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  1. /*
  2.  * Copyright (c) 2006 Jakub Jermar
  3.  * All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions
  7.  * are met:
  8.  *
  9.  * - Redistributions of source code must retain the above copyright
  10.  *   notice, this list of conditions and the following disclaimer.
  11.  * - Redistributions in binary form must reproduce the above copyright
  12.  *   notice, this list of conditions and the following disclaimer in the
  13.  *   documentation and/or other materials provided with the distribution.
  14.  * - The name of the author may not be used to endorse or promote products
  15.  *   derived from this software without specific prior written permission.
  16.  *
  17.  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18.  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19.  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20.  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21.  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22.  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23.  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24.  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25.  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26.  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27.  */
  28.  
  29. /** @addtogroup sync
  30.  * @{
  31.  */
  32.  
  33. /**
  34.  * @file
  35.  * @brief   Kernel backend for futexes.
  36.  */
  37.  
  38. #include <synch/futex.h>
  39. #include <synch/rwlock.h>
  40. #include <synch/spinlock.h>
  41. #include <synch/synch.h>
  42. #include <mm/frame.h>
  43. #include <mm/page.h>
  44. #include <mm/slab.h>
  45. #include <proc/thread.h>
  46. #include <proc/task.h>
  47. #include <genarch/mm/page_pt.h>
  48. #include <genarch/mm/page_ht.h>
  49. #include <adt/hash_table.h>
  50. #include <adt/list.h>
  51. #include <arch.h>
  52. #include <align.h>
  53. #include <panic.h>
  54. #include <errno.h>
  55. #include <print.h>
  56.  
  57. #define FUTEX_HT_SIZE   1024    /* keep it a power of 2 */
  58.  
  59. static void futex_initialize(futex_t *futex);
  60.  
  61. static futex_t *futex_find(uintptr_t paddr);
  62. static index_t futex_ht_hash(unative_t *key);
  63. static bool futex_ht_compare(unative_t *key, count_t keys, link_t *item);
  64. static void futex_ht_remove_callback(link_t *item);
  65.  
  66. /**
  67.  * Read-write lock protecting global futex hash table.
  68.  * It is also used to serialize access to all futex_t structures.
  69.  * Must be acquired before the task futex B+tree lock.
  70.  */
  71. static rwlock_t futex_ht_lock;
  72.  
  73. /** Futex hash table. */
  74. static hash_table_t futex_ht;
  75.  
  76. /** Futex hash table operations. */
  77. static hash_table_operations_t futex_ht_ops = {
  78.     .hash = futex_ht_hash,
  79.     .compare = futex_ht_compare,
  80.     .remove_callback = futex_ht_remove_callback
  81. };
  82.  
  83. /** Initialize futex subsystem. */
  84. void futex_init(void)
  85. {
  86.     rwlock_initialize(&futex_ht_lock);
  87.     hash_table_create(&futex_ht, FUTEX_HT_SIZE, 1, &futex_ht_ops);
  88. }
  89.  
  90. /** Initialize kernel futex structure.
  91.  *
  92.  * @param futex Kernel futex structure.
  93.  */
  94. void futex_initialize(futex_t *futex)
  95. {
  96.     waitq_initialize(&futex->wq);
  97.     link_initialize(&futex->ht_link);
  98.     futex->paddr = 0;
  99.     futex->refcount = 1;
  100. }
  101.  
  102. /** Sleep in futex wait queue.
  103.  *
  104.  * @param uaddr Userspace address of the futex counter.
  105.  * @param usec If non-zero, number of microseconds this thread is willing to
  106.  *     sleep.
  107.  * @param flags Select mode of operation.
  108.  *
  109.  * @return One of ESYNCH_TIMEOUT, ESYNCH_OK_ATOMIC and ESYNCH_OK_BLOCKED. See
  110.  *     synch.h. If there is no physical mapping for uaddr ENOENT is returned.
  111.  */
  112. unative_t sys_futex_sleep_timeout(uintptr_t uaddr, uint32_t usec, int flags)
  113. {
  114.     futex_t *futex;
  115.     uintptr_t paddr;
  116.     pte_t *t;
  117.     ipl_t ipl;
  118.     int rc;
  119.    
