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>

1 files changed, 79 insertions, 0 deletions

diff --git a/tools/testing/radix-tree/regression4.c b/tools/testing/radix-tree/regression4.c
new file mode 100644
index 000000000..cf4e5aba6
--- /dev/null
+++ b/tools/testing/radix-tree/regression4.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/gfp.h>
+#include <linux/slab.h>
+#include <linux/radix-tree.h>
+#include <linux/rcupdate.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <assert.h>
+
+#include "regression.h"
+
+static pthread_barrier_t worker_barrier;
+static int obj0, obj1;
+static RADIX_TREE(mt_tree, GFP_KERNEL);
+
+static void *reader_fn(void *arg)
+{
+	int i;
+	void *entry;
+
+	rcu_register_thread();
+	pthread_barrier_wait(&worker_barrier);
+
+	for (i = 0; i < 1000000; i++) {
+		rcu_read_lock();
+		entry = radix_tree_lookup(&mt_tree, 0);
+		rcu_read_unlock();
+		if (entry != &obj0) {
+			printf("iteration %d bad entry = %p\n", i, entry);
+			abort();
+		}
+	}
+
+	rcu_unregister_thread();
+
+	return NULL;
+}
+
+static void *writer_fn(void *arg)
+{
+	int i;
+
+	rcu_register_thread();
+	pthread_barrier_wait(&worker_barrier);
+
+	for (i = 0; i < 1000000; i++) {
+		radix_tree_insert(&mt_tree, 1, &obj1);
+		radix_tree_delete(&mt_tree, 1);
+	}
+
+	rcu_unregister_thread();
+
+	return NULL;
+}
+
+void regression4_test(void)
+{
+	pthread_t reader, writer;
+
+	printv(1, "regression test 4 starting\n");
+
+	radix_tree_insert(&mt_tree, 0, &obj0);
+	pthread_barrier_init(&worker_barrier, NULL, 2);
+
+	if (pthread_create(&reader, NULL, reader_fn, NULL) ||
+	    pthread_create(&writer, NULL, writer_fn, NULL)) {
+		perror("pthread_create");
+		exit(1);
+	}
+
+	if (pthread_join(reader, NULL) || pthread_join(writer, NULL)) {
+		perror("pthread_join");
+		exit(1);
+	}
+
+	printv(1, "regression test 4 passed\n");
+}