Thread (5 messages) 5 messages, 2 authors, 2025-01-29

Re: [PATCH v3 25/28] bpf: Use RCU in all users of __module_text_address().

From: Alexei Starovoitov <hidden>
Date: 2025-01-09 18:38:15
Also in: bpf, linux-modules, lkml

On Wed, Jan 8, 2025 at 1:05 AM Sebastian Andrzej Siewior
[off-list ref] wrote:
quoted hunk ↗ jump to hunk
__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@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Hao Luo <redacted>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Matt Bobrowski <mattbobrowski@google.com>
Cc: Song Liu <song@kernel.org>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: bpf@vger.kernel.org
Cc: linux-trace-kernel@vger.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/trace/bpf_trace.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 1b8db5aee9d38..020df7b6ff90c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2336,10 +2336,9 @@ 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
@@ -2907,16 +2906,14 @@ static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u3
        for (i = 0; i < addrs_cnt; i++) {
                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 we it's already stored  */
+                       if (!mod || has_module(&arr, mod))
+                               continue;
+                       if (!try_module_get(mod))
+                               err = -EINVAL;
lgtm.
Should we take into bpf-next or the whole set is handled together
somewhere?
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