selftests/bpf: Add a test for objects stuck in free_by_rcu_ttracegrafted

Delete all elements of BPF_F_NO_PREALLOC hash map in one batch. The first
free_bulk() starts RCU tasks trace GP and the rest of the elements are
freed while it's in flight. Wait for call_rcu_ttrace_in_progress to clear
in bpf_mem_cache of every cpu and check that free_by_rcu_ttrace and
waiting_for_gp_ttrace lists are empty.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20260930095920.601738-4-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

2 files changed, 78 insertions, 0 deletions

diff --git a/samples/user_events/Makefile b/samples/user_events/Makefile
new file mode 100644
index 000000000..7252b589d
--- /dev/null
+++ b/samples/user_events/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS += -Wl,-no-as-needed -Wall -I../../usr/include
+
+example: example.o
+example.o: example.c
diff --git a/samples/user_events/example.c b/samples/user_events/example.c
new file mode 100644
index 000000000..28165a096
--- /dev/null
+++ b/samples/user_events/example.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2021, Microsoft Corporation.
+ *
+ * Authors:
+ *   Beau Belgrave <beaub@linux.microsoft.com>
+ */
+
+#include <errno.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/uio.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <linux/user_events.h>
+
+const char *data_file = "/sys/kernel/tracing/user_events_data";
+int enabled = 0;
+
+static int event_reg(int fd, const char *command, int *write, int *enabled)
+{
+	struct user_reg reg = {0};
+
+	reg.size = sizeof(reg);
+	reg.enable_bit = 31;
+	reg.enable_size = sizeof(*enabled);
+	reg.enable_addr = (__u64)enabled;
+	reg.name_args = (__u64)command;
+
+	if (ioctl(fd, DIAG_IOCSREG, &reg) == -1)
+		return -1;
+
+	*write = reg.write_index;
+
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	int data_fd, write;
+	struct iovec io[2];
+	__u32 count = 0;
+
+	data_fd = open(data_file, O_RDWR);
+
+	if (event_reg(data_fd, "test u32 count", &write, &enabled) == -1)
+		return errno;
+
+	/* Setup iovec */
+	io[0].iov_base = &write;
+	io[0].iov_len = sizeof(write);
+	io[1].iov_base = &count;
+	io[1].iov_len = sizeof(count);
+ask:
+	printf("Press enter to check status...\n");
+	getchar();
+
+	/* Check if anyone is listening */
+	if (enabled) {
+		/* Yep, trace out our data */
+		writev(data_fd, (const struct iovec *)io, 2);
+
+		/* Increase the count */
+		count++;
+
+		printf("Something was attached, wrote data\n");
+	}
+
+	goto ask;
+
+	return 0;
+}