1// SPDX-License-Identifier: GPL-2.0-only
 2/*
 3 * Copyright 2023 Red Hat
 4 */
 5
 6#include "thread-registry.h"
 7
 8#include <asm/current.h>
 9#include <linux/rculist.h>
10
11#include "permassert.h"
12
13/*
14 * We need to be careful when using other facilities that may use thread registry functions in
15 * their normal operation. For example, we do not want to invoke the logger while holding a lock.
16 */
17
18void vdo_initialize_thread_registry(struct thread_registry *registry)
19{
20	INIT_LIST_HEAD(&registry->links);
21	spin_lock_init(&registry->lock);
22}
23
24/* Register the current thread and associate it with a data pointer. */
25void vdo_register_thread(struct thread_registry *registry,
26			 struct registered_thread *new_thread, const void *pointer)
27{
28	struct registered_thread *thread;
29	bool found_it = false;
30
31	INIT_LIST_HEAD(&new_thread->links);
32	new_thread->pointer = pointer;
33	new_thread->task = current;
34
35	spin_lock(&registry->lock);
36	list_for_each_entry(thread, &registry->links, links) {
37		if (thread->task == current) {
38			/* There should be no existing entry. */
39			list_del_rcu(&thread->links);
40			found_it = true;
41			break;
42		}
43	}
44	list_add_tail_rcu(&new_thread->links, &registry->links);
45	spin_unlock(&registry->lock);
46
47	VDO_ASSERT_LOG_ONLY(!found_it, "new thread not already in registry");
48	if (found_it) {
49		/* Ensure no RCU iterators see it before re-initializing. */
50		synchronize_rcu();
51		INIT_LIST_HEAD(&thread->links);
52	}
53}
54
55void vdo_unregister_thread(struct thread_registry *registry)
56{
57	struct registered_thread *thread;
58	bool found_it = false;
59
60	spin_lock(&registry->lock);
61	list_for_each_entry(thread, &registry->links, links) {
62		if (thread->task == current) {
63			list_del_rcu(&thread->links);
64			found_it = true;
65			break;
66		}
67	}
68	spin_unlock(&registry->lock);
69
70	VDO_ASSERT_LOG_ONLY(found_it, "thread found in registry");
71	if (found_it) {
72		/* Ensure no RCU iterators see it before re-initializing. */
73		synchronize_rcu();
74		INIT_LIST_HEAD(&thread->links);
75	}
76}
77
78const void *vdo_lookup_thread(struct thread_registry *registry)
79{
80	struct registered_thread *thread;
81	const void *result = NULL;
82
83	rcu_read_lock();
84	list_for_each_entry_rcu(thread, &registry->links, links) {
85		if (thread->task == current) {
86			result = thread->pointer;
87			break;
88		}
89	}
90	rcu_read_unlock();
91
92	return result;
93}