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, 103 insertions, 0 deletions

diff --git a/drivers/dax/hmem/device.c b/drivers/dax/hmem/device.c
new file mode 100644
index 000000000..d70359b43
--- /dev/null
+++ b/drivers/dax/hmem/device.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/platform_device.h>
+#include <linux/memregion.h>
+#include <linux/module.h>
+#include <linux/dax.h>
+#include <linux/mm.h>
+#include "../bus.h"
+
+static bool nohmem;
+module_param_named(disable, nohmem, bool, 0444);
+
+static bool platform_initialized;
+static DEFINE_MUTEX(hmem_resource_lock);
+static struct resource hmem_active = {
+	.name = "HMEM devices",
+	.start = 0,
+	.end = -1,
+	.flags = IORESOURCE_MEM,
+};
+
+int walk_hmem_resources(struct device *host, walk_hmem_fn fn)
+{
+	struct resource *res;
+	int rc = 0;
+
+	mutex_lock(&hmem_resource_lock);
+	for (res = hmem_active.child; res; res = res->sibling) {
+		rc = fn(host, (int) res->desc, res);
+		if (rc)
+			break;
+	}
+	mutex_unlock(&hmem_resource_lock);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(walk_hmem_resources);
+
+static void hmem_work(struct work_struct *work)
+{
+	/* place holder until dax_hmem driver attaches */
+}
+
+static struct hmem_platform_device hmem_platform = {
+	.pdev = {
+		.name = "hmem_platform",
+		.id = 0,
+	},
+	.work = __WORK_INITIALIZER(hmem_platform.work, hmem_work),
+};
+
+static void __hmem_register_resource(int target_nid, struct resource *res)
+{
+	struct resource *new;
+	int rc;
+
+	new = __request_region(&hmem_active, res->start, resource_size(res), "",
+			       0);
+	if (!new) {
+		pr_debug("hmem range %pr already active\n", res);
+		return;
+	}
+
+	new->desc = target_nid;
+
+	if (platform_initialized)
+		return;
+
+	rc = platform_device_register(&hmem_platform.pdev);
+	if (rc) {
+		pr_err_once("failed to register device-dax hmem_platform device\n");
+		return;
+	}
+
+	platform_initialized = true;
+}
+
+void hmem_register_resource(int target_nid, struct resource *res)
+{
+	if (nohmem)
+		return;
+
+	mutex_lock(&hmem_resource_lock);
+	__hmem_register_resource(target_nid, res);
+	mutex_unlock(&hmem_resource_lock);
+}
+
+static __init int hmem_register_one(struct resource *res, void *data)
+{
+	hmem_register_resource(phys_to_target_node(res->start), res);
+
+	return 0;
+}
+
+static __init int hmem_init(void)
+{
+	walk_soft_reserve_res(0, -1, NULL, hmem_register_one);
+	return 0;
+}
+
+/*
+ * As this is a fallback for address ranges unclaimed by the ACPI HMAT
+ * parsing it must be at an initcall level greater than hmat_init().
+ */
+device_initcall(hmem_init);