linux-kernel - [PATCH bpf] bpf: trace: send signals asynchronously if !preemptible

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Message-Id: <20250115103647.38487-1-puranjay@kernel.org>
Date: Wed, 15 Jan 2025 10:36:47 +0000
From: Puranjay Mohan <puranjay@...nel.org>
To: Song Liu <song@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	KP Singh <kpsingh@...nel.org>,
	Matt Bobrowski <mattbobrowski@...gle.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	puranjay12@...il.com
Subject: [PATCH bpf] bpf: trace: send signals asynchronously if !preemptible

BPF programs can execute in all kinds of contexts and when a program
running in a non-preemptible context uses the bpf_send_signal() kfunc,
it will cause issues because this kfunc can sleep.

So change `irqs_disabled()` to `!preemptible()` that covers all edge
cases: preempt_count() == 0 and irqs_disabled()

Reported-by: syzbot+97da3d7e0112d59971de@...kaller.appspotmail.com
Closes: https://lore.kernel.org/all/67486b09.050a0220.253251.0084.GAE@google.com/
Fixes: 1bc7896e9ef4 ("bpf: Fix deadlock with rq_lock in bpf_send_signal()")
Signed-off-by: Puranjay Mohan <puranjay@...nel.org>
---
 kernel/trace/bpf_trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 1b8db5aee9d3..d162c87e09a8 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -853,7 +853,7 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type, struct task_struc
 	if (unlikely(is_global_init(task)))
 		return -EPERM;
 
-	if (irqs_disabled()) {
+	if (!preemptible()) {
 		/* Do an early check on signal validity. Otherwise,
 		 * the error is lost in deferred irq_work.
 		 */
-- 
2.40.1