WebSVN – HelenOS-historic – Diff – /kernel/trunk/generic/src/synch/futex.c

 /*
  * Copyright (C) 2006 Jakub Jermar
  * All rights reserved.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
+ *
  * - Redistributions of source code must retain the above copyright
  *   notice, this list of conditions and the following disclaimer.
  * - Redistributions in binary form must reproduce the above copyright
  *   notice, this list of conditions and the following disclaimer in the
  *   documentation and/or other materials provided with the distribution.
  * - The name of the author may not be used to endorse or promote products
  *   derived from this software without specific prior written permission.
+ *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 /**
  * Kernel backend for futexes.
  * Deallocation of orphaned kernel-side futex structures is not currently implemented.
  */
 #include <synch/futex.h>
 #include <synch/rwlock.h>
 #include <synch/spinlock.h>
 #include <synch/synch.h>
 #include <mm/frame.h>
 #include <mm/page.h>
 #include <mm/slab.h>
 #include <proc/thread.h>
 #include <genarch/mm/page_pt.h>
 #include <genarch/mm/page_ht.h>
 #include <adt/hash_table.h>
 #include <adt/list.h>
 #include <arch.h>
 #include <align.h>
 #include <panic.h>
 #include <errno.h>
 #include <print.h>
 #define FUTEX_HT_SIZE   1024    /* keep it a power of 2 */
 static void futex_initialize(futex_t *futex);
+static futex_t *futex_find(__address paddr);
 static index_t futex_ht_hash(__native *key);
 static bool futex_ht_compare(__native *key, count_t keys, link_t *item);
 static void futex_ht_remove_callback(link_t *item);
 /** Read-write lock protecting global futex hash table. */
 static rwlock_t futex_ht_lock;
 /** Futex hash table. */
 static hash_table_t futex_ht;
 /** Futex hash table operations. */
 static hash_table_operations_t futex_ht_ops = {
     .hash = futex_ht_hash,
     .compare = futex_ht_compare,
     .remove_callback = futex_ht_remove_callback
 };
 /** Initialize futex subsystem. */
 void futex_init(void)
+{
     rwlock_initialize(&futex_ht_lock);
     hash_table_create(&futex_ht, FUTEX_HT_SIZE, 1, &futex_ht_ops);
+}
 /** Initialize kernel futex structure.
+ *
  * @param futex Kernel futex structure.
  */
 void futex_initialize(futex_t *futex)
+{
     waitq_initialize(&futex->wq);
     link_initialize(&futex->ht_link);
     futex->paddr = 0;
+}
 /** Sleep in futex wait queue.
+ *
  * @param uaddr Userspace address of the futex counter.
  * @param usec If non-zero, number of microseconds this thread is willing to sleep.
  * @param trydown If usec is zero and trydown is non-zero, conditional operation will be attempted.
+ *
  * @return One of ESYNCH_TIMEOUT, ESYNCH_OK_ATOMIC and ESYNCH_OK_BLOCKED. See synch.h.
  *     If there is no physical mapping for uaddr ENOENT is returned.
  */
 __native sys_futex_sleep_timeout(__address uaddr, __u32 usec, int trydown)
+{
     futex_t *futex;
     __address paddr;
-    link_t *item;
     pte_t *t;
     ipl_t ipl;
     ipl = interrupts_disable();
     /*
      * Find physical address of futex counter.
      */
     page_table_lock(AS, true);
     t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));
     if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {
         page_table_unlock(AS, true);
         interrupts_restore(ipl);
         return (__native) ENOENT;
+    }
     paddr = PFN2ADDR(PTE_GET_FRAME(t)) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));
     page_table_unlock(AS, true);
     interrupts_restore(ipl);
-    /*
-     * Find the respective futex structure
-     * or allocate new one if it does not exist already.
-     */
-    rwlock_read_lock(&futex_ht_lock);
-    item = hash_table_find(&futex_ht, &paddr);
-    if (item) {
-        futex = hash_table_get_instance(item, futex_t, ht_link);
-        rwlock_read_unlock(&futex_ht_lock);
-    } else {
-        /*
-         * Upgrade to writer is not currently supported,
-         * Therefore, it is necessary to release the read lock
-         * and reacquire it as a writer.
-         */
-        rwlock_read_unlock(&futex_ht_lock);
-        rwlock_write_lock(&futex_ht_lock);
-        /*
-         * Detect possible race condition by searching
-         * the hash table once again with write access.
-         */
-        item = hash_table_find(&futex_ht, &paddr);
-        if (item) {
-            futex = hash_table_get_instance(item, futex_t, ht_link);
-            rwlock_write_unlock(&futex_ht_lock);
-        } else {
-            futex = (futex_t *) malloc(sizeof(futex_t), 0);
-            futex_initialize(futex);
-            futex->paddr = paddr;
+    futex = futex_find(paddr);
-            hash_table_insert(&futex_ht, &paddr, &futex->ht_link);
-            rwlock_write_unlock(&futex_ht_lock);
-        }
-    }
     return (__native) waitq_sleep_timeout(&futex->wq, usec, trydown);
+}
 /** Wakeup one thread waiting in futex wait queue.
+ *
  * @param uaddr Userspace address of the futex counter.
+ *
  * @return ENOENT if there is no futex associated with the address
  *     or if there is no physical mapping for uaddr.
  */
 __native sys_futex_wakeup(__address uaddr)
+{
-    futex_t *futex = NULL;
+    futex_t *futex;
     __address paddr;
-    link_t *item;
     pte_t *t;
     ipl_t ipl;
     ipl = interrupts_disable();
     /*
      * Find physical address of futex counter.
      */
     page_table_lock(AS, true);
     t = page_mapping_find(AS, ALIGN_DOWN(uaddr, PAGE_SIZE));
     if (!t || !PTE_VALID(t) || !PTE_PRESENT(t)) {
         page_table_unlock(AS, true);
         interrupts_restore(ipl);
         return (__native) ENOENT;
+    }
     paddr = PFN2ADDR(PTE_GET_FRAME(t)) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));
     page_table_unlock(AS, true);
     interrupts_restore(ipl);
+    futex = futex_find(paddr);
+    waitq_wakeup(&futex->wq, WAKEUP_FIRST);
+    return 0;
+}
+/** Find kernel address of the futex structure corresponding to paddr.
+ *
+ * If the structure does not exist alreay, a new one is created.
+ *
+ * @param paddr Physical address of the userspace futex counter.
+ *
+ * @return Address of the kernel futex structure.
+ */
+futex_t *futex_find(__address paddr)
+{
+    link_t *item;
+    futex_t *futex;
     /*
-     * Find the respective futex structure.
+     * Find the respective futex structure
+     * or allocate new one if it does not exist already.
      */
     rwlock_read_lock(&futex_ht_lock);
     item = hash_table_find(&futex_ht, &paddr);
     if (item) {
         futex = hash_table_get_instance(item, futex_t, ht_link);
+        rwlock_read_unlock(&futex_ht_lock);
+    } else {
-    }
+        /*
+         * Upgrade to writer is not currently supported,
+         * Therefore, it is necessary to release the read lock
+         * and reacquire it as a writer.
+         */
-    rwlock_read_unlock(&futex_ht_lock);
+        rwlock_read_unlock(&futex_ht_lock);
+        rwlock_write_lock(&futex_ht_lock);
+        /*
+         * Avoid possible race condition by searching
+         * the hash table once again with write access.
+         */
+        item = hash_table_find(&futex_ht, &paddr);
-    if (!futex)
+        if (item) {
+            futex = hash_table_get_instance(item, futex_t, ht_link);
+            rwlock_write_unlock(&futex_ht_lock);
+        } else {
+            futex = (futex_t *) malloc(sizeof(futex_t), 0);
-        return (__native) ENOENT;
+            futex_initialize(futex);
+            futex->paddr = paddr;
+            hash_table_insert(&futex_ht, &paddr, &futex->ht_link);
+            rwlock_write_unlock(&futex_ht_lock);
+        }
-    waitq_wakeup(&futex->wq, WAKEUP_FIRST);
+    }
-    return 0;
+    return futex;
+}
 /** Compute hash index into futex hash table.
+ *
  * @param key Address where the key (i.e. physical address of futex counter) is stored.
+ *
  * @return Index into futex hash table.
  */
 index_t futex_ht_hash(__native *key)
+{
     return *key & (FUTEX_HT_SIZE-1);
+}
 /** Compare futex hash table item with a key.
+ *
  * @param key Address where the key (i.e. physical address of futex counter) is stored.
+ *
  * @return True if the item matches the key. False otherwise.
  */
 bool futex_ht_compare(__native *key, count_t keys, link_t *item)
+{
     futex_t *futex;
     ASSERT(keys == 1);
     futex = hash_table_get_instance(item, futex_t, ht_link);
     return *key == futex->paddr;
+}
 /** Callback for removal items from futex hash table.
+ *
  * @param item Item removed from the hash table.
  */
 void futex_ht_remove_callback(link_t *item)
+{
     futex_t *futex;
     futex = hash_table_get_instance(item, futex_t, ht_link);
     free(futex);
+}

Subversion Repositories HelenOS-historic

(root)/kernel/trunk/generic/src/synch/futex.c – Rev 1117 → 1153