linux-kernel - [PATCH v3.5 25/28] bpf: Use RCU in all users of __module_text

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Message-ID: <20250129084751.tH6iidUO@linutronix.de>
Date: Wed, 29 Jan 2025 09:47:51 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: linux-modules@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Daniel Gomez <da.gomez@...sung.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Eduard Zingerman <eddyz87@...il.com>, Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Matt Bobrowski <mattbobrowski@...gle.com>,
	Song Liu <song@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Steven Rostedt <rostedt@...dmis.org>,
	Yonghong Song <yonghong.song@...ux.dev>, bpf <bpf@...r.kernel.org>,
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>
Subject: [PATCH v3.5 25/28] bpf: Use RCU in all users of
 __module_text_address().

__module_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_address() with
RCU.

Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Eduard Zingerman <eddyz87@...il.com>
Cc: Hao Luo <haoluo@...gle.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: John Fastabend <john.fastabend@...il.com>
Cc: KP Singh <kpsingh@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Matt Bobrowski <mattbobrowski@...gle.com>
Cc: Song Liu <song@...nel.org>
Cc: Stanislav Fomichev <sdf@...ichev.me>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Yonghong Song <yonghong.song@...ux.dev>
Cc: bpf@...r.kernel.org
Cc: linux-trace-kernel@...r.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---

The previous version was broken in terms that the break statement broke
out of the scoped_guard loop and added something to the list. This is
now fixed by adding the "skip_add" bool.
While at it, I updated the comment by removing the "we".

 kernel/trace/bpf_trace.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index adc947587eb81..e6a17a60d8787 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2345,10 +2345,9 @@ void bpf_put_raw_tracepoint(struct bpf_raw_event_map *btp)
 {
 	struct module *mod;
 
-	preempt_disable();
+	guard(rcu)();
 	mod = __module_address((unsigned long)btp);
 	module_put(mod);
-	preempt_enable();
 }
 
 static __always_inline
@@ -2932,18 +2931,21 @@ static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u3
 	u32 i, err = 0;
 
 	for (i = 0; i < addrs_cnt; i++) {
+		bool skip_add = false;
 		struct module *mod;
 
-		preempt_disable();
-		mod = __module_address(addrs[i]);
-		/* Either no module or we it's already stored  */
-		if (!mod || has_module(&arr, mod)) {
-			preempt_enable();
-			continue;
+		scoped_guard(rcu) {
+			mod = __module_address(addrs[i]);
+			/* Either no module or it's already stored  */
+			if (!mod || has_module(&arr, mod)) {
+				skip_add = true;
+				break; /* scoped_guard */
+			}
+			if (!try_module_get(mod))
+				err = -EINVAL;
 		}
-		if (!try_module_get(mod))
-			err = -EINVAL;
-		preempt_enable();
+		if (skip_add)
+			continue;
 		if (err)
 			break;
 		err = add_module(&arr, mod);
-- 
2.47.2