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850108c0b4
instead of long types for low-level locks. Add prototypes for some internal libc functions that are wrapped by the library as cancellation points. Add memory barriers to alpha atomic swap functions (submitted by davidxu). Requested by: bde
301 lines
8.1 KiB
C
301 lines
8.1 KiB
C
/*-
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* Copyright (c) 2001, 2003 Daniel Eischen <deischen@freebsd.org>.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#include <sys/types.h>
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#include <machine/atomic.h>
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#include <assert.h>
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#include <stdlib.h>
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#include "atomic_ops.h"
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#include "lock.h"
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#define LCK_ASSERT assert
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#define MAX_SPINS 500
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void
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_lock_destroy(struct lock *lck)
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{
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if ((lck != NULL) && (lck->l_head != NULL)) {
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free(lck->l_head);
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lck->l_head = NULL;
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lck->l_tail = NULL;
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}
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}
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int
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_lock_init(struct lock *lck, enum lock_type ltype,
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lock_handler_t *waitfunc, lock_handler_t *wakeupfunc)
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{
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if (lck == NULL)
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return (-1);
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else if ((lck->l_head = malloc(sizeof(struct lockreq))) == NULL)
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return (-1);
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else {
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lck->l_type = ltype;
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lck->l_wait = waitfunc;
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lck->l_wakeup = wakeupfunc;
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lck->l_head->lr_locked = 0;
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lck->l_head->lr_watcher = NULL;
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lck->l_head->lr_owner = NULL;
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lck->l_head->lr_active = 1;
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lck->l_tail = lck->l_head;
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}
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return (0);
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}
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int
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_lockuser_init(struct lockuser *lu, void *priv)
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{
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if (lu == NULL)
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return (-1);
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else if ((lu->lu_myreq == NULL) &&
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((lu->lu_myreq = malloc(sizeof(struct lockreq))) == NULL))
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return (-1);
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else {
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lu->lu_myreq->lr_locked = 1;
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lu->lu_myreq->lr_watcher = NULL;
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lu->lu_myreq->lr_owner = lu;
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lu->lu_myreq->lr_active = 0;
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lu->lu_watchreq = NULL;
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lu->lu_priority = 0;
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lu->lu_private = priv;
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lu->lu_private2 = NULL;
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}
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return (0);
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}
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void
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_lockuser_destroy(struct lockuser *lu)
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{
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if ((lu != NULL) && (lu->lu_myreq != NULL))
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free(lu->lu_myreq);
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}
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/*
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* Acquire a lock waiting (spin or sleep) for it to become available.
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*/
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void
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_lock_acquire(struct lock *lck, struct lockuser *lu, int prio)
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{
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int i;
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int lval;
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/**
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* XXX - We probably want to remove these checks to optimize
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* performance. It is also a bug if any one of the
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* checks fail, so it's probably better to just let it
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* SEGV and fix it.
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*/
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#if 0
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if (lck == NULL || lu == NULL || lck->l_head == NULL)
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return;
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#endif
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if ((lck->l_type & LCK_PRIORITY) == 0)
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atomic_swap_ptr(&lck->l_head, lu->lu_myreq, &lu->lu_watchreq);
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else {
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LCK_ASSERT(lu->lu_myreq->lr_locked == 1);
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LCK_ASSERT(lu->lu_myreq->lr_watcher == NULL);
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LCK_ASSERT(lu->lu_myreq->lr_owner == lu);
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LCK_ASSERT(lu->lu_watchreq == NULL);
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lu->lu_priority = prio;
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/*
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* Atomically swap the head of the lock request with
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* this request.
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*/
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atomic_swap_ptr(