linux-kernel - [PATCH v13 02/12] tracing/probes: Avoid setting TPARG_FL_FENTRY and TPARG_FL

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Date:   Fri, 26 May 2023 12:18:07 +0800
From:   "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To:     linux-trace-kernel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        mhiramat@...nel.org, Florent Revest <revest@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>, bpf@...r.kernel.org,
        Bagas Sanjaya <bagasdotme@...il.com>
Subject: [PATCH v13 02/12] tracing/probes: Avoid setting TPARG_FL_FENTRY and TPARG_FL_RETURN

From: Masami Hiramatsu (Google) <mhiramat@...nel.org>

When parsing a kprobe event, the return probe always sets both
TPARG_FL_RETURN and TPARG_FL_FENTRY, but this is not useful because
some fetchargs are only for return probe and some others only for
function entry. Make it obviously mutual exclusive.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
---
 kernel/trace/trace_kprobe.c |    2 +-
 kernel/trace/trace_probe.h  |    5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 59cda19a9033..867ffb7ee31d 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -825,7 +825,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 		if (is_return)
 			flags |= TPARG_FL_RETURN;
 		ret = kprobe_on_func_entry(NULL, symbol, offset);
-		if (ret == 0)
+		if (ret == 0 && !is_return)
 			flags |= TPARG_FL_FENTRY;
 		/* Defer the ENOENT case until register kprobe */
 		if (ret == -EINVAL && is_return) {
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index ef8ed3b65d05..752a08fcf0be 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -357,6 +357,11 @@ int trace_probe_print_args(struct trace_seq *s, struct probe_arg *args, int nr_a
 #define trace_probe_for_each_link_rcu(pos, tp)	\
 	list_for_each_entry_rcu(pos, &(tp)->event->files, list)
 
+/*
+ * The flags used for parsing trace_probe arguments.
+ * TPARG_FL_RETURN, TPARG_FL_FENTRY and TPARG_FL_TPOINT are mutually exclusive.
+ * TPARG_FL_KERNEL and TPARG_FL_USER are also mutually exclusive.
+ */
 #define TPARG_FL_RETURN BIT(0)
 #define TPARG_FL_KERNEL BIT(1)
 #define TPARG_FL_FENTRY BIT(2)