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, 75 insertions, 0 deletions

diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
new file mode 100644
index 000000000..3ab39b778
--- /dev/null
+++ b/drivers/dax/cxl.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright(c) 2023 Intel Corporation. All rights reserved. */
+#include <linux/module.h>
+#include <linux/dax.h>
+
+#include "../cxl/cxl.h"
+#include "bus.h"
+
+static int cxl_dax_region_probe(struct device *dev)
+{
+	struct cxl_dax_region *cxlr_dax = to_cxl_dax_region(dev);
+	int nid = phys_to_target_node(cxlr_dax->hpa_range.start);
+	struct cxl_region *cxlr = cxlr_dax->cxlr;
+	struct dax_region *dax_region;
+	struct dev_dax_data data;
+
+	if (nid == NUMA_NO_NODE)
+		nid = memory_add_physaddr_to_nid(cxlr_dax->hpa_range.start);
+
+	dax_region = alloc_dax_region(dev, cxlr->id, &cxlr_dax->hpa_range, nid,
+				      PMD_SIZE, IORESOURCE_DAX_KMEM);
+	if (!dax_region)
+		return -ENOMEM;
+
+	data = (struct dev_dax_data) {
+		.dax_region = dax_region,
+		.id = -1,
+		.size = range_len(&cxlr_dax->hpa_range),
+		.memmap_on_memory = true,
+	};
+
+	return PTR_ERR_OR_ZERO(devm_create_dev_dax(&data));
+}
+
+static struct cxl_driver cxl_dax_region_driver = {
+	.name = "cxl_dax_region",
+	.probe = cxl_dax_region_probe,
+	.id = CXL_DEVICE_DAX_REGION,
+	.drv = {
+		.suppress_bind_attrs = true,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+
+static void cxl_dax_region_driver_register(struct work_struct *work)
+{
+	dax_hmem_flush_work();
+	cxl_driver_register(&cxl_dax_region_driver);
+}
+
+static DECLARE_WORK(cxl_dax_region_driver_work, cxl_dax_region_driver_register);
+
+static int __init cxl_dax_region_init(void)
+{
+	/*
+	 * Need to resolve a race with dax_hmem wanting to drive regions
+	 * instead of CXL
+	 */
+	queue_work(system_long_wq, &cxl_dax_region_driver_work);
+	return 0;
+}
+module_init(cxl_dax_region_init);
+
+static void __exit cxl_dax_region_exit(void)
+{
+	flush_work(&cxl_dax_region_driver_work);
+	cxl_driver_unregister(&cxl_dax_region_driver);
+}
+module_exit(cxl_dax_region_exit);
+
+MODULE_ALIAS_CXL(CXL_DEVICE_DAX_REGION);
+MODULE_DESCRIPTION("CXL DAX: direct access to CXL regions");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Intel Corporation");
+MODULE_IMPORT_NS("CXL");