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1109 jermar 1
/*
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 * Copyright (C) 2006 Jakub Jermar
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 * All rights reserved.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 *
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 * - Redistributions of source code must retain the above copyright
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 *   notice, this list of conditions and the following disclaimer.
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 * - Redistributions in binary form must reproduce the above copyright
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 *   notice, this list of conditions and the following disclaimer in the
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 *   documentation and/or other materials provided with the distribution.
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 * - The name of the author may not be used to endorse or promote products
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 *   derived from this software without specific prior written permission.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */
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/**
1264 jermar 30
 * @file    futex.c
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 * @brief   Kernel backend for futexes.
1109 jermar 32
 */
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34
#include <synch/futex.h>
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#include <synch/rwlock.h>
1117 jermar 36
#include <synch/spinlock.h>
1109 jermar 37
#include <synch/synch.h>
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#include <mm/frame.h>
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#include <mm/page.h>
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#include <mm/slab.h>
1117 jermar 41
#include <proc/thread.h>
1460 jermar 42
#include <proc/task.h>
1109 jermar 43
#include <genarch/mm/page_pt.h>
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#include <genarch/mm/page_ht.h>
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#include <adt/hash_table.h>
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#include <adt/list.h>
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#include <arch.h>
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#include <align.h>
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#include <panic.h>
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#include <errno.h>
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#include <print.h>
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#define FUTEX_HT_SIZE   1024    /* keep it a power of 2 */
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55
static void futex_initialize(futex_t *futex);
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1153 jermar 57
static futex_t *futex_find(__address paddr);
1109 jermar 58
static index_t futex_ht_hash(__native *key);
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static bool futex_ht_compare(__native *key, count_t keys, link_t *item);
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static void futex_ht_remove_callback(link_t *item);
61
 
1460 jermar 62
/**
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 * Read-write lock protecting global futex hash table.
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 * It is also used to serialize access to all futex_t structures.
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 * Must be acquired before the task futex B+tree lock.
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 */
1109 jermar 67
static rwlock_t futex_ht_lock;
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69
/** Futex hash table. */
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static hash_table_t futex_ht;
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72
/** Futex hash table operations. */
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static hash_table_operations_t futex_ht_ops = {
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    .hash = futex_ht_hash,
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    .compare = futex_ht_compare,
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    .remove_callback = futex_ht_remove_callback
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};
78
 
79
/** Initialize futex subsystem. */
80
void futex_init(void)
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{
82
    rwlock_initialize(&futex_ht_lock);
83
    hash_table_create(&futex_ht, FUTEX_HT_SIZE, 1, &futex_ht_ops);
84
}
85
 
86
/** Initialize kernel futex structure.
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 *
88
 * @param futex Kernel futex structure.
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 */
90
void futex_initialize(futex_t *futex)
91
{
92
    waitq_initialize(&futex->wq);
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    link_initialize(&futex->ht_link);
94
    futex->paddr = 0;
1460 jermar 95
    futex->refcount = 1;
1109 jermar 96
}
97
 
98
/** Sleep in futex wait queue.
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 *
100
 * @param uaddr Userspace address of the futex counter.
1117 jermar 101
 * @param usec If non-zero, number of microseconds this thread is willing to sleep.
1502 jermar 102
 * @param flags Select mode of operation.
1109 jermar 103
 *
1117 jermar 104
 * @return One of ESYNCH_TIMEOUT, ESYNCH_OK_ATOMIC and ESYNCH_OK_BLOCKED. See synch.h.
1109 jermar 105
 *     If there is no physical mapping for uaddr ENOENT is returned.
106
 */
1502 jermar 107
__native sys_futex_sleep_timeout(__address uaddr, __u32 usec, int flags)
1109 jermar 108
{
109
    futex_t *futex;
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    __address paddr;
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    pte_t *t;
1117 jermar 112
    ipl_t ipl;
1109 jermar 113
 