  120.     ipl = interrupts_disable();
  121.  
  122.     /*
  123.      * Find physical address of futex counter.
  124.      */
  125.     page_table_lock(AS, true);
  126.     t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));
  127.     if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {
  128.         page_table_unlock(AS, true);
  129.         interrupts_restore(ipl);
  130.         return (unative_t) ENOENT;
  131.     }
  132.     paddr = PTE_GET_FRAME(t) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));
  133.     page_table_unlock(AS, true);
  134.    
  135.     interrupts_restore(ipl);   
  136.  
  137.     futex = futex_find(paddr);
  138.  
  139. #ifdef CONFIG_UDEBUG
  140.     udebug_stoppable_begin();
  141. #endif
  142.     rc = waitq_sleep_timeout(&futex->wq, usec, flags |
  143.         SYNCH_FLAGS_INTERRUPTIBLE);
  144.  
  145. #ifdef CONFIG_UDEBUG
  146.     udebug_stoppable_end();
  147. #endif
  148.     return (unative_t) rc;
  149. }
  150.  
  151. /** Wakeup one thread waiting in futex wait queue.
  152.  *
  153.  * @param uaddr Userspace address of the futex counter.
  154.  *
  155.  * @return ENOENT if there is no physical mapping for uaddr.
  156.  */
  157. unative_t sys_futex_wakeup(uintptr_t uaddr)
  158. {
  159.     futex_t *futex;
  160.     uintptr_t paddr;
  161.     pte_t *t;
  162.     ipl_t ipl;
  163.    
  164.     ipl = interrupts_disable();
  165.    
  166.     /*
  167.      * Find physical address of futex counter.
  168.      */
  169.     page_table_lock(AS, true);
  170.     t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));
  171.     if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {
  172.         page_table_unlock(AS, true);
  173.         interrupts_restore(ipl);
  174.         return (unative_t) ENOENT;
  175.     }
  176.     paddr = PTE_GET_FRAME(t) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));
  177.     page_table_unlock(AS, true);
  178.    
  179.     interrupts_restore(ipl);
  180.  
  181.     futex = futex_find(paddr);
  182.        
  183.     waitq_wakeup(&futex->wq, WAKEUP_FIRST);
  184.    
  185.     return 0;
  186. }
  187.  
  188. /** Find kernel address of the futex structure corresponding to paddr.
  189.  *
  190.  * If the structure does not exist already, a new one is created.
  191.  *
  192.  * @param paddr Physical address of the userspace futex counter.
  193.  *
  194.  * @return Address of the kernel futex structure.
  195.  */
  196. futex_t *futex_find(uintptr_t paddr)
  197. {
  198.     link_t *item;
  199.     futex_t *futex;
  200.     btree_node_t *leaf;
  201.    
  202.     /*
  203.      * Find the respective futex structure
  204.      * or allocate new one if it does not exist already.
  205.      */
  206.     rwlock_read_lock(&futex_ht_lock);
  207.     item = hash_table_find(&futex_ht, &paddr);
  208.     if (item) {
  209.         futex = hash_table_get_instance(item, futex_t, ht_link);
  210.  
  211.         /*
  212.          * See if the current task knows this futex.
  213.          */
  214.         mutex_lock(&TASK->futexes_lock);
  215.         if (!btree_search(&TASK->futexes, paddr, &leaf)) {
  216.             /*
  217.              * The futex is new to the current task.
  218.              * However, we only have read access.
  219.              * Gain write access and try again.
  220.              */
  221.             mutex_unlock(&TASK->futexes_lock);
  222.             goto gain_write_access;
  223.         }
  224.         mutex_unlock(&TASK->futexes_lock);
  225.  
  226.         rwlock_read_unlock(&futex_ht_lock);
  227.     } else {
  228. gain_write_access:
  229.         /*
  230.          * Upgrade to writer is not currently supported,
  231.          * therefore, it is necessary to release the read lock
  232.          * and reacquire it as a writer.
  233.          */
  234.         rwlock_read_unlock(&futex_ht_lock);
  235.  
  236.         rwlock_write_lock(&futex_ht_lock);
  237.         /*
  238.          * Avoid possible race condition by searching
  239.          * the hash table once again with write access.
