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/*

 * 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.

 */

/**

 * @file    futex.c

 * @brief   Kernel backend for futexes.

 */

#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 <proc/task.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.

 * It is also used to serialize access to all futex_t structures.

 * Must be acquired before the task futex B+tree lock.

 */

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;

    futex->refcount = 1;

}

/** 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 flags Select mode of operation.

 *

 * @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 flags)

{

    futex_t *futex;

    __address paddr;

    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 = PTE_GET_FRAME(t) + (uaddr - ALIGN_DOWN(uaddr, PAGE_SIZE));

    page_table_unlock(AS, true);

    interrupts_restore(ipl);   

    futex = futex_find(paddr);

    return (__native) waitq_sleep_timeout(&futex->wq, usec, flags | SYNCH_FLAGS_INTERRUPTIBLE);

}

/** Wakeup one thread waiting in futex wait queue.

 *

 * @param uaddr Userspace address of the futex counter.

 *

 * @return ENOENT if there is no physical mapping for uaddr.

 */

__native sys_futex_wakeup(__address uaddr)

{

    futex_t *futex;

    __address paddr;

    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 = 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 already, 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;

    btree_node_t *leaf;

    /*

     * 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);

        /*

         * See if the current task knows this futex.

         */

        mutex_lock(&TASK->futexes_lock);

        if (!btree_search(&TASK->futexes, paddr, &leaf)) {

            /*

             * The futex is new to the current task.

             * However, we only have read access.

             * Gain write access and try again.

             */

            mutex_unlock(&TASK->futexes_lock);

            goto gain_write_access;

        }

        mutex_unlock(&TASK->futexes_lock);

        rwlock_read_unlock(&futex_ht_lock);

    } else {

gain_write_access:

        /*

         * 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);

        /*

         * Avoid 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);

            /*

             * See if this futex is known to the current task.

             */

            mutex_lock(&TASK->futexes_lock);

            if (!btree_search(&TASK->futexes, paddr, &leaf)) {

                /*

                 * The futex is new to the current task.

                 * Upgrade its reference count and put it to the

                 * current task's B+tree of known futexes.

                 */

                futex->refcount++;

                btree_insert(&TASK->futexes, paddr, futex, leaf);

            }

            mutex_unlock(&TASK->futexes_lock);

            rwlock_write_unlock(&futex_ht_lock);

        } else {

            futex = (futex_t *) malloc(sizeof(futex_t), 0);

            futex_initialize(futex);

            futex->paddr = paddr;

            hash_table_insert(&futex_ht, &paddr, &futex->ht_link);

            /*

             * This is the first task referencing the futex.

             * It can be directly inserted into its

             * B+tree of known futexes.

             */

            mutex_lock(&TASK->futexes_lock);

            btree_insert(&TASK->futexes, paddr, futex, NULL);

            mutex_unlock(&TASK->futexes_lock);

            rwlock_write_unlock(&futex_ht_lock);

        }

    }

    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);

}

/** Remove references from futexes known to the current task. */

void futex_cleanup(void)

{

    link_t *cur;

    rwlock_write_lock(&futex_ht_lock);

    mutex_lock(&TASK->futexes_lock);

    for (cur = TASK->futexes.leaf_head.next; cur != &TASK->futexes.leaf_head; cur = cur->next) {

        btree_node_t *node;

        int i;

        node = list_get_instance(cur, btree_node_t, leaf_link);

        for (i = 0; i < node->keys; i++) {

            futex_t *ftx;

            __address paddr = node->key[i];

            ftx = (futex_t *) node->value[i];

            if (--ftx->refcount == 0)

                hash_table_remove(&futex_ht, &paddr, 1);

        }

    }

    mutex_unlock(&TASK->futexes_lock);

    rwlock_write_unlock(&futex_ht_lock);

}