selftests/bpf: add bpf task work stress tests

Add stress tests for BPF task-work scheduling kfuncs. The tests spawn
multiple threads that concurrently schedule task_work callbacks against
the same and different map values to exercise the kfuncs under high
contention.
Verify callbacks are reliably enqueued and executed with no drops.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Link: https://lore.kernel.org/r/20250923112404.668720-10-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 73 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/task_work_stress.c b/tools/testing/selftests/bpf/progs/task_work_stress.c
new file mode 100644
index 000000000000..90fca06fff56
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/task_work_stress.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <string.h>
+#include <stdbool.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+#define ENTRIES 128
+
+char _license[] SEC("license") = "GPL";
+
+__u64 callback_scheduled = 0;
+__u64 callback_success = 0;
+__u64 schedule_error = 0;
+__u64 delete_success = 0;
+
+struct elem {
+	__u32 count;
+	struct bpf_task_work tw;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__uint(max_entries, ENTRIES);
+	__type(key, int);
+	__type(value, struct elem);
+} hmap SEC(".maps");
+
+static int process_work(struct bpf_map *map, void *key, void *value)
+{
+	__sync_fetch_and_add(&callback_success, 1);
+	return 0;
+}
+
+SEC("syscall")
+int schedule_task_work(void *ctx)
+{
+	struct elem empty_work = {.count = 0};
+	struct elem *work;
+	int key = 0, err;
+
+	key = bpf_ktime_get_ns() % ENTRIES;
+	work = bpf_map_lookup_elem(&hmap, &key);
+	if (!work) {
+		bpf_map_update_elem(&hmap, &key, &empty_work, BPF_NOEXIST);
+		work = bpf_map_lookup_elem(&hmap, &key);
+		if (!work)
+			return 0;
+	}
+	err = bpf_task_work_schedule_signal(bpf_get_current_task_btf(), &work->tw, &hmap,
+					    process_work, NULL);
+	if (err)
+		__sync_fetch_and_add(&schedule_error, 1);
+	else
+		__sync_fetch_and_add(&callback_scheduled, 1);
+	return 0;
+}
+
+SEC("syscall")
+int delete_task_work(void *ctx)
+{
+	int key = 0, err;
+
+	key = bpf_get_prandom_u32() % ENTRIES;
+	err = bpf_map_delete_elem(&hmap, &key);
+	if (!err)
+		__sync_fetch_and_add(&delete_success, 1);
+	return 0;
+}