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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. /**
  30.  * Kernel backend for futexes.
  31.  * Deallocation of orphaned kernel-side futex structures is not currently implemented.
  32.  */
  33.  
  34. #include <synch/futex.h>
  35. #include <synch/rwlock.h>
  36. #include <synch/spinlock.h>
  37. #include <synch/synch.h>
  38. #include <mm/frame.h>
  39. #include <mm/page.h>
  40. #include <mm/slab.h>
  41. #include <proc/thread.h>
  42. #include <genarch/mm/page_pt.h>
  43. #include <genarch/mm/page_ht.h>
  44. #include <adt/hash_table.h>
  45. #include <adt/list.h>
  46. #include <arch.h>
  47. #include <align.h>
  48. #include <panic.h>
  49. #include <errno.h>
  50. #include <print.h>
  51.  
  52. #define FUTEX_HT_SIZE   1024    /* keep it a power of 2 */
  53.  
  54. static void futex_initialize(futex_t *futex);
  55.  
  56. static index_t futex_ht_hash(__native *key);
  57. static bool futex_ht_compare(__native *key, count_t keys, link_t *item);
  58. static void futex_ht_remove_callback(link_t *item);
  59.  
  60. /** Read-write lock protecting global futex hash table. */
  61. static rwlock_t futex_ht_lock;
  62.  
  63. /** Futex hash table. */
  64. static hash_table_t futex_ht;
  65.  
  66. /** Futex hash table operations. */
  67. static hash_table_operations_t futex_ht_ops = {
  68.     .hash = futex_ht_hash,
  69.     .compare = futex_ht_compare,
  70.     .remove_callback = futex_ht_remove_callback
  71. };
  72.  
  73. /** Initialize futex subsystem. */
  74. void futex_init(void)
  75. {
  76.     rwlock_initialize(&futex_ht_lock);
  77.     hash_table_create(&futex_ht, FUTEX_HT_SIZE, 1, &futex_ht_ops);
  78. }
  79.  
  80. /** Initialize kernel futex structure.
  81.  *
  82.  * @param futex Kernel futex structure.
  83.  */
  84. void futex_initialize(futex_t *futex)
  85. {
  86.     waitq_initialize(&futex->wq);
  87.     link_initialize(&futex->ht_link);
  88.     futex->paddr = 0;
  89. }
  90.  
  91. /** Sleep in futex wait queue.
  92.  *
  93.  * @param uaddr Userspace address of the futex counter.
  94.  * @param usec If non-zero, number of microseconds this thread is willing to sleep.
  95.  * @param trydown If usec is zero and trydown is non-zero, conditional operation will be attempted.
  96.  *
  97.  * @return One of ESYNCH_TIMEOUT, ESYNCH_OK_ATOMIC and ESYNCH_OK_BLOCKED. See synch.h.
  98.  *     If there is no physical mapping for uaddr ENOENT is returned.
  99.  */
  100. __native sys_futex_sleep_timeout(__address uaddr, __u32 usec, int trydown)
  101. {
  102.     futex_t *futex;
  103.     __address paddr;
  104.     link_t *item;
  105.     pte_t *t;
  106.     ipl_t ipl;
  107.    
  108.     ipl = interrupts_disable();
  109.  
  110.     /*
  111.      * Find physical address of futex counter.
  112.      */
  113.     page_table_lock(AS, true);
  114.     t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));
  115.     if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {
  116.         page_table_unlock(AS, true);
  117.         interrupts_restore(ipl);
  118.         return (__native) ENOENT;
  119.     }
  120.     paddr = PFN2ADDR(PTE_GET_FRAME(t)) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));
  121.     page_table_unlock(AS, true);
  122.    
  123.     interrupts_restore(ipl);   
  124.  
  125.     /*
  126.      * Find the respective futex structure
  127.      * or allocate new one if it does not exist already.
  128.      */
  129.     rwlock_read_lock(&futex_ht_lock);
  130.     item = hash_table_find(&futex_ht, &paddr);
  131.     if (item) {
  132.         futex = hash_table_get_instance(item, futex_t, ht_link);
  133.         rwlock_read_unlock(&futex_ht_lock);
  134.     } else {
  135.         /*
  136.          * Upgrade to writer is not currently supported,
  137.          * Therefore, it is necessary to release the read lock
  138.          * and reacquire it as a writer.