  240.          */
  241.         item = hash_table_find(&futex_ht, &paddr);
  242.         if (item) {
  243.             futex = hash_table_get_instance(item, futex_t, ht_link);
  244.            
  245.             /*
  246.              * See if this futex is known to the current task.
  247.              */
  248.             mutex_lock(&TASK->futexes_lock);
  249.             if (!btree_search(&TASK->futexes, paddr, &leaf)) {
  250.                 /*
  251.                  * The futex is new to the current task.
  252.                  * Upgrade its reference count and put it to the
  253.                  * current task's B+tree of known futexes.
  254.                  */
  255.                 futex->refcount++;
  256.                 btree_insert(&TASK->futexes, paddr, futex,
  257.                     leaf);
  258.             }
  259.             mutex_unlock(&TASK->futexes_lock);
  260.    
  261.             rwlock_write_unlock(&futex_ht_lock);
  262.         } else {
  263.             futex = (futex_t *) malloc(sizeof(futex_t), 0);
  264.             futex_initialize(futex);
  265.             futex->paddr = paddr;
  266.             hash_table_insert(&futex_ht, &paddr, &futex->ht_link);
  267.            
  268.             /*
  269.              * This is the first task referencing the futex.
  270.              * It can be directly inserted into its
  271.              * B+tree of known futexes.
  272.              */
  273.             mutex_lock(&TASK->futexes_lock);
  274.             btree_insert(&TASK->futexes, paddr, futex, NULL);
  275.             mutex_unlock(&TASK->futexes_lock);
  276.            
  277.             rwlock_write_unlock(&futex_ht_lock);
  278.         }
  279.     }
  280.    
  281.     return futex;
  282. }
  283.  
  284. /** Compute hash index into futex hash table.
  285.  *
  286.  * @param key Address where the key (i.e. physical address of futex counter) is
  287.  *     stored.
  288.  *
  289.  * @return Index into futex hash table.
  290.  */
  291. index_t futex_ht_hash(unative_t *key)
  292. {
  293.     return *key & (FUTEX_HT_SIZE-1);
  294. }
  295.  
  296. /** Compare futex hash table item with a key.
  297.  *
  298.  * @param key Address where the key (i.e. physical address of futex counter) is
  299.  *     stored.
  300.  *
  301.  * @return True if the item matches the key. False otherwise.
  302.  */
  303. bool futex_ht_compare(unative_t *key, count_t keys, link_t *item)
  304. {
  305.     futex_t *futex;
  306.  
  307.     ASSERT(keys == 1);
  308.  
  309.     futex = hash_table_get_instance(item, futex_t, ht_link);
  310.     return *key == futex->paddr;
  311. }
  312.  
  313. /** Callback for removal items from futex hash table.
  314.  *
  315.  * @param item Item removed from the hash table.
  316.  */
  317. void futex_ht_remove_callback(link_t *item)
  318. {
  319.     futex_t *futex;
  320.  
  321.     futex = hash_table_get_instance(item, futex_t, ht_link);
  322.     free(futex);
  323. }
  324.  
  325. /** Remove references from futexes known to the current task. */
  326. void futex_cleanup(void)
  327. {
  328.     link_t *cur;
  329.    
  330.     rwlock_write_lock(&futex_ht_lock);
  331.     mutex_lock(&TASK->futexes_lock);
  332.  
  333.     for (cur = TASK->futexes.leaf_head.next;
  334.         cur != &TASK->futexes.leaf_head; cur = cur->next) {
  335.         btree_node_t *node;
  336.         unsigned int i;
  337.        
  338.         node = list_get_instance(cur, btree_node_t, leaf_link);
  339.         for (i = 0; i < node->keys; i++) {
  340.             futex_t *ftx;
  341.             uintptr_t paddr = node->key[i];
  342.            
  343.             ftx = (futex_t *) node->value[i];
  344.             if (--ftx->refcount == 0)
  345.                 hash_table_remove(&futex_ht, &paddr, 1);
  346.         }
  347.     }
  348.    
  349.     mutex_unlock(&TASK->futexes_lock);
  350.     rwlock_write_unlock(&futex_ht_lock);
  351. }
  352.  
  353. /** @}
  354.  */
  355.