xref: /freebsd/sys/contrib/openzfs/module/zfs/refcount.c (revision 924226fba12cc9a228c73b956e1b7fa24c60b055)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
23  * Copyright (c) 2012, 2021 by Delphix. All rights reserved.
24  */
25 
26 #include <sys/zfs_context.h>
27 #include <sys/zfs_refcount.h>
28 
29 #ifdef	ZFS_DEBUG
30 /*
31  * Reference count tracking is disabled by default.  It's memory requirements
32  * are reasonable, however as implemented it consumes a significant amount of
33  * cpu time.  Until its performance is improved it should be manually enabled.
34  */
35 int reference_tracking_enable = B_FALSE;
36 static int reference_history = 3; /* tunable */
37 
38 static kmem_cache_t *reference_cache;
39 static kmem_cache_t *reference_history_cache;
40 
41 void
42 zfs_refcount_init(void)
43 {
44 	reference_cache = kmem_cache_create("reference_cache",
45 	    sizeof (reference_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
46 
47 	reference_history_cache = kmem_cache_create("reference_history_cache",
48 	    sizeof (uint64_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
49 }
50 
51 void
52 zfs_refcount_fini(void)
53 {
54 	kmem_cache_destroy(reference_cache);
55 	kmem_cache_destroy(reference_history_cache);
56 }
57 
58 void
59 zfs_refcount_create(zfs_refcount_t *rc)
60 {
61 	mutex_init(&rc->rc_mtx, NULL, MUTEX_DEFAULT, NULL);
62 	list_create(&rc->rc_list, sizeof (reference_t),
63 	    offsetof(reference_t, ref_link));
64 	list_create(&rc->rc_removed, sizeof (reference_t),
65 	    offsetof(reference_t, ref_link));
66 	rc->rc_count = 0;
67 	rc->rc_removed_count = 0;
68 	rc->rc_tracked = reference_tracking_enable;
69 }
70 
71 void
72 zfs_refcount_create_tracked(zfs_refcount_t *rc)
73 {
74 	zfs_refcount_create(rc);
75 	rc->rc_tracked = B_TRUE;
76 }
77 
78 void
79 zfs_refcount_create_untracked(zfs_refcount_t *rc)
80 {
81 	zfs_refcount_create(rc);
82 	rc->rc_tracked = B_FALSE;
83 }
84 
85 void
86 zfs_refcount_destroy_many(zfs_refcount_t *rc, uint64_t number)
87 {
88 	reference_t *ref;
89 
90 	ASSERT3U(rc->rc_count, ==, number);
91 	while ((ref = list_head(&rc->rc_list))) {
92 		list_remove(&rc->rc_list, ref);
93 		kmem_cache_free(reference_cache, ref);
94 	}
95 	list_destroy(&rc->rc_list);
96 
97 	while ((ref = list_head(&rc->rc_removed))) {
98 		list_remove(&rc->rc_removed, ref);
99 		kmem_cache_free(reference_history_cache, ref->ref_removed);
100 		kmem_cache_free(reference_cache, ref);
101 	}
102 	list_destroy(&rc->rc_removed);
103 	mutex_destroy(&rc->rc_mtx);
104 }
105 
106 void
107 zfs_refcount_destroy(zfs_refcount_t *rc)
108 {
109 	zfs_refcount_destroy_many(rc, 0);
110 }
111 
112 int
113 zfs_refcount_is_zero(zfs_refcount_t *rc)
114 {
115 	return (zfs_refcount_count(rc) == 0);
116 }
117 
118 int64_t
119 zfs_refcount_count(zfs_refcount_t *rc)
120 {
121 	return (atomic_load_64(&rc->rc_count));
122 }
123 
124 int64_t
125 zfs_refcount_add_many(zfs_refcount_t *rc, uint64_t number, const void *holder)
126 {
127 	reference_t *ref = NULL;