  139.          */
  140.         rwlock_read_unlock(&futex_ht_lock);
  141.  
  142.         rwlock_write_lock(&futex_ht_lock);
  143.         /*
  144.          * Detect possible race condition by searching
  145.          * the hash table once again with write access.
  146.          */
  147.         item = hash_table_find(&futex_ht, &paddr);
  148.         if (item) {
  149.             futex = hash_table_get_instance(item, futex_t, ht_link);
  150.             rwlock_write_unlock(&futex_ht_lock);
  151.         } else {
  152.             futex = (futex_t *) malloc(sizeof(futex_t), 0);
  153.             futex_initialize(futex);
  154.             futex->paddr = paddr;
  155.             hash_table_insert(&futex_ht, &paddr, &futex->ht_link);
  156.             rwlock_write_unlock(&futex_ht_lock);
  157.         }
  158.     }
  159.    
  160.     return (__native) waitq_sleep_timeout(&futex->wq, usec, trydown);
  161. }
  162.  
  163. /** Wakeup one thread waiting in futex wait queue.
  164.  *
  165.  * @param uaddr Userspace address of the futex counter.
  166.  *
  167.  * @return ENOENT if there is no futex associated with the address
  168.  *     or if there is no physical mapping for uaddr.
  169.  */
  170. __native sys_futex_wakeup(__address uaddr)
  171. {
  172.     futex_t *futex = NULL;
  173.     __address paddr;
  174.     link_t *item;
  175.     pte_t *t;
  176.     ipl_t ipl;
  177.    
  178.     ipl = interrupts_disable();
  179.    
  180.     /*
  181.      * Find physical address of futex counter.
  182.      */
  183.     page_table_lock(AS, true);
  184.     t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));
  185.     if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {
  186.         page_table_unlock(AS, true);
  187.         interrupts_restore(ipl);
  188.         return (__native) ENOENT;
  189.     }
  190.     paddr = PFN2ADDR(PTE_GET_FRAME(t)) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));
  191.     page_table_unlock(AS, true);
  192.    
  193.     interrupts_restore(ipl);
  194.  
  195.     /*
  196.      * Find the respective futex structure.
  197.      */
  198.     rwlock_read_lock(&futex_ht_lock);
  199.     item = hash_table_find(&futex_ht, &paddr);
  200.     if (item) {
  201.         futex = hash_table_get_instance(item, futex_t, ht_link);
  202.     }
  203.     rwlock_read_unlock(&futex_ht_lock);
  204.  
  205.     if (!futex)
  206.         return (__native) ENOENT;  
  207.        
  208.     waitq_wakeup(&futex->wq, WAKEUP_FIRST);
  209.    
  210.     return 0;
  211. }
  212.  
  213. /** Compute hash index into futex hash table.
  214.  *
  215.  * @param key Address where the key (i.e. physical address of futex counter) is stored.
  216.  *
  217.  * @return Index into futex hash table.
  218.  */
  219. index_t futex_ht_hash(__native *key)
  220. {
  221.     return *key & (FUTEX_HT_SIZE-1);
  222. }
  223.  
  224. /** Compare futex hash table item with a key.
  225.  *
  226.  * @param key Address where the key (i.e. physical address of futex counter) is stored.
  227.  *
  228.  * @return True if the item matches the key. False otherwise.
  229.  */
  230. bool futex_ht_compare(__native *key, count_t keys, link_t *item)
  231. {
  232.     futex_t *futex;
  233.  
  234.     ASSERT(keys == 1);
  235.  
  236.     futex = hash_table_get_instance(item, futex_t, ht_link);
  237.     return *key == futex->paddr;
  238. }
  239.  
  240. /** Callback for removal items from futex hash table.
  241.  *
  242.  * @param item Item removed from the hash table.
  243.  */
  244. void futex_ht_remove_callback(link_t *item)
  245. {
  246.     futex_t *futex;
  247.  
  248.     futex = hash_table_get_instance(item, futex_t, ht_link);
  249.     free(futex);
  250. }
  251.