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, 270 insertions, 0 deletions

diff --git a/drivers/dibs/dibs_main.c b/drivers/dibs/dibs_main.c
new file mode 100644
index 000000000..2b53a9d27
--- /dev/null
+++ b/drivers/dibs/dibs_main.c
@@ -0,0 +1,270 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  DIBS - Direct Internal Buffer Sharing
+ *
+ *  Implementation of the DIBS class module
+ *
+ *  Copyright IBM Corp. 2025
+ */
+#define pr_fmt(fmt) "dibs: " fmt
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/dibs.h>
+
+#include "dibs_loopback.h"
+
+MODULE_DESCRIPTION("Direct Internal Buffer Sharing class");
+MODULE_LICENSE("GPL");
+
+static const struct class dibs_class = {
+	.name		= "dibs",
+};
+
+/* use an array rather a list for fast mapping: */
+static struct dibs_client *clients[MAX_DIBS_CLIENTS];
+static u8 max_client;
+static DEFINE_MUTEX(clients_lock);
+struct dibs_dev_list {
+	struct list_head list;
+	struct mutex mutex; /* protects dibs device list */
+};
+
+static struct dibs_dev_list dibs_dev_list = {
+	.list = LIST_HEAD_INIT(dibs_dev_list.list),
+	.mutex = __MUTEX_INITIALIZER(dibs_dev_list.mutex),
+};
+
+static void dibs_setup_forwarding(struct dibs_client *client,
+				  struct dibs_dev *dibs)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&dibs->lock, flags);
+	dibs->subs[client->id] = client;
+	spin_unlock_irqrestore(&dibs->lock, flags);
+}
+
+int dibs_register_client(struct dibs_client *client)
+{
+	struct dibs_dev *dibs;
+	int i, rc = -ENOSPC;
+
+	mutex_lock(&dibs_dev_list.mutex);
+	mutex_lock(&clients_lock);
+	for (i = 0; i < MAX_DIBS_CLIENTS; ++i) {
+		if (!clients[i]) {
+			clients[i] = client;
+			client->id = i;
+			if (i == max_client)
+				max_client++;
+			rc = 0;
+			break;
+		}
+	}
+	mutex_unlock(&clients_lock);
+
+	if (i < MAX_DIBS_CLIENTS) {
+		/* initialize with all devices that we got so far */
+		list_for_each_entry(dibs, &dibs_dev_list.list, list) {
+			dibs->priv[i] = NULL;
+			client->ops->add_dev(dibs);
+			dibs_setup_forwarding(client, dibs);
+		}
+	}
+	mutex_unlock(&dibs_dev_list.mutex);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(dibs_register_client);
+
+int dibs_unregister_client(struct dibs_client *client)
+{
+	struct dibs_dev *dibs;
+	unsigned long flags;
+	int max_dmbs;
+	int rc = 0;
+
+	mutex_lock(&dibs_dev_list.mutex);
+	list_for_each_entry(dibs, &dibs_dev_list.list, list) {
+		spin_lock_irqsave(&dibs->lock, flags);
+		max_dmbs = dibs->ops->max_dmbs();
+		for (int i = 0; i < max_dmbs; ++i) {
+			if (dibs->dmb_clientid_arr[i] == client->id) {
+				WARN(1, "%s: attempt to unregister '%s' with registered dmb(s)\n",
+				     __func__, client->name);
+				rc = -EBUSY;
+				goto err_reg_dmb;
+			}
+		}
+		/* Stop forwarding IRQs and events */
+		dibs->subs[client->id] = NULL;
+		spin_unlock_irqrestore(&dibs->lock, flags);
+		clients[client->id]->ops->del_dev(dibs);
+		dibs->priv[client->id] = NULL;
+	}
+
+	mutex_lock(&clients_lock);
+	clients[client->id] = NULL;
+	if (client->id + 1 == max_client)
+		max_client--;
+	mutex_unlock(&clients_lock);
+
+	mutex_unlock(&dibs_dev_list.mutex);
+	return rc;
+
+err_reg_dmb:
+	spin_unlock_irqrestore(&dibs->lock, flags);
