--- /dev/null
+#ifndef _LINUX_HASH_H
+#define _LINUX_HASH_H
+/* Fast hashing routine for a long.
+ (C) 2002 William Lee Irwin III, IBM */
+
+/*
+ * Knuth recommends primes in approximately golden ratio to the maximum
+ * integer representable by a machine word for multiplicative hashing.
+ * Chuck Lever verified the effectiveness of this technique:
+ * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
+ *
+ * These primes are chosen to be bit-sparse, that is operations on
+ * them can use shifts and additions instead of multiplications for
+ * machines where multiplications are slow.
+ */
+#if BITS_PER_LONG == 32
+/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
+#define GOLDEN_RATIO_PRIME 0x9e370001UL
+#elif BITS_PER_LONG == 64
+/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
+#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
+#else
+#error Define GOLDEN_RATIO_PRIME for your wordsize.
+#endif
+
+static inline unsigned long hash_long(unsigned long val, unsigned int bits)
+{
+ unsigned long hash = val;
+
+#if BITS_PER_LONG == 64
+ /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
+ unsigned long n = hash;
+ n <<= 18;
+ hash -= n;
+ n <<= 33;
+ hash -= n;
+ n <<= 3;
+ hash += n;
+ n <<= 3;
+ hash -= n;
+ n <<= 4;
+ hash += n;
+ n <<= 2;
+ hash += n;
+#else
+ /* On some cpus multiply is faster, on others gcc will do shifts */
+ hash *= GOLDEN_RATIO_PRIME;
+#endif
+
+ /* High bits are more random, so use them. */
+ return hash >> (BITS_PER_LONG - bits);
+}
+
+static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
+{
+ return hash_long((unsigned long)ptr, bits);
+}
+#endif /* _LINUX_HASH_H */
--- /dev/null
+/*
+ * Fast Userspace Mutexes (which I call "Futexes!").
+ * (C) Rusty Russell, IBM 2002
+ *
+ * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
+ * enough at me, Linus for the original (flawed) idea, Matthew
+ * Kirkwood for proof-of-concept implementation.
+ *
+ * "The futexes are also cursed."
+ * "But they come in a choice of three flavours!"
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+#include <linux/kernel.h>
+#include <linux/spinlock.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/hash.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/futex.h>
+#include <linux/highmem.h>
+#include <asm/atomic.h>
+
+/* These mutexes are a very simple counter: the winner is the one who
+ decrements from 1 to 0. The counter starts at 1 when the lock is
+ free. A value other than 0 or 1 means someone may be sleeping.
+ This is simple enough to work on all architectures, but has the
+ problem that if we never "up" the semaphore it could eventually
+ wrap around. */
+
+/* FIXME: This may be way too small. --RR */
+#define FUTEX_HASHBITS 6
+
+/* We use this instead of a normal wait_queue_t, so we can wake only
+ the relevent ones (hashed queues may be shared) */
+struct futex_q {
+ struct list_head list;
+ struct task_struct *task;
+ /* Page struct and offset within it. */
+ struct page *page;
+ unsigned int offset;
+};
+
+/* The key for the hash is the address + index + offset within page */
+static struct list_head futex_queues[1<<FUTEX_HASHBITS];
+static spinlock_t futex_lock = SPIN_LOCK_UNLOCKED;
+
+static inline struct list_head *hash_futex(struct page *page,
+ unsigned long offset)
+{
+ unsigned long h;
+
+ /* struct page is shared, so we can hash on its address */
+ h = (unsigned long)page + offset;
+ return &futex_queues[hash_long(h, FUTEX_HASHBITS)];
+}
+
+static inline void wake_one_waiter(struct list_head *head,
+ struct page *page,
+ unsigned int offset)
+{
+ struct list_head *i;
+
+ spin_lock(&futex_lock);
+ list_for_each(i, head) {
