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
vdo_initialize_thread_registry(struct thread_registry * registry)18 void vdo_initialize_thread_registry(struct thread_registry *registry)
19 {
20 INIT_LIST_HEAD(®istry->links);
21 spin_lock_init(®istry->lock);
22 }
23
24 /* Register the current thread and associate it with a data pointer. */
vdo_register_thread(struct thread_registry * registry,struct registered_thread * new_thread,const void * pointer)25 void 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(®istry->lock);
36 list_for_each_entry(thread, ®istry->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, ®istry->links);
45 spin_unlock(®istry->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
vdo_unregister_thread(struct thread_registry * registry)55 void vdo_unregister_thread(struct thread_registry *registry)
56 {
57 struct registered_thread *thread;
58 bool found_it = false;
59
60 spin_lock(®istry->lock);
61 list_for_each_entry(thread, ®istry->links, links) {
62 if (thread->task == current) {
63 list_del_rcu(&thread->links);
64 found_it = true;
65 break;
66 }
67 }
68 spin_unlock(®istry->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
vdo_lookup_thread(struct thread_registry * registry)78 const 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, ®istry->links, links) {
85 if (thread->task == current) {
86 result = thread->pointer;
87 break;
88 }
89 }
90 rcu_read_unlock();
91
92 return result;
93 }
94