Commit | Line | Data |
---|---|---|
b2441318 | 1 | // SPDX-License-Identifier: GPL-2.0 |
1366c37e MW |
2 | /* |
3 | * Regression1 | |
4 | * Description: | |
5 | * Salman Qazi describes the following radix-tree bug: | |
6 | * | |
7 | * In the following case, we get can get a deadlock: | |
8 | * | |
9 | * 0. The radix tree contains two items, one has the index 0. | |
10 | * 1. The reader (in this case find_get_pages) takes the rcu_read_lock. | |
11 | * 2. The reader acquires slot(s) for item(s) including the index 0 item. | |
12 | * 3. The non-zero index item is deleted, and as a consequence the other item | |
13 | * is moved to the root of the tree. The place where it used to be is queued | |
14 | * for deletion after the readers finish. | |
15 | * 3b. The zero item is deleted, removing it from the direct slot, it remains in | |
16 | * the rcu-delayed indirect node. | |
17 | * 4. The reader looks at the index 0 slot, and finds that the page has 0 ref | |
18 | * count | |
19 | * 5. The reader looks at it again, hoping that the item will either be freed | |
20 | * or the ref count will increase. This never happens, as the slot it is | |
21 | * looking at will never be updated. Also, this slot can never be reclaimed | |
22 | * because the reader is holding rcu_read_lock and is in an infinite loop. | |
23 | * | |
24 | * The fix is to re-use the same "indirect" pointer case that requires a slot | |
25 | * lookup retry into a general "retry the lookup" bit. | |
26 | * | |
27 | * Running: | |
28 | * This test should run to completion in a few seconds. The above bug would | |
29 | * cause it to hang indefinitely. | |
30 | * | |
31 | * Upstream commit: | |
32 | * Not yet | |
33 | */ | |
34 | #include <linux/kernel.h> | |
35 | #include <linux/gfp.h> | |
36 | #include <linux/slab.h> | |
37 | #include <linux/radix-tree.h> | |
38 | #include <linux/rcupdate.h> | |
39 | #include <stdlib.h> | |
40 | #include <pthread.h> | |
41 | #include <stdio.h> | |
42 | #include <assert.h> | |
43 | ||
44 | #include "regression.h" | |
45 | ||
46 | static RADIX_TREE(mt_tree, GFP_KERNEL); | |
1366c37e MW |
47 | |
48 | struct page { | |
49 | pthread_mutex_t lock; | |
50 | struct rcu_head rcu; | |
51 | int count; | |
52 | unsigned long index; | |
53 | }; | |
54 | ||
a332125f | 55 | static struct page *page_alloc(int index) |
1366c37e MW |
56 | { |
57 | struct page *p; | |
58 | p = malloc(sizeof(struct page)); | |
59 | p->count = 1; | |
a332125f | 60 | p->index = index; |
1366c37e MW |
61 | pthread_mutex_init(&p->lock, NULL); |
62 | ||
63 | return p; | |
64 | } | |
65 | ||
66 | static void page_rcu_free(struct rcu_head *rcu) | |
67 | { | |
68 | struct page *p = container_of(rcu, struct page, rcu); | |
69 | assert(!p->count); | |
70 | pthread_mutex_destroy(&p->lock); | |
71 | free(p); | |
72 | } | |
73 | ||
74 | static void page_free(struct page *p) | |
75 | { | |
76 | call_rcu(&p->rcu, page_rcu_free); | |
77 | } | |
78 | ||
79 | static unsigned find_get_pages(unsigned long start, | |
80 | unsigned int nr_pages, struct page **pages) | |
81 | { | |
a332125f MW |
82 | XA_STATE(xas, &mt_tree, start); |
83 | struct page *page; | |
84 | unsigned int ret = 0; | |
1366c37e MW |
85 | |
86 | rcu_read_lock(); | |
a332125f MW |
87 | xas_for_each(&xas, page, ULONG_MAX) { |
88 | if (xas_retry(&xas, page)) | |
1366c37e MW |
89 | continue; |
90 | ||
1366c37e | 91 | pthread_mutex_lock(&page->lock); |
a332125f MW |
92 | if (!page->count) |
93 | goto unlock; | |
94 | ||
1366c37e MW |
95 | /* don't actually update page refcount */ |
96 | pthread_mutex_unlock(&page->lock); | |
97 | ||
98 | /* Has the page moved? */ | |
a332125f MW |
99 | if (unlikely(page != xas_reload(&xas))) |
100 | goto put_page; | |
1366c37e MW |
101 | |
102 | pages[ret] = page; | |
103 | ret++; | |
a332125f MW |
104 | continue; |
105 | unlock: | |
106 | pthread_mutex_unlock(&page->lock); | |
107 | put_page: | |
108 | xas_reset(&xas); | |
1366c37e MW |
109 | } |
110 | rcu_read_unlock(); | |
111 | return ret; | |
112 | } | |
113 | ||
114 | static pthread_barrier_t worker_barrier; | |
115 | ||
116 | static void *regression1_fn(void *arg) | |
117 | { | |
118 | rcu_register_thread(); | |
119 | ||
120 | if (pthread_barrier_wait(&worker_barrier) == | |
121 | PTHREAD_BARRIER_SERIAL_THREAD) { | |
122 | int j; | |
123 | ||
124 | for (j = 0; j < 1000000; j++) { | |
125 | struct page *p; | |
126 | ||
a332125f | 127 | p = page_alloc(0); |
372266ba | 128 | xa_lock(&mt_tree); |
1366c37e | 129 | radix_tree_insert(&mt_tree, 0, p); |
372266ba | 130 | xa_unlock(&mt_tree); |
1366c37e | 131 | |
a332125f | 132 | p = page_alloc(1); |
372266ba | 133 | xa_lock(&mt_tree); |
1366c37e | 134 | radix_tree_insert(&mt_tree, 1, p); |
372266ba | 135 | xa_unlock(&mt_tree); |
1366c37e | 136 | |
372266ba | 137 | xa_lock(&mt_tree); |
1366c37e MW |
138 | p = radix_tree_delete(&mt_tree, 1); |
139 | pthread_mutex_lock(&p->lock); | |
140 | p->count--; | |
141 | pthread_mutex_unlock(&p->lock); | |
372266ba | 142 | xa_unlock(&mt_tree); |
1366c37e MW |
143 | page_free(p); |
144 | ||
372266ba | 145 | xa_lock(&mt_tree); |
1366c37e MW |
146 | p = radix_tree_delete(&mt_tree, 0); |
147 | pthread_mutex_lock(&p->lock); | |
148 | p->count--; | |
149 | pthread_mutex_unlock(&p->lock); | |
372266ba | 150 | xa_unlock(&mt_tree); |
1366c37e MW |
151 | page_free(p); |
152 | } | |
153 | } else { | |
154 | int j; | |
155 | ||
156 | for (j = 0; j < 100000000; j++) { | |
157 | struct page *pages[10]; | |
158 | ||
159 | find_get_pages(0, 10, pages); | |
160 | } | |
161 | } | |
162 | ||
163 | rcu_unregister_thread(); | |
164 | ||
165 | return NULL; | |
166 | } | |
167 | ||
168 | static pthread_t *threads; | |
169 | void regression1_test(void) | |
170 | { | |
171 | int nr_threads; | |
172 | int i; | |
173 | long arg; | |
174 | ||
175 | /* Regression #1 */ | |
73bc029b | 176 | printv(1, "running regression test 1, should finish in under a minute\n"); |
1366c37e MW |
177 | nr_threads = 2; |
178 | pthread_barrier_init(&worker_barrier, NULL, nr_threads); | |
179 | ||
cac7ea57 | 180 | threads = malloc(nr_threads * sizeof(*threads)); |
1366c37e MW |
181 | |
182 | for (i = 0; i < nr_threads; i++) { | |
183 | arg = i; | |
184 | if (pthread_create(&threads[i], NULL, regression1_fn, (void *)arg)) { | |
185 | perror("pthread_create"); | |
186 | exit(1); | |
187 | } | |
188 | } | |
189 | ||
190 | for (i = 0; i < nr_threads; i++) { | |
191 | if (pthread_join(threads[i], NULL)) { | |
192 | perror("pthread_join"); | |
193 | exit(1); | |
194 | } | |
195 | } | |
196 | ||
197 | free(threads); | |
198 | ||
73bc029b | 199 | printv(1, "regression test 1, done\n"); |
1366c37e | 200 | } |