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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 futex_t *futex_find(__address paddr);
  57. static index_t futex_ht_hash(__native *key);
  58. static bool futex_ht_compare(__native *key, count_t keys, link_t *item);
  59. static void futex_ht_remove_callback(link_t *item);
  60.  
  61. /** Read-write lock protecting global futex hash table. */
  62. static rwlock_t futex_ht_lock;
  63.  
  64. /** Futex hash table. */
  65. static hash_table_t futex_ht;
  66.  
  67. /** Futex hash table operations. */
  68. static hash_table_operations_t futex_ht_ops = {
  69.     .hash = futex_ht_hash,
  70.     .compare = futex_ht_compare,
  71.     .remove_callback = futex_ht_remove_callback
  72. };
  73.  
  74. /** Initialize futex subsystem. */
  75. void futex_init(void)
  76. {
  77.     rwlock_initialize(&futex_ht_lock);
  78.     hash_table_create(&futex_ht, FUTEX_HT_SIZE, 1, &futex_ht_ops);
  79. }
  80.  
  81. /** Initialize kernel futex structure.
  82.  *
  83.  * @param futex Kernel futex structure.
  84.  */
  85. void futex_initialize(futex_t *futex)
  86. {
  87.     waitq_initialize(&futex->wq);
  88.     link_initialize(&futex->ht_link);
  89.     futex->paddr = 0;
  90. }
  91.  
  92. /** Sleep in futex wait queue.
  93.  *
  94.  * @param uaddr Userspace address of the futex counter.
  95.  * @param usec If non-zero, number of microseconds this thread is willing to sleep.
  96.  * @param trydown If usec is zero and trydown is non-zero, conditional operation will be attempted.
  97.  *
  98.  * @return One of ESYNCH_TIMEOUT, ESYNCH_OK_ATOMIC and ESYNCH_OK_BLOCKED. See synch.h.
  99.  *     If there is no physical mapping for uaddr ENOENT is returned.
  100.  */
  101. __native sys_futex_sleep_timeout(__address uaddr, __u32 usec, int trydown)
  102. {
  103.     futex_t *futex;
  104.     __address paddr;
  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.     futex = futex_find(paddr);
  126.    
  127.     return (__native) waitq_sleep_timeout(&futex->wq, usec, trydown);
  128. }
  129.  
  130. /** Wakeup one thread waiting in futex wait queue.
  131.  *
  132.  * @param uaddr Userspace address of the futex counter.
  133.  *
  134.  * @return ENOENT if there is no futex associated with the address
  135.  *     or if there is no physical mapping for uaddr.
  136.  */
  137. __native sys_futex_wakeup(__address uaddr)
  138. {
  139.     futex_t *futex;
  140.     __address paddr;
  141.     pte_t *t;
  142.     ipl_t ipl;
  143.    
  144.     ipl = interrupts_disable();
  145.    
  146.     /*
  147.      * Find physical address of futex counter.
  148.      */
  149.     page_table_lock(AS, true);
  150.     t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));
  151.     if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {
  152.         page_table_unlock(AS, true);
  153.         interrupts_restore(ipl);
  154.         return (__native) ENOENT;
  155.     }
  156.     paddr = PFN2ADDR(PTE_GET_FRAME(t)) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));
  157.     page_table_unlock(AS, true);
  158.    
  159.     interrupts_restore(ipl);
  160.  
  161.     futex = futex_find(paddr);
  162.        
  163.     waitq_wakeup(&futex->wq, WAKEUP_FIRST);
  164.    
  165.     return 0;
  166. }
  167.  
  168. /** Find kernel address of the futex structure corresponding to paddr.
  169.  *
  170.  * If the structure does not exist alreay, a new one is created.
  171.  *
  172.  * @param paddr Physical address of the userspace futex counter.
  173.  *
  174.  * @return Address of the kernel futex structure.
  175.  */
  176. futex_t *futex_find(__address paddr)
  177. {
  178.     link_t *item;
  179.     futex_t *futex;
  180.    
  181.     /*
  182.      * Find the respective futex structure
  183.      * or allocate new one if it does not exist already.
  184.      */
  185.     rwlock_read_lock(&futex_ht_lock);
  186.     item = hash_table_find(&futex_ht, &paddr);
  187.     if (item) {
  188.         futex = hash_table_get_instance(item, futex_t, ht_link);
  189.         rwlock_read_unlock(&futex_ht_lock);
  190.     } else {
  191.         /*
  192.          * Upgrade to writer is not currently supported,
  193.          * Therefore, it is necessary to release the read lock
  194.          * and reacquire it as a writer.
  195.          */
  196.         rwlock_read_unlock(&futex_ht_lock);
  197.  
  198.         rwlock_write_lock(&futex_ht_lock);
  199.         /*
  200.          * Avoid possible race condition by searching
  201.          * the hash table once again with write access.
  202.          */
  203.         item = hash_table_find(&futex_ht, &paddr);
  204.         if (item) {
  205.             futex = hash_table_get_instance(item, futex_t, ht_link);
  206.             rwlock_write_unlock(&futex_ht_lock);
  207.         } else {
  208.             futex = (futex_t *) malloc(sizeof(futex_t), 0);
  209.             futex_initialize(futex);
  210.             futex->paddr = paddr;
  211.             hash_table_insert(&futex_ht, &paddr, &futex->ht_link);
  212.             rwlock_write_unlock(&futex_ht_lock);
  213.         }
  214.     }
  215.    
  216.     return futex;
  217. }
  218.  
  219. /** Compute hash index into futex hash table.
  220.  *
  221.  * @param key Address where the key (i.e. physical address of futex counter) is stored.
  222.  *
  223.  * @return Index into futex hash table.
  224.  */
  225. index_t futex_ht_hash(__native *key)
  226. {
  227.     return *key & (FUTEX_HT_SIZE-1);
  228. }
  229.  
  230. /** Compare futex hash table item with a key.
  231.  *
  232.  * @param key Address where the key (i.e. physical address of futex counter) is stored.
  233.  *
  234.  * @return True if the item matches the key. False otherwise.
  235.  */
  236. bool futex_ht_compare(__native *key, count_t keys, link_t *item)
  237. {
  238.     futex_t *futex;
  239.  
  240.     ASSERT(keys == 1);
  241.  
  242.     futex = hash_table_get_instance(item, futex_t, ht_link);
  243.     return *key == futex->paddr;
  244. }
  245.  
  246. /** Callback for removal items from futex hash table.
  247.  *
  248.  * @param item Item removed from the hash table.
  249.  */
  250. void futex_ht_remove_callback(link_t *item)
  251. {
  252.     futex_t *futex;
  253.  
  254.     futex = hash_table_get_instance(item, futex_t, ht_link);
  255.     free(futex);
  256. }
  257.