[RFC PATCH v2 3/3] selftests/bpf: exercise task storage from hrtimer_start

[Karl Mehltretter <kmehltretter@gmail.com>]

No BPF selftest creates task-local storage from a tracepoint which runs
while an hrtimer base raw lock is held.  On PREEMPT_RT, this can exercise
allocator rtmutexes inside a raw-lock section.

Attach a program to tp_btf/hrtimer_start for the test process.  Create and
delete task storage on every event and trigger 1,000 events with
timerfd_settime().  Detach the program before reading its counters, then
require at least one successful allocation and balanced attempt and
outcome counters.  Allocation failure remains valid for the best-effort
no-lock API.

Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
---
 .../bpf/prog_tests/task_storage_hrtimer.c     | 50 +++++++++++++++++++
 .../bpf/progs/task_storage_hrtimer.c          | 48 ++++++++++++++++++
 2 files changed, 98 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/task_storage_hrtimer.c
 create mode 100644 tools/testing/selftests/bpf/progs/task_storage_hrtimer.c

diff --git a/tools/testing/selftests/bpf/prog_tests/task_storage_hrtimer.c b/tools/testing/selftests/bpf/prog_tests/task_storage_hrtimer.c
new file mode 100644
index 000000000000..216e66263bf6
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/task_storage_hrtimer.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <sys/timerfd.h>
+#include <unistd.h>
+
+#include <test_progs.h>
+#include "task_storage_hrtimer.skel.h"
+
+#define TRIGGER_COUNT 1000
+
+void test_task_storage_hrtimer(void)
+{
+	struct itimerspec timer = {
+		.it_value.tv_nsec = 1000000,
+	};
+	struct task_storage_hrtimer *skel;
+	int err, fd = -1, i;
+
+	skel = task_storage_hrtimer__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
+		return;
+
+	skel->bss->target_tgid = getpid();
+	err = task_storage_hrtimer__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto cleanup;
+
+	fd = timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC);
+	if (!ASSERT_GE(fd, 0, "timerfd_create"))
+		goto cleanup;
+
+	for (i = 0; i < TRIGGER_COUNT; i++) {
+		err = timerfd_settime(fd, 0, &timer, NULL);
+		if (!ASSERT_OK(err, "timerfd_settime"))
+			goto cleanup;
+	}
+
+	task_storage_hrtimer__detach(skel);
+
+	ASSERT_GE(skel->bss->seen, TRIGGER_COUNT, "seen");
+	ASSERT_EQ(skel->bss->attempted, skel->bss->seen, "attempted");
+	ASSERT_GT(skel->bss->succeeded, 0, "succeeded");
+	ASSERT_EQ(skel->bss->delete_errors, 0, "delete_errors");
+	ASSERT_EQ(skel->bss->attempted,
+		  skel->bss->succeeded + skel->bss->failed, "attempts");
+
+cleanup:
+	if (fd >= 0)
+		close(fd);
+	task_storage_hrtimer__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/task_storage_hrtimer.c b/tools/testing/selftests/bpf/progs/task_storage_hrtimer.c
new file mode 100644
index 000000000000..a53c966f15b5
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/task_storage_hrtimer.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+#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);
+} task_storage SEC(".maps");
+
+u32 target_tgid;
+u64 seen;
+u64 attempted;
+u64 succeeded;
+u64 failed;
+u64 delete_errors;
+
+SEC("tp_btf/hrtimer_start")
+int BPF_PROG(on_hrtimer_start, struct hrtimer *timer,
+	     enum hrtimer_mode mode, bool was_armed)
+{
+	struct task_struct *task;
+	long *storage;
+
+	if (bpf_get_current_pid_tgid() >> 32 != target_tgid)
+		return 0;
+
+	seen++;
+	attempted++;
+	task = bpf_get_current_task_btf();
+	storage = bpf_task_storage_get(&task_storage, task, NULL,
+				       BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (!storage) {
+		failed++;
+		return 0;
+	}
+
+	if (bpf_task_storage_delete(&task_storage, task))
+		delete_errors++;
+	else
+		succeeded++;
+
+	return 0;
+}
-- 
2.53.0