: Sat, 10 May 2025 07:44:56 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: paulcacheux@...il.com
Cc: Paul Cacheux via B4 Relay <devnull+paulcacheux.gmail.com@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com>, Namhyung Kim <namhyung@...nel.org>,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] tracing: protect trace_probe_log with mutex
On Fri, 02 May 2025 15:15:53 +0200
Paul Cacheux via B4 Relay <devnull+paulcacheux.gmail.com@...nel.org> wrote:
> From: Paul Cacheux <paulcacheux@...il.com>
>
> The shared trace_probe_log variable can be accessed and modified
> by multiple processes using tracefs at the same time, this new
> mutex will guarantee it's always in a coherent state.
Actually that's not happen. For the create part (and currently the
event_log is used only in the creation), `dyn_event_ops_mutex` is already
held in create_dyn_event(). Thus, it is already serialized.
And even if there are multiple events are done in parallel, this
is not enough because trace_probe_log::argc/argv can be changed
before other user finishs to use the log.
Thank you,
>
> There is no guarantee that multiple errors happening at the same
> time will each have the correct error message, but at least this
> won't crash.
>
> Fixes: ab105a4fb894 ("tracing: Use tracing error_log with probe events")
>
> Signed-off-by: Paul Cacheux <paulcacheux@...il.com>
> ---
> kernel/trace/trace_probe.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 2eeecb6c95eea55502b83af6775b7b6f0cc5ab94..14a7a0b59cd20a8bc43e3e7c653e986081f924c8 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -154,9 +154,11 @@ static const struct fetch_type *find_fetch_type(const char *type, unsigned long
> }
>
> static struct trace_probe_log trace_probe_log;
> +static DEFINE_MUTEX(trace_probe_log_lock);
>
> void trace_probe_log_init(const char *subsystem, int argc, const char **argv)
> {
> + guard(mutex)(&trace_probe_log_lock);
> trace_probe_log.subsystem = subsystem;
> trace_probe_log.argc = argc;
> trace_probe_log.argv = argv;
> @@ -165,11 +167,13 @@ void trace_probe_log_init(const char *subsystem, int argc, const char **argv)
>
> void trace_probe_log_clear(void)
> {
> + guard(mutex)(&trace_probe_log_lock);
> memset(&trace_probe_log, 0, sizeof(trace_probe_log));
> }
>
> void trace_probe_log_set_index(int index)
> {
> + guard(mutex)(&trace_probe_log_lock);
> trace_probe_log.index = index;
> }
>
> @@ -178,6 +182,8 @@ void __trace_probe_log_err(int offset, int err_type)
> char *command, *p;
> int i, len = 0, pos = 0;
>
> + guard(mutex)(&trace_probe_log_lock);
> +
> if (!trace_probe_log.argv)
> return;
>
>
> --
> 2.49.0
>
>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
Powered by blists - more mailing lists