+	mutex_unlock(&dibs_dev_list.mutex);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(dibs_unregister_client);
+
+static void dibs_dev_release(struct device *dev)
+{
+	struct dibs_dev *dibs;
+
+	dibs = container_of(dev, struct dibs_dev, dev);
+
+	kfree(dibs->dmb_clientid_arr);
+	kfree(dibs);
+}
+
+struct dibs_dev *dibs_dev_alloc(void)
+{
+	struct dibs_dev *dibs;
+
+	dibs = kzalloc_obj(*dibs);
+	if (!dibs)
+		return dibs;
+	spin_lock_init(&dibs->lock);
+	dibs->dev.release = dibs_dev_release;
+	dibs->dev.class = &dibs_class;
+	device_initialize(&dibs->dev);
+
+	return dibs;
+}
+EXPORT_SYMBOL_GPL(dibs_dev_alloc);
+
+static ssize_t gid_show(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct dibs_dev *dibs;
+
+	dibs = container_of(dev, struct dibs_dev, dev);
+
+	return sysfs_emit(buf, "%pUb\n", &dibs->gid);
+}
+static DEVICE_ATTR_RO(gid);
+
+static ssize_t fabric_id_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct dibs_dev *dibs;
+	u16 fabric_id;
+
+	dibs = container_of(dev, struct dibs_dev, dev);
+	fabric_id = dibs->ops->get_fabric_id(dibs);
+
+	return sysfs_emit(buf, "0x%04x\n", fabric_id);
+}
+static DEVICE_ATTR_RO(fabric_id);
+
+static struct attribute *dibs_dev_attrs[] = {
+	&dev_attr_gid.attr,
+	&dev_attr_fabric_id.attr,
+	NULL,
+};
+
+static const struct attribute_group dibs_dev_attr_group = {
+	.attrs = dibs_dev_attrs,
+};
+
+int dibs_dev_add(struct dibs_dev *dibs)
+{
+	int max_dmbs;
+	int i, ret;
+
+	max_dmbs = dibs->ops->max_dmbs();
+	dibs->dmb_clientid_arr = kzalloc(max_dmbs, GFP_KERNEL);
+	if (!dibs->dmb_clientid_arr)
+		return -ENOMEM;
+	memset(dibs->dmb_clientid_arr, NO_DIBS_CLIENT, max_dmbs);
+
+	ret = device_add(&dibs->dev);
+	if (ret)
+		return ret;
+
+	ret = sysfs_create_group(&dibs->dev.kobj, &dibs_dev_attr_group);
+	if (ret) {
+		dev_err(&dibs->dev, "sysfs_create_group failed for dibs_dev\n");
+		device_del(&dibs->dev);
+		return ret;
+	}
+	mutex_lock(&dibs_dev_list.mutex);
+	mutex_lock(&clients_lock);
+	for (i = 0; i < max_client; ++i) {
+		if (clients[i]) {
+			clients[i]->ops->add_dev(dibs);
+			dibs_setup_forwarding(clients[i], dibs);
+		}
+	}
+	mutex_unlock(&clients_lock);
+	list_add(&dibs->list, &dibs_dev_list.list);
+	mutex_unlock(&dibs_dev_list.mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dibs_dev_add);
+
+void dibs_dev_del(struct dibs_dev *dibs)
+{
+	unsigned long flags;
+	int i;
+
+	sysfs_remove_group(&dibs->dev.kobj, &dibs_dev_attr_group);
+
+	spin_lock_irqsave(&dibs->lock, flags);
+	for (i = 0; i < MAX_DIBS_CLIENTS; ++i)
+		dibs->subs[i] = NULL;
+	spin_unlock_irqrestore(&dibs->lock, flags);
+
+	mutex_lock(&dibs_dev_list.mutex);
+	mutex_lock(&clients_lock);
+	for (i = 0; i < max_client; ++i) {
+		if (clients[i])
+			clients[i]->ops->del_dev(dibs);
+	}
+	mutex_unlock(&clients_lock);
+	list_del_init(&dibs->list);
+	mutex_unlock(&dibs_dev_list.mutex);
+
+	device_del(&dibs->dev);
+}
+EXPORT_SYMBOL_GPL(dibs_dev_del);
+
+static int __init dibs_init(void)
+{
+	int rc;
+
+	rc = class_register(&dibs_class);
+	if (rc)
+		return rc;
+
+	rc = dibs_loopback_init();
+	if (rc)
+		pr_err("%s fails with %d\n", __func__, rc);
+
+	return rc;
+}
+
+static void __exit dibs_exit(void)
+{
+	dibs_loopback_exit();
+	class_unregister(&dibs_class);
+}
+
+subsys_initcall(dibs_init);
+module_exit(dibs_exit);