128 	int64_t count;
129 
130 	if (!rc->rc_tracked) {
131 		count = atomic_add_64_nv(&(rc)->rc_count, number);
132 		ASSERT3U(count, >=, number);
133 		return (count);
134 	}
135 
136 	ref = kmem_cache_alloc(reference_cache, KM_SLEEP);
137 	ref->ref_holder = holder;
138 	ref->ref_number = number;
139 	mutex_enter(&rc->rc_mtx);
140 	ASSERT3U(rc->rc_count, >=, 0);
141 	list_insert_head(&rc->rc_list, ref);
142 	rc->rc_count += number;
143 	count = rc->rc_count;
144 	mutex_exit(&rc->rc_mtx);
145 
146 	return (count);
147 }
148 
149 int64_t
150 zfs_refcount_add(zfs_refcount_t *rc, const void *holder)
151 {
152 	return (zfs_refcount_add_many(rc, 1, holder));
153 }
154 
155 int64_t
156 zfs_refcount_remove_many(zfs_refcount_t *rc, uint64_t number,
157     const void *holder)
158 {
159 	reference_t *ref;
160 	int64_t count;
161 
162 	if (!rc->rc_tracked) {
163 		count = atomic_add_64_nv(&(rc)->rc_count, -number);
164 		ASSERT3S(count, >=, 0);
165 		return (count);
166 	}
167 
168 	mutex_enter(&rc->rc_mtx);
169 	ASSERT3U(rc->rc_count, >=, number);
170 	for (ref = list_head(&rc->rc_list); ref;
171 	    ref = list_next(&rc->rc_list, ref)) {
172 		if (ref->ref_holder == holder && ref->ref_number == number) {
173 			list_remove(&rc->rc_list, ref);
174 			if (reference_history > 0) {
175 				ref->ref_removed =
176 				    kmem_cache_alloc(reference_history_cache,
177 				    KM_SLEEP);
178 				list_insert_head(&rc->rc_removed, ref);
179 				rc->rc_removed_count++;
180 				if (rc->rc_removed_count > reference_history) {
181 					ref = list_tail(&rc->rc_removed);
182 					list_remove(&rc->rc_removed, ref);
183 					kmem_cache_free(reference_history_cache,
184 					    ref->ref_removed);
185 					kmem_cache_free(reference_cache, ref);
186 					rc->rc_removed_count--;
187 				}
188 			} else {
189 				kmem_cache_free(reference_cache, ref);
190 			}
191 			rc->rc_count -= number;
192 			count = rc->rc_count;
193 			mutex_exit(&rc->rc_mtx);
194 			return (count);
195 		}
196 	}
197 	panic("No such hold %p on refcount %llx", holder,
198 	    (u_longlong_t)(uintptr_t)rc);
199 	return (-1);
200 }
201 
202 int64_t
203 zfs_refcount_remove(zfs_refcount_t *rc, const void *holder)
204 {
205 	return (zfs_refcount_remove_many(rc, 1, holder));
206 }
207 
208 void
209 zfs_refcount_transfer(zfs_refcount_t *dst, zfs_refcount_t *src)
210 {
211 	int64_t count, removed_count;
212 	list_t list, removed;
213 
214 	list_create(&list, sizeof (reference_t),
215 	    offsetof(reference_t, ref_link));
216 	list_create(&removed, sizeof (reference_t),
217 	    offsetof(reference_t, ref_link));
218 
219 	mutex_enter(&src->rc_mtx);
220 	count = src->rc_count;
221 	removed_count = src->rc_removed_count;
222 	src->rc_count = 0;
223 	src->rc_removed_count = 0;
224 	list_move_tail(&list, &src->rc_list);
225 	list_move_tail(&removed, &src->rc_removed);
226 	mutex_exit(&src->rc_mtx);
227 
228 	mutex_enter(&dst->rc_mtx);
229 	dst->rc_count += count;
230 	dst->rc_removed_count += removed_count;
231 	list_move_tail(&dst->rc_list, &list);
232 	list_move_tail(&dst->rc_removed, &removed);
233 	mutex_exit(&dst->rc_mtx);
234 
235 	list_destroy(&list);
236 	list_destroy(&removed);
237 }
238 
239 void
240 zfs_refcount_transfer_ownership_many(zfs_refcount_t *rc, uint64_t number,
241     const void *current_holder, const void *new_holder)
242 {
243 	reference_t *ref;
244 	boolean_t found = B_FALSE;
245 
246 	if (!rc->rc_tracked)
247 		return;
248 
249 	mutex_enter(&rc->rc_mtx);
250 	for (ref = list_head(&rc->rc_list); ref;
251 	    ref = list_next(&rc->rc_list, ref)) {
252 		if (ref->ref_holder == current_holder &&
253 		    ref->ref_number == number) {
254 			ref->ref_holder = new_holder;
255 			found = B_TRUE;
256 			break;
257 		}
258 	}
259 	ASSERT(found);
260 	mutex_exit(&rc->rc_mtx);
261 }
262 
263 void
264 zfs_refcount_transfer_ownership(zfs_refcount_t *rc, const void *current_holder,
265     const void *new_holder)
266 {
267 	return (zfs_refcount_transfer_ownership_many(rc, 1, current_holder,
268 	    new_holder));
269 }
270 
271 /*
272  * If tracking is enabled, return true if a reference exists that matches
273  * the "holder" tag. If tracking is disabled, then return true if a reference
274  * might be held.
275  */
276 boolean_t
277 zfs_refcount_held(zfs_refcount_t *rc, const void *holder)
278 {
279 	reference_t *ref;
280 
281 	if (!rc->rc_tracked)
282 		return (zfs_refcount_count(rc) > 0);
283 
284 	mutex_enter(&rc->rc_mtx);
285 	for (ref = list_head(&rc->rc_list); ref;
286 	    ref = list_next(&rc->rc_list, ref)) {
287 		if (ref->ref_holder == holder) {
288 			mutex_exit(&rc->rc_mtx);
289 			return (B_TRUE);
290 		}
291 	}
292 	mutex_exit(&rc->rc_mtx);
293 	return (B_FALSE);
294 }
295 
296 /*
297  * If tracking is enabled, return true if a reference does not exist that
298  * matches the "holder" tag. If tracking is disabled, always return true
299  * since the reference might not be held.
300  */
301 boolean_t
302 zfs_refcount_not_held(zfs_refcount_t *rc, const void *holder)
303 {
304 	reference_t *ref;
305 
306 	if (!rc->rc_tracked)
307 		return (B_TRUE);
308 
309 	mutex_enter(&rc->rc_mtx);
310 	for (ref = list_head(&rc->rc_list); ref;
311 	    ref = list_next(&rc->rc_list, ref)) {
312 		if (ref->ref_holder == holder) {
313 			mutex_exit(&rc->rc_mtx);
314 			return (B_FALSE);
315 		}
316 	}
317 	mutex_exit(&rc->rc_mtx);
318 	return (B_TRUE);
319 }
320 
321 EXPORT_SYMBOL(zfs_refcount_create);
322 EXPORT_SYMBOL(zfs_refcount_destroy);
323 EXPORT_SYMBOL(zfs_refcount_is_zero);
324 EXPORT_SYMBOL(zfs_refcount_count);
325 EXPORT_SYMBOL(zfs_refcount_add);
326 EXPORT_SYMBOL(zfs_refcount_remove);
327 EXPORT_SYMBOL(zfs_refcount_held);
328 
329 /* BEGIN CSTYLED */
330 ZFS_MODULE_PARAM(zfs, , reference_tracking_enable, INT, ZMOD_RW,
331 	"Track reference holders to refcount_t objects");
332 
333 ZFS_MODULE_PARAM(zfs, , reference_history, INT, ZMOD_RW,
334 	"Maximum reference holders being tracked");
335 /* END CSTYLED */
336 #endif	/* ZFS_DEBUG */
337