xref: /linux/drivers/md/dm-vdo/thread-registry.c (revision 4b660dbd9ee2059850fd30e0df420ca7a38a1856) 
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 
18 void 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. */
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(&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 
55 void 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 
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, &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 }
94