1 files changed, 70 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/progs/timer_start_deadlock.c b/tools/testing/selftests/bpf/progs/timer_start_deadlock.c
new file mode 100644
index 000000000000..afabd15bdac4
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/timer_start_deadlock.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#define CLOCK_MONOTONIC 1
+
+char _license[] SEC("license") = "GPL";
+
+struct elem {
+	struct bpf_timer timer;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct elem);
+} timer_map SEC(".maps");
+
+volatile int in_timer_start;
+volatile int tp_called;
+
+static int timer_cb(void *map, int *key, struct elem *value)
+{
+	return 0;
+}
+
+SEC("tp_btf/hrtimer_start")
+int BPF_PROG(tp_hrtimer_start, struct hrtimer *hrtimer, enum hrtimer_mode mode, bool was_armed)
+{
+	struct bpf_timer *timer;
+	int key = 0;
+
+	if (!in_timer_start || !was_armed)
+		return 0;
+
+	tp_called = 1;
+	timer = bpf_map_lookup_elem(&timer_map, &key);
+
+	/*
+	 * Call bpf_timer_start() from the tracepoint within hrtimer logic
+	 * on the same timer to make sure it doesn't deadlock.
+	 */
+	bpf_timer_start(timer, 1000000000, 0);
+	return 0;
+}
+
+SEC("syscall")
+int start_timer(void *ctx)
+{
+	struct bpf_timer *timer;
+	int key = 0;
+
+	timer = bpf_map_lookup_elem(&timer_map, &key);
+	/* claude may complain here that there is no NULL check. Ignoring it. */
+	bpf_timer_init(timer, &timer_map, CLOCK_MONOTONIC);
+	bpf_timer_set_callback(timer, timer_cb);
+
+	/*
+	 * call hrtimer_start() twice, so that 2nd call does
+	 * trace_hrtimer_start(was_armed=1) tracepoint.
+	 */
+	in_timer_start = 1;
+	bpf_timer_start(timer, 1000000000, 0);
+	bpf_timer_start(timer, 1000000000, 0);
+	in_timer_start = 0;
+	return 0;
+}