1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
|
/*
* Regression1
* Description:
* Salman Qazi describes the following radix-tree bug:
*
* In the following case, we get can get a deadlock:
*
* 0. The radix tree contains two items, one has the index 0.
* 1. The reader (in this case find_get_pages) takes the rcu_read_lock.
* 2. The reader acquires slot(s) for item(s) including the index 0 item.
* 3. The non-zero index item is deleted, and as a consequence the other item
* is moved to the root of the tree. The place where it used to be is queued
* for deletion after the readers finish.
* 3b. The zero item is deleted, removing it from the direct slot, it remains in
* the rcu-delayed indirect node.
* 4. The reader looks at the index 0 slot, and finds that the page has 0 ref
* count
* 5. The reader looks at it again, hoping that the item will either be freed
* or the ref count will increase. This never happens, as the slot it is
* looking at will never be updated. Also, this slot can never be reclaimed
* because the reader is holding rcu_read_lock and is in an infinite loop.
*
* The fix is to re-use the same "indirect" pointer case that requires a slot
* lookup retry into a general "retry the lookup" bit.
*
* Running:
* This test should run to completion in a few seconds. The above bug would
* cause it to hang indefinitely.
*
* Upstream commit:
* Not yet
*/
#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/slab.h>
#include <linux/radix-tree.h>
#include <linux/rcupdate.h>
#include <stdlib.h>
#include <pthread.h>
#include <stdio.h>
#include <assert.h>
#include "regression.h"
static RADIX_TREE(mt_tree, GFP_KERNEL);
static pthread_mutex_t mt_lock = PTHREAD_MUTEX_INITIALIZER;
struct page {
pthread_mutex_t lock;
struct rcu_head rcu;
int count;
unsigned long index;
};
static struct page *page_alloc(void)
{
struct page *p;
p = malloc(sizeof(struct page));
p->count = 1;
p->index = 1;
pthread_mutex_init(&p->lock, NULL);
return p;
}
static void page_rcu_free(struct rcu_head *rcu)
{
struct page *p = container_of(rcu, struct page, rcu);
assert(!p->count);
pthread_mutex_destroy(&p->lock);
free(p);
}
static void page_free(struct page *p)
{
call_rcu(&p->rcu, page_rcu_free);
}
static unsigned find_get_pages(unsigned long start,
unsigned int nr_pages, struct page **pages)
{
unsigned int i;
unsigned int ret;
unsigned int nr_found;
rcu_read_lock();
restart:
nr_found = radix_tree_gang_lookup_slot(&mt_tree,
(void ***)pages, NULL, start, nr_pages);
ret = 0;
for (i = 0; i < nr_found; i++) {
struct page *page;
repeat:
page = radix_tree_deref_slot((void **)pages[i]);
if (unlikely(!page))
continue;
if (radix_tree_exception(page)) {
if (radix_tree_deref_retry(page)) {
/*
* Transient condition which can only trigger
* when entry at index 0 moves out of or back
* to root: none yet gotten, safe to restart.
*/
assert((start | i) == 0);
goto restart;
}
/*
* No exceptional entries are inserted in this test.
*/
assert(0);
}
pthread_mutex_lock(&page->lock);
if (!page->count) {
pthread_mutex_unlock(&page->lock);
goto repeat;
}
/* don't actually update page refcount */
pthread_mutex_unlock(&page->lock);
/* Has the page moved? */
if (unlikely(page != *((void **)pages[i]))) {
goto repeat;
}
pages[ret] = page;
ret++;
}
rcu_read_unlock();
return ret;
}
static pthread_barrier_t worker_barrier;
static void *regression1_fn(void *arg)
{
rcu_register_thread();
if (pthread_barrier_wait(&worker_barrier) ==
PTHREAD_BARRIER_SERIAL_THREAD) {
int j;
for (j = 0; j < 1000000; j++) {
struct page *p;
p = page_alloc();
pthread_mutex_lock(&mt_lock);
radix_tree_insert(&mt_tree, 0, p);
pthread_mutex_unlock(&mt_lock);
p = page_alloc();
pthread_mutex_lock(&mt_lock);
radix_tree_insert(&mt_tree, 1, p);
pthread_mutex_unlock(&mt_lock);
pthread_mutex_lock(&mt_lock);
p = radix_tree_delete(&mt_tree, 1);
pthread_mutex_lock(&p->lock);
p->count--;
pthread_mutex_unlock(&p->lock);
pthread_mutex_unlock(&mt_lock);
page_free(p);
pthread_mutex_lock(&mt_lock);
p = radix_tree_delete(&mt_tree, 0);
pthread_mutex_lock(&p->lock);
p->count--;
pthread_mutex_unlock(&p->lock);
pthread_mutex_unlock(&mt_lock);
page_free(p);
}
} else {
int j;
for (j = 0; j < 100000000; j++) {
struct page *pages[10];
find_get_pages(0, 10, pages);
}
}
rcu_unregister_thread();
return NULL;
}
static pthread_t *threads;
void regression1_test(void)
{
int nr_threads;
int i;
long arg;
/* Regression #1 */
printv(1, "running regression test 1, should finish in under a minute\n");
nr_threads = 2;
pthread_barrier_init(&worker_barrier, NULL, nr_threads);
threads = malloc(nr_threads * sizeof(pthread_t *));
for (i = 0; i < nr_threads; i++) {
arg = i;
if (pthread_create(&threads[i], NULL, regression1_fn, (void *)arg)) {
perror("pthread_create");
exit(1);
}
}
for (i = 0; i < nr_threads; i++) {
if (pthread_join(threads[i], NULL)) {
perror("pthread_join");
exit(1);
}
}
free(threads);
printv(1, "regression test 1, done\n");
}
|
