selftests/bpf: Test deadlock from recursive bpf_task_storage_[get|delete]

Add a test with recursive bpf_task_storage_[get|delete] from fentry
programs on bpf_local_storage_lookup and bpf_local_storage_update. Without
proper deadlock prevent mechanism, this test would cause deadlock.
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210225234319.336131-5-songliubraving@fb.com

tools/testing/selftests/bpf/prog_tests/task_local_storage.c

@@ -8,6 +8,7 @@
 #include <test_progs.h>
 #include "task_local_storage.skel.h"
 #include "task_local_storage_exit_creds.skel.h"
+#include "task_ls_recursion.skel.h"
 
 static void test_sys_enter_exit(void)
 {
@@ -60,10 +61,32 @@ static void test_exit_creds(void)
 	task_local_storage_exit_creds__destroy(skel);
 }
 
+static void test_recursion(void)
+{
+	struct task_ls_recursion *skel;
+	int err;
+
+	skel = task_ls_recursion__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
+		return;
+
+	err = task_ls_recursion__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto out;
+
+	/* trigger sys_enter, make sure it does not cause deadlock */
+	syscall(SYS_gettid);
+
+out:
+	task_ls_recursion__destroy(skel);
+}
+
 void test_task_local_storage(void)
 {
 	if (test__start_subtest("sys_enter_exit"))
 		test_sys_enter_exit();
 	if (test__start_subtest("exit_creds"))
 		test_exit_creds();
+	if (test__start_subtest("recursion"))
+		test_recursion();
 }

tools/testing/selftests/bpf/progs/task_ls_recursion.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, long);
+} map_a SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, long);
+} map_b SEC(".maps");
+
+SEC("fentry/bpf_local_storage_lookup")
+int BPF_PROG(on_lookup)
+{
+	struct task_struct *task = bpf_get_current_task_btf();
+
+	bpf_task_storage_delete(&map_a, task);
+	bpf_task_storage_delete(&map_b, task);
+	return 0;
+}
+
+SEC("fentry/bpf_local_storage_update")
+int BPF_PROG(on_update)
+{
+	struct task_struct *task = bpf_get_current_task_btf();
+	long *ptr;
+
+	ptr = bpf_task_storage_get(&map_a, task, 0,
+				   BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (ptr)
+		*ptr += 1;
+
+	ptr = bpf_task_storage_get(&map_b, task, 0,
+				   BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (ptr)
+		*ptr += 1;
+
+	return 0;
+}
+
+SEC("tp_btf/sys_enter")
+int BPF_PROG(on_enter, struct pt_regs *regs, long id)
+{
+	struct task_struct *task;
+	long *ptr;
+
+	task = bpf_get_current_task_btf();
+	ptr = bpf_task_storage_get(&map_a, task, 0,
+				   BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (ptr)
+		*ptr = 200;
+
+	ptr = bpf_task_storage_get(&map_b, task, 0,
+				   BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (ptr)
+		*ptr = 100;
+	return 0;
+}