+ struct futex_q *this = list_entry(i, struct futex_q, list);
+
+ if (this->page == page && this->offset == offset) {
+ wake_up_process(this->task);
+ break;
+ }
+ }
+ spin_unlock(&futex_lock);
+}
+
+/* Add at end to avoid starvation */
+static inline void queue_me(struct list_head *head,
+ struct futex_q *q,
+ struct page *page,
+ unsigned int offset)
+{
+ q->task = current;
+ q->page = page;
+ q->offset = offset;
+
+ spin_lock(&futex_lock);
+ list_add_tail(&q->list, head);
+ spin_unlock(&futex_lock);
+}
+
+static inline void unqueue_me(struct futex_q *q)
+{
+ spin_lock(&futex_lock);
+ list_del(&q->list);
+ spin_unlock(&futex_lock);
+}
+
+/* Get kernel address of the user page and pin it. */
+static struct page *pin_page(unsigned long page_start)
+{
+ struct mm_struct *mm = current->mm;
+ struct page *page;
+ int err;
+
+ down_read(&mm->mmap_sem);
+ err = get_user_pages(current, current->mm, page_start,
+ 1 /* one page */,
+ 1 /* writable */,
+ 0 /* don't force */,
+ &page,
+ NULL /* don't return vmas */);
+ up_read(&mm->mmap_sem);
+
+ if (err < 0)
+ return ERR_PTR(err);
+ return page;
+}
+
+/* Try to decrement the user count to zero. */
+static int decrement_to_zero(struct page *page, unsigned int offset)
+{
+ atomic_t *count;
+ int ret = 0;
+
+ count = kmap(page) + offset;
+ /* If we take the semaphore from 1 to 0, it's ours. If it's
+ zero, decrement anyway, to indicate we are waiting. If
+ it's negative, don't decrement so we don't wrap... */
+ if (atomic_read(count) >= 0 && atomic_dec_and_test(count))
+ ret = 1;
+ kunmap(page);
+ return ret;
+}
+
+/* Simplified from arch/ppc/kernel/semaphore.c: Paul M. is a genius. */
+static int futex_down(struct list_head *head, struct page *page, int offset)
+{
+ int retval = 0;
+ struct futex_q q;
+
+ current->state = TASK_INTERRUPTIBLE;
+ queue_me(head, &q, page, offset);
+
+ while (!decrement_to_zero(page, offset)) {
+ if (signal_pending(current)) {
+ retval = -EINTR;
+ break;
+ }
+ schedule();
+ current->state = TASK_INTERRUPTIBLE;
+ }
+ current->state = TASK_RUNNING;
+ unqueue_me(&q);
+ /* If we were signalled, we might have just been woken: we
+ must wake another one. Otherwise we need to wake someone
+ else (if they are waiting) so they drop the count below 0,
+ and when we "up" in userspace, we know there is a
+ waiter. */
+ wake_one_waiter(head, page, offset);
+ return retval;
+}
+
+static int futex_up(struct list_head *head, struct page *page, int offset)
+{
+ atomic_t *count;
+
+ count = kmap(page) + offset;
+ atomic_set(count, 1);
+ smp_wmb();
+ kunmap(page);
+ wake_one_waiter(head, page, offset);
+ return 0;
+}
+
+asmlinkage int sys_futex(void *uaddr, int op)
+{
+ int ret;
+ unsigned long pos_in_page;
+ struct list_head *head;
+ struct page *page;
+
+ pos_in_page = ((unsigned long)uaddr) % PAGE_SIZE;
+
+ /* Must be "naturally" aligned, and not on page boundary. */
+ if ((pos_in_page % __alignof__(atomic_t)) != 0
+ || pos_in_page + sizeof(atomic_t) > PAGE_SIZE)
+ return -EINVAL;
+
+ /* Simpler if it doesn't vanish underneath us. */
+ page = pin_page((unsigned long)uaddr - pos_in_page);
+ if (IS_ERR(page))
+ return PTR_ERR(page);
+
+ head = hash_futex(page, pos_in_page);
+ switch (op) {
+ case FUTEX_UP:
+ ret = futex_up(head, page, pos_in_page);
+ break;
+ case FUTEX_DOWN:
+ ret = futex_down(head, page, pos_in_page);
+ break;
+ /* Add other lock types here... */
+ default:
+ ret = -EINVAL;
+ }
+ put_page(page);
+
+ return ret;
+}
+
+static int __init init(void)
+{
+ unsigned int i;
+
+ for (i = 0; i < ARRAY_SIZE(futex_queues); i++)
+ INIT_LIST_HEAD(&futex_queues[i]);
+ return 0;
+}
+__initcall(init);
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