selftests/bpf: Add tests for preempt kfuncs

Add tests for nested cases, nested count preservation upon different
subprog calls that disable/enable preemption, and test sleepable helper
call in non-preemptible regions.

182/1   preempt_lock/preempt_lock_missing_1:OK
182/2   preempt_lock/preempt_lock_missing_2:OK
182/3   preempt_lock/preempt_lock_missing_3:OK
182/4   preempt_lock/preempt_lock_missing_3_minus_2:OK
182/5   preempt_lock/preempt_lock_missing_1_subprog:OK
182/6   preempt_lock/preempt_lock_missing_2_subprog:OK
182/7   preempt_lock/preempt_lock_missing_2_minus_1_subprog:OK
182/8   preempt_lock/preempt_balance:OK
182/9   preempt_lock/preempt_balance_subprog_test:OK
182/10  preempt_lock/preempt_global_subprog_test:OK
182/11  preempt_lock/preempt_sleepable_helper:OK
182     preempt_lock:OK
Summary: 1/11 PASSED, 0 SKIPPED, 0 FAILED
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20240424031315.2757363-3-memxor@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

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

+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <network_helpers.h>
+#include <preempt_lock.skel.h>
+
+void test_preempt_lock(void)
+{
+	RUN_TESTS(preempt_lock);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+void bpf_preempt_disable(void) __ksym;
+void bpf_preempt_enable(void) __ksym;
+
+SEC("?tc")
+__failure __msg("1 bpf_preempt_enable is missing")
+int preempt_lock_missing_1(struct __sk_buff *ctx)
+{
+	bpf_preempt_disable();
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("2 bpf_preempt_enable(s) are missing")
+int preempt_lock_missing_2(struct __sk_buff *ctx)
+{
+	bpf_preempt_disable();
+	bpf_preempt_disable();
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("3 bpf_preempt_enable(s) are missing")
+int preempt_lock_missing_3(struct __sk_buff *ctx)
+{
+	bpf_preempt_disable();
+	bpf_preempt_disable();
+	bpf_preempt_disable();
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("1 bpf_preempt_enable is missing")
+int preempt_lock_missing_3_minus_2(struct __sk_buff *ctx)
+{
+	bpf_preempt_disable();
+	bpf_preempt_disable();
+	bpf_preempt_disable();
+	bpf_preempt_enable();
+	bpf_preempt_enable();
+	return 0;
+}
+
+static __noinline void preempt_disable(void)
+{
+	bpf_preempt_disable();
+}
+
+static __noinline void preempt_enable(void)
+{
+	bpf_preempt_enable();
+}
+
+SEC("?tc")
+__failure __msg("1 bpf_preempt_enable is missing")
+int preempt_lock_missing_1_subprog(struct __sk_buff *ctx)
+{
+	preempt_disable();
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("2 bpf_preempt_enable(s) are missing")
+int preempt_lock_missing_2_subprog(struct __sk_buff *ctx)
+{
+	preempt_disable();
+	preempt_disable();
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("1 bpf_preempt_enable is missing")
+int preempt_lock_missing_2_minus_1_subprog(struct __sk_buff *ctx)
+{
+	preempt_disable();
+	preempt_disable();
+	preempt_enable();
+	return 0;
+}
+
+static __noinline void preempt_balance_subprog(void)
+{
+	preempt_disable();
+	preempt_enable();
+}
+
+SEC("?tc")
+__success int preempt_balance(struct __sk_buff *ctx)
+{
+	bpf_preempt_disable();
+	bpf_preempt_enable();
+	return 0;
+}
+
+SEC("?tc")
+__success int preempt_balance_subprog_test(struct __sk_buff *ctx)
+{
+	preempt_balance_subprog();
+	return 0;
+}
+
+SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
+__failure __msg("sleepable helper bpf_copy_from_user#")
+int preempt_sleepable_helper(void *ctx)
+{
+	u32 data;
+
+	bpf_preempt_disable();
+	bpf_copy_from_user(&data, sizeof(data), NULL);
+	bpf_preempt_enable();
+	return 0;
+}
+
+int __noinline preempt_global_subprog(void)
+{
+	preempt_balance_subprog();
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("global function calls are not allowed with preemption disabled")
+int preempt_global_subprog_test(struct __sk_buff *ctx)
+{
+	preempt_disable();
+	preempt_global_subprog();
+	preempt_enable();
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";