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, 108 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/thread-utils.c b/drivers/md/dm-vdo/thread-utils.c
new file mode 100644
index 000000000..826afc952
--- /dev/null
+++ b/drivers/md/dm-vdo/thread-utils.c
@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#include "thread-utils.h"
+
+#include <asm/current.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/mutex.h>
+#include <linux/types.h>
+
+#include "errors.h"
+#include "logger.h"
+#include "memory-alloc.h"
+
+static struct hlist_head thread_list;
+static struct mutex thread_mutex;
+
+struct thread {
+	void (*thread_function)(void *thread_data);
+	void *thread_data;
+	struct hlist_node thread_links;
+	struct task_struct *thread_task;
+	struct completion thread_done;
+};
+
+void vdo_initialize_threads_mutex(void)
+{
+	mutex_init(&thread_mutex);
+}
+
+static int thread_starter(void *arg)
+{
+	struct registered_thread allocating_thread;
+	struct thread *thread = arg;
+
+	thread->thread_task = current;
+	mutex_lock(&thread_mutex);
+	hlist_add_head(&thread->thread_links, &thread_list);
+	mutex_unlock(&thread_mutex);
+	vdo_register_allocating_thread(&allocating_thread, NULL);
+	thread->thread_function(thread->thread_data);
+	vdo_unregister_allocating_thread();
+	complete(&thread->thread_done);
+	return 0;
+}
+
+int vdo_create_thread(void (*thread_function)(void *), void *thread_data,
+		      const char *name, struct thread **new_thread)
+{
+	char *name_colon = strchr(name, ':');
+	char *my_name_colon = strchr(current->comm, ':');
+	struct task_struct *task;
+	struct thread *thread;
+	int result;
+
+	result = vdo_allocate(1, __func__, &thread);
+	if (result != VDO_SUCCESS) {
+		vdo_log_warning("Error allocating memory for %s", name);
+		return result;
+	}
+
+	thread->thread_function = thread_function;
+	thread->thread_data = thread_data;
+	init_completion(&thread->thread_done);
+	/*
+	 * Start the thread, with an appropriate thread name.
+	 *
+	 * If the name supplied contains a colon character, use that name. This causes uds module
+	 * threads to have names like "uds:callbackW" and the main test runner thread to be named
+	 * "zub:runtest".
+	 *
+	 * Otherwise if the current thread has a name containing a colon character, prefix the name
+	 * supplied with the name of the current thread up to (and including) the colon character.
+	 * Thus when the "kvdo0:dedupeQ" thread opens an index session, all the threads associated
+	 * with that index will have names like "kvdo0:foo".
+	 *
+	 * Otherwise just use the name supplied. This should be a rare occurrence.
+	 */
+	if ((name_colon == NULL) && (my_name_colon != NULL)) {
+		task = kthread_run(thread_starter, thread, "%.*s:%s",
+				   (int) (my_name_colon - current->comm), current->comm,
+				   name);
+	} else {
+		task = kthread_run(thread_starter, thread, "%s", name);
+	}
+
+	if (IS_ERR(task)) {
+		vdo_free(thread);
+		return PTR_ERR(task);
+	}
+
+	*new_thread = thread;
+	return VDO_SUCCESS;
+}
+
+void vdo_join_threads(struct thread *thread)
+{
+	while (wait_for_completion_interruptible(&thread->thread_done))
+		fsleep(1000);
+
+	mutex_lock(&thread_mutex);
+	hlist_del(&thread->thread_links);
+	mutex_unlock(&thread_mutex);
+	vdo_free(thread);
+}