bpf: Reject bpf_timer for PREEMPT_RT

While running './test_progs -t timer' to validate the test case from "selftests/bpf: Introduce experimental bpf_in_interrupt()"[0] for PREEMPT_RT, I encountered a kernel warning:

BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48

To address this, reject bpf_timer usage in the verifier when PREEMPT_RT is enabled, and skip the corresponding timer selftests.

Changes:
v2 -> v3:
* Drop skipping test case 'timer_interrupt'.
* Address comments from Alexei:
* Respin targeting bpf tree.
* Trim commit log.

v1 -> v2:
* Skip test case 'timer_interrupt'.

Links:
[0] https://lore.kernel.org/bpf/[email protected]/

Leon Hwang (2):
bpf: Reject bpf_timer for PREEMPT_RT
selftests/bpf: Skip timer cases when bpf_timer is not supported

 kernel/bpf/verifier.c                                 | 4 ++++
 tools/testing/selftests/bpf/prog_tests/free_timer.c   | 4 ++++
 tools/testing/selftests/bpf/prog_tests/timer.c        | 4 ++++
 tools/testing/selftests/bpf/prog_tests/timer_crash.c  | 4 ++++
 tools/testing/selftests/bpf/prog_tests/timer_lockup.c | 4 ++++
 tools/testing/selftests/bpf/prog_tests/timer_mim.c    | 4 ++++
 6 files changed, 24 insertions(+)

--
2.50.1

When enable CONFIG_PREEMPT_RT, the kernel will warn when run timer selftests by './test_progs -t timer':

BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48

In order to avoid such warning, reject bpf_timer in verifier when PREEMPT_RT is enabled.

---
 kernel/bpf/verifier.c | 4 ++++
 1 file changed, 4 insertions(+)

index c89e2b1bc644b..9fb1f957a0937 100644
@@ -8547,6 +8547,10 @@ static int process_timer_func(struct bpf_verifier_env *env, int regno,
 		verifier_bug(env, "Two map pointers in a timer helper");
 		return -EFAULT;
 	}
+	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		verbose(env, "bpf_timer cannot be used for PREEMPT_RT.\n");
+		return -EOPNOTSUPP;
+	}
 	meta->map_uid = reg->map_uid;
 	meta->map_ptr = map;
 	return 0;

2.50.1

When enable CONFIG_PREEMPT_RT, verifier will reject bpf_timer with returning -EOPNOTSUPP.

Therefore, skip test cases when errno is EOPNOTSUPP.

cd tools/testing/selftests/bpf
./test_progs -t timer

125     free_timer:SKIP
456     timer:SKIP
457/1   timer_crash/array:SKIP
457/2   timer_crash/hash:SKIP
457     timer_crash:SKIP
458     timer_lockup:SKIP
459     timer_mim:SKIP

Summary: 5/0 PASSED, 6 SKIPPED, 0 FAILED

---
 tools/testing/selftests/bpf/prog_tests/free_timer.c   | 4 ++++
 tools/testing/selftests/bpf/prog_tests/timer.c        | 4 ++++
 tools/testing/selftests/bpf/prog_tests/timer_crash.c  | 4 ++++
 tools/testing/selftests/bpf/prog_tests/timer_lockup.c | 4 ++++
 tools/testing/selftests/bpf/prog_tests/timer_mim.c    | 4 ++++
 5 files changed, 20 insertions(+)

index b7b77a6b29799..0de8facca4c5b 100644
@@ -124,6 +124,10 @@ void test_free_timer(void)
 	int err;
 
 	skel = free_timer__open_and_load();
+	if (!skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(skel, "open_load"))
 		return;
 

index d66687f1ee6a8..56f660ca567ba 100644
@@ -86,6 +86,10 @@ void serial_test_timer(void)
 	int err;
 
 	timer_skel = timer__open_and_load();
+	if (!timer_skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(timer_skel, "timer_skel_load"))
 		return;
 

index f74b82305da8c..b841597c8a3a3 100644
@@ -12,6 +12,10 @@ static void test_timer_crash_mode(int mode)
 	struct timer_crash *skel;
 
 	skel = timer_crash__open_and_load();
+	if (!skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(skel, "timer_crash__open_and_load"))
 		return;
 	skel->bss->pid = getpid();

index 1a2f99596916f..eb303fa1e09af 100644
@@ -59,6 +59,10 @@ void test_timer_lockup(void)
 	}
 
 	skel = timer_lockup__open_and_load();
+	if (!skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(skel, "timer_lockup__open_and_load"))
 		return;
 

index 9ff7843909e7d..c930c7d7105b9 100644
@@ -65,6 +65,10 @@ void serial_test_timer_mim(void)
 		goto cleanup;
 
 	timer_skel = timer_mim__open_and_load();
+	if (!timer_skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(timer_skel, "timer_skel_load"))
 		goto cleanup;
 

2.50.1