1117 jermar 114
    ipl = interrupts_disable();
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1109 jermar 116
    /*
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     * Find physical address of futex counter.
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     */
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    page_table_lock(AS, true);
120
    t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));
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    if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {
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        page_table_unlock(AS, true);
1117 jermar 123
        interrupts_restore(ipl);
1109 jermar 124
        return (__native) ENOENT;
125
    }
1414 jermar 126
    paddr = PTE_GET_FRAME(t) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));
1109 jermar 127
    page_table_unlock(AS, true);
128
 
1117 jermar 129
    interrupts_restore(ipl);   
130
 
1153 jermar 131
    futex = futex_find(paddr);
1109 jermar 132
 
1502 jermar 133
    return (__native) waitq_sleep_timeout(&futex->wq, usec, flags | SYNCH_FLAGS_INTERRUPTIBLE);
1109 jermar 134
}
135
 
136
/** Wakeup one thread waiting in futex wait queue.
137
 *
138
 * @param uaddr Userspace address of the futex counter.
139
 *
1414 jermar 140
 * @return ENOENT if there is no physical mapping for uaddr.
1109 jermar 141
 */
142
__native sys_futex_wakeup(__address uaddr)
143
{
1153 jermar 144
    futex_t *futex;
1109 jermar 145
    __address paddr;
146
    pte_t *t;
1117 jermar 147
    ipl_t ipl;
1109 jermar 148
 
1117 jermar 149
    ipl = interrupts_disable();
150
 
1109 jermar 151
    /*
152
     * Find physical address of futex counter.
153
     */
154
    page_table_lock(AS, true);
155
    t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));
156
    if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {
157
        page_table_unlock(AS, true);
1117 jermar 158
        interrupts_restore(ipl);
1109 jermar 159
        return (__native) ENOENT;
160
    }
1414 jermar 161
    paddr = PTE_GET_FRAME(t) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));
1109 jermar 162
    page_table_unlock(AS, true);
163
 
1117 jermar 164
    interrupts_restore(ipl);
165
 
1153 jermar 166
    futex = futex_find(paddr);
167
 
168
    waitq_wakeup(&futex->wq, WAKEUP_FIRST);
169
 
170
    return 0;
171
}
172
 
173
/** Find kernel address of the futex structure corresponding to paddr.
174
 *
1460 jermar 175
 * If the structure does not exist already, a new one is created.
1153 jermar 176
 *
177
 * @param paddr Physical address of the userspace futex counter.
178
 *
179
 * @return Address of the kernel futex structure.
180
 */
181
futex_t *futex_find(__address paddr)
182
{
183
    link_t *item;
184
    futex_t *futex;
1460 jermar 185
    btree_node_t *leaf;
1153 jermar 186
 
1109 jermar 187
    /*
1153 jermar 188
     * Find the respective futex structure
189
     * or allocate new one if it does not exist already.
1109 jermar 190
     */
191
    rwlock_read_lock(&futex_ht_lock);
192
    item = hash_table_find(&futex_ht, &paddr);
193
    if (item) {
194
        futex = hash_table_get_instance(item, futex_t, ht_link);
1460 jermar 195
 
196
        /*
197
         * See if the current task knows this futex.
198
         */
199
        mutex_lock(&TASK->futexes_lock);
200
        if (!btree_search(&TASK->futexes, paddr, &leaf)) {
201
            /*
202
             * The futex is new to the current task.
203
             * However, we only have read access.
204
             * Gain write access and try again.
205
             */
206
            mutex_unlock(&TASK->futexes_lock);
207
            goto gain_write_access;
208
        }
209
        mutex_unlock(&TASK->futexes_lock);
210
 
1153 jermar 211
        rwlock_read_unlock(&futex_ht_lock);
212
    } else {
1460 jermar 213
gain_write_access:
1153 jermar 214
        /*
215
         * Upgrade to writer is not currently supported,
1414 jermar 216
         * therefore, it is necessary to release the read lock
1153 jermar 217
         * and reacquire it as a writer.
218
         */
219
        rwlock_read_unlock(&futex_ht_lock);
220
 
221
        rwlock_write_lock(&futex_ht_lock);
222
        /*
223
         * Avoid possible race condition by searching
224
         * the hash table once again with write access.
225
         */
226
        item = hash_table_find(&futex_ht, &paddr);
227
        if (item) {
228
            futex = hash_table_get_instance(item, futex_t, ht_link);
1460 jermar 229
 
230
            /*
231
             * See if this futex is known to the current task.
232
             */
233
            mutex_lock(&TASK->futexes_lock);
234
            if (!btree_search(&TASK->futexes, paddr, &leaf)) {
235
                /*
236
                 * The futex is new to the current task.
237
                 * Upgrade its reference count and put it to the
238
                 * current task's B+tree of known futexes.
239
                 */
240
                futex->refcount++;
241
                btree_insert(&TASK->futexes, paddr, futex, leaf);
242
            }
243
            mutex_unlock(&TASK->futexes_lock);
244
 
1153 jermar 245
            rwlock_write_unlock(&futex_ht_lock);
246
        } else {
247
            futex = (futex_t *) malloc(sizeof(futex_t), 0);
248
            futex_initialize(futex);
249
            futex->paddr = paddr;
250
            hash_table_insert(&futex_ht, &paddr, &futex->ht_link);
1460 jermar 251
 
252
            /*
253
             * This is the first task referencing the futex.
254
             * It can be directly inserted into its
255
             * B+tree of known futexes.
256
             */
257
            mutex_lock(&TASK->futexes_lock);
258
            btree_insert(&TASK->futexes, paddr, futex, NULL);
259
            mutex_unlock(&TASK->futexes_lock);
260
 
1153 jermar 261
            rwlock_write_unlock(&futex_ht_lock);
262
        }
1109 jermar 263
    }
264
 
1153 jermar 265
    return futex;
1109 jermar 266
}
267
 
268
/** Compute hash index into futex hash table.
269
 *
1248 jermar 270
 * @param key Address where the key (i.e. physical address of futex counter) is stored.
1109 jermar 271
 *
272
 * @return Index into futex hash table.
273
 */
274
index_t futex_ht_hash(__native *key)
275
{
276
    return *key & (FUTEX_HT_SIZE-1);
277
}
278
 
279
/** Compare futex hash table item with a key.
280
 *
281
 * @param key Address where the key (i.e. physical address of futex counter) is stored.
282
 *
1248 jermar 283
 * @return True if the item matches the key. False otherwise.
1109 jermar 284
 */
285
bool futex_ht_compare(__native *key, count_t keys, link_t *item)
286
{
287
    futex_t *futex;
288
 
289
    ASSERT(keys == 1);
290
 
291
    futex = hash_table_get_instance(item, futex_t, ht_link);
292
    return *key == futex->paddr;
293
}
294
 
295
/** Callback for removal items from futex hash table.
296
 *
297
 * @param item Item removed from the hash table.
298
 */
299
void futex_ht_remove_callback(link_t *item)
300
{
301
    futex_t *futex;
302
 
303
    futex = hash_table_get_instance(item, futex_t, ht_link);
304
    free(futex);
305
}
1583 jermar 306
 
307
/** Remove references from futexes known to the current task. */
308
void futex_cleanup(void)
309
{
1586 jermar 310
    link_t *cur;
311
 
312
    rwlock_write_lock(&futex_ht_lock);
313
    mutex_lock(&TASK->futexes_lock);
314
 
315
    for (cur = TASK->futexes.leaf_head.next; cur != &TASK->futexes.leaf_head; cur = cur->next) {
316
        btree_node_t *node;
317
        int i;
318
 
319
        node = list_get_instance(cur, btree_node_t, leaf_link);
320
        for (i = 0; i < node->keys; i++) {
321
            futex_t *ftx;
322
            __address paddr = node->key[i];
323
 
324
            ftx = (futex_t *) node->value[i];
325
            if (--ftx->refcount == 0)
326
                hash_table_remove(&futex_ht, &paddr, 1);
327
        }
328
    }
329
 
330
    mutex_unlock(&TASK->futexes_lock);
331
    rwlock_write_unlock(&futex_ht_lock);
1583 jermar 332
}