/*
* 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 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;
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, trydown);
}
/** 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);
}