1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (C) 2018 HUAWEI, Inc.
4 * https://www.huawei.com/
5 */
6 #include "internal.h"
7 #include <linux/pagevec.h>
8
erofs_allocpage(struct page ** pagepool,gfp_t gfp)9 struct page *erofs_allocpage(struct page **pagepool, gfp_t gfp)
10 {
11 struct page *page = *pagepool;
12
13 if (page) {
14 DBG_BUGON(page_ref_count(page) != 1);
15 *pagepool = (struct page *)page_private(page);
16 } else {
17 page = alloc_page(gfp);
18 }
19 return page;
20 }
21
erofs_release_pages(struct page ** pagepool)22 void erofs_release_pages(struct page **pagepool)
23 {
24 while (*pagepool) {
25 struct page *page = *pagepool;
26
27 *pagepool = (struct page *)page_private(page);
28 put_page(page);
29 }
30 }
31
32 #ifdef CONFIG_EROFS_FS_ZIP
33 /* global shrink count (for all mounted EROFS instances) */
34 static atomic_long_t erofs_global_shrink_cnt;
35
erofs_workgroup_get(struct erofs_workgroup * grp)36 static int erofs_workgroup_get(struct erofs_workgroup *grp)
37 {
38 int o;
39
40 repeat:
41 o = erofs_wait_on_workgroup_freezed(grp);
42 if (o <= 0)
43 return -1;
44
45 if (atomic_cmpxchg(&grp->refcount, o, o + 1) != o)
46 goto repeat;
47
48 /* decrease refcount paired by erofs_workgroup_put */
49 if (o == 1)
50 atomic_long_dec(&erofs_global_shrink_cnt);
51 return 0;
52 }
53
erofs_find_workgroup(struct super_block * sb,pgoff_t index)54 struct erofs_workgroup *erofs_find_workgroup(struct super_block *sb,
55 pgoff_t index)
56 {
57 struct erofs_sb_info *sbi = EROFS_SB(sb);
58 struct erofs_workgroup *grp;
59
60 repeat:
61 rcu_read_lock();
62 grp = xa_load(&sbi->managed_pslots, index);
63 if (grp) {
64 if (erofs_workgroup_get(grp)) {
65 /* prefer to relax rcu read side */
66 rcu_read_unlock();
67 goto repeat;
68 }
69
70 DBG_BUGON(index != grp->index);
71 }
72 rcu_read_unlock();
73 return grp;
74 }
75
erofs_insert_workgroup(struct super_block * sb,struct erofs_workgroup * grp)76 struct erofs_workgroup *erofs_insert_workgroup(struct super_block *sb,
77 struct erofs_workgroup *grp)
78 {
79 struct erofs_sb_info *const sbi = EROFS_SB(sb);
80 struct erofs_workgroup *pre;
81
82 /*
83 * Bump up a reference count before making this visible
84 * to others for the XArray in order to avoid potential
85 * UAF without serialized by xa_lock.
86 */
87 atomic_inc(&grp->refcount);
88
89 repeat:
90 xa_lock(&sbi->managed_pslots);
91 pre = __xa_cmpxchg(&sbi->managed_pslots, grp->index,
92 NULL, grp, GFP_NOFS);
93 if (pre) {
94 if (xa_is_err(pre)) {
95 pre = ERR_PTR(xa_err(pre));
96 } else if (erofs_workgroup_get(pre)) {
97 /* try to legitimize the current in-tree one */
98 xa_unlock(&sbi->managed_pslots);
99 cond_resched();
100 goto repeat;
101 }
102 atomic_dec(&grp->refcount);
103 grp = pre;
104 }
105 xa_unlock(&sbi->managed_pslots);
106 return grp;
107 }
108
__erofs_workgroup_free(struct erofs_workgroup * grp)109 static void __erofs_workgroup_free(struct erofs_workgroup *grp)
110 {
111 atomic_long_dec(&erofs_global_shrink_cnt);
112 erofs_workgroup_free_rcu(grp);
113 }
114
erofs_workgroup_put(struct erofs_workgroup * grp)115 int erofs_workgroup_put(struct erofs_workgroup *grp)
116 {
117 int count = atomic_dec_return(&grp->refcount);
118
119 if (count == 1)
120 atomic_long_inc(&erofs_global_shrink_cnt);
121 else if (!count)
122 __erofs_workgroup_free(grp);
123 return count;
124 }
125
erofs_try_to_release_workgroup(struct erofs_sb_info * sbi,struct erofs_workgroup * grp)126 static bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
127 struct erofs_workgroup *grp)
128 {
129 /*
130 * If managed cache is on, refcount of workgroups
131 * themselves could be < 0 (freezed). In other words,
132 * there is no guarantee that all refcounts > 0.
133 */
134 if (!erofs_workgroup_try_to_freeze(grp, 1))
135 return false;
136
137 /*
138 * Note that all cached pages should be unattached
139 * before deleted from the XArray. Otherwise some
140 * cached pages could be still attached to the orphan
141 * old workgroup when the new one is available in the tree.
142 */
143 if (erofs_try_to_free_all_cached_pages(sbi, grp)) {
144 erofs_workgroup_unfreeze(grp, 1);
145 return false;
146 }
147
148 /*
149 * It's impossible to fail after the workgroup is freezed,
150 * however in order to avoid some race conditions, add a
151 * DBG_BUGON to observe this in advance.
152 */
153 DBG_BUGON(__xa_erase(&sbi->managed_pslots, grp->index) != grp);
154
155 /* last refcount should be connected with its managed pslot. */
156 erofs_workgroup_unfreeze(grp, 0);
157 __erofs_workgroup_free(grp);
158 return true;
159 }
160
erofs_shrink_workstation(struct erofs_sb_info * sbi,unsigned long nr_shrink)161 static unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
162 unsigned long nr_shrink)
163 {
164 struct erofs_workgroup *grp;
165 unsigned int freed = 0;
166 unsigned long index;
167
168 xa_lock(&sbi->managed_pslots);
169 xa_for_each(&sbi->managed_pslots, index, grp) {
170 /* try to shrink each valid workgroup */
171 if (!erofs_try_to_release_workgroup(sbi, grp))
172 continue;
173 xa_unlock(&sbi->managed_pslots);
174
175 ++freed;
176 if (!--nr_shrink)
177 return freed;
178 xa_lock(&sbi->managed_pslots);
179 }
180 xa_unlock(&sbi->managed_pslots);
181 return freed;
182 }
183
184 /* protected by 'erofs_sb_list_lock' */
185 static unsigned int shrinker_run_no;
186
187 /* protects the mounted 'erofs_sb_list' */
188 static DEFINE_SPINLOCK(erofs_sb_list_lock);
189 static LIST_HEAD(erofs_sb_list);
190
erofs_shrinker_register(struct super_block * sb)191 void erofs_shrinker_register(struct super_block *sb)
192 {
193 struct erofs_sb_info *sbi = EROFS_SB(sb);
194
195 mutex_init(&sbi->umount_mutex);
196
197 spin_lock(&erofs_sb_list_lock);
198 list_add(&sbi->list, &erofs_sb_list);
199 spin_unlock(&erofs_sb_list_lock);
200 }
201
erofs_shrinker_unregister(struct super_block * sb)202 void erofs_shrinker_unregister(struct super_block *sb)
203 {
204 struct erofs_sb_info *const sbi = EROFS_SB(sb);
205
206 mutex_lock(&sbi->umount_mutex);
207 /* clean up all remaining workgroups in memory */
208 erofs_shrink_workstation(sbi, ~0UL);
209
210 spin_lock(&erofs_sb_list_lock);
211 list_del(&sbi->list);
212 spin_unlock(&erofs_sb_list_lock);
213 mutex_unlock(&sbi->umount_mutex);
214 }
215
erofs_shrink_count(struct shrinker * shrink,struct shrink_control * sc)216 static unsigned long erofs_shrink_count(struct shrinker *shrink,
217 struct shrink_control *sc)
218 {
219 return atomic_long_read(&erofs_global_shrink_cnt);
220 }
221
erofs_shrink_scan(struct shrinker * shrink,struct shrink_control * sc)222 static unsigned long erofs_shrink_scan(struct shrinker *shrink,
223 struct shrink_control *sc)
224 {
225 struct erofs_sb_info *sbi;
226 struct list_head *p;
227
228 unsigned long nr = sc->nr_to_scan;
229 unsigned int run_no;
230 unsigned long freed = 0;
231
232 spin_lock(&erofs_sb_list_lock);
233 do {
234 run_no = ++shrinker_run_no;
235 } while (run_no == 0);
236
237 /* Iterate over all mounted superblocks and try to shrink them */
238 p = erofs_sb_list.next;
239 while (p != &erofs_sb_list) {
240 sbi = list_entry(p, struct erofs_sb_info, list);
241
242 /*
243 * We move the ones we do to the end of the list, so we stop
244 * when we see one we have already done.
245 */
246 if (sbi->shrinker_run_no == run_no)
247 break;
248
249 if (!mutex_trylock(&sbi->umount_mutex)) {
250 p = p->next;
251 continue;
252 }
253
254 spin_unlock(&erofs_sb_list_lock);
255 sbi->shrinker_run_no = run_no;
256
257 freed += erofs_shrink_workstation(sbi, nr - freed);
258
259 spin_lock(&erofs_sb_list_lock);
260 /* Get the next list element before we move this one */
261 p = p->next;
262
263 /*
264 * Move this one to the end of the list to provide some
265 * fairness.
266 */
267 list_move_tail(&sbi->list, &erofs_sb_list);
268 mutex_unlock(&sbi->umount_mutex);
269
270 if (freed >= nr)
271 break;
272 }
273 spin_unlock(&erofs_sb_list_lock);
274 return freed;
275 }
276
277 static struct shrinker erofs_shrinker_info = {
278 .scan_objects = erofs_shrink_scan,
279 .count_objects = erofs_shrink_count,
280 .seeks = DEFAULT_SEEKS,
281 };
282
erofs_init_shrinker(void)283 int __init erofs_init_shrinker(void)
284 {
285 return register_shrinker(&erofs_shrinker_info);
286 }
287
erofs_exit_shrinker(void)288 void erofs_exit_shrinker(void)
289 {
290 unregister_shrinker(&erofs_shrinker_info);
291 }
292 #endif /* !CONFIG_EROFS_FS_ZIP */
293