ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 116 insertions, 0 deletions

diff --git a/lib/test_memcat_p.c b/lib/test_memcat_p.c
new file mode 100644
index 000000000..62f1633b3
--- /dev/null
+++ b/lib/test_memcat_p.c
@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test cases for memcat_p() in lib/memcat_p.c
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+
+struct test_struct {
+	int		num;
+	unsigned int	magic;
+};
+
+#define MAGIC		0xf00ff00f
+/* Size of each of the NULL-terminated input arrays */
+#define INPUT_MAX	128
+/* Expected number of non-NULL elements in the output array */
+#define EXPECT		(INPUT_MAX * 2 - 2)
+
+static int __init test_memcat_p_init(void)
+{
+	struct test_struct **in0, **in1, **out, **p;
+	int err = -ENOMEM, i, r, total = 0;
+
+	in0 = kzalloc_objs(*in0, INPUT_MAX);
+	if (!in0)
+		return err;
+
+	in1 = kzalloc_objs(*in1, INPUT_MAX);
+	if (!in1)
+		goto err_free_in0;
+
+	for (i = 0, r = 1; i < INPUT_MAX - 1; i++) {
+		in0[i] = kmalloc_obj(**in0);
+		if (!in0[i])
+			goto err_free_elements;
+
+		in1[i] = kmalloc_obj(**in1);
+		if (!in1[i]) {
+			kfree(in0[i]);
+			goto err_free_elements;
+		}
+
+		/* lifted from test_sort.c */
+		r = (r * 725861) % 6599;
+		in0[i]->num = r;
+		in1[i]->num = -r;
+		in0[i]->magic = MAGIC;
+		in1[i]->magic = MAGIC;
+	}
+
+	in0[i] = in1[i] = NULL;
+
+	out = memcat_p(in0, in1);
+	if (!out)
+		goto err_free_all_elements;
+
+	err = -EINVAL;
+	for (i = 0, p = out; *p && (i < INPUT_MAX * 2 - 1); p++, i++) {
+		total += (*p)->num;
+
+		if ((*p)->magic != MAGIC) {
+			pr_err("test failed: wrong magic at %d: %u\n", i,
+			       (*p)->magic);
+			goto err_free_out;
+		}
+	}
+
+	if (total) {
+		pr_err("test failed: expected zero total, got %d\n", total);
+		goto err_free_out;
+	}
+
+	if (i != EXPECT) {
+		pr_err("test failed: expected output size %d, got %d\n",
+		       EXPECT, i);
+		goto err_free_out;
+	}
+
+	for (i = 0; i < INPUT_MAX - 1; i++)
+		if (out[i] != in0[i] || out[i + INPUT_MAX - 1] != in1[i]) {
+			pr_err("test failed: wrong element order at %d\n", i);
+			goto err_free_out;
+		}
+
+	err = 0;
+	pr_info("test passed\n");
+
+err_free_out:
+	kfree(out);
+err_free_all_elements:
+	i = INPUT_MAX;
+err_free_elements:
+	for (i--; i >= 0; i--) {
+		kfree(in1[i]);
+		kfree(in0[i]);
+	}
+
+	kfree(in1);
+err_free_in0:
+	kfree(in0);
+
+	return err;
+}
+
+static void __exit test_memcat_p_exit(void)
+{
+}
+
+module_init(test_memcat_p_init);
+module_exit(test_memcat_p_exit);
+
+MODULE_DESCRIPTION("Test cases for memcat_p() in lib/memcat_p.c");
+MODULE_LICENSE("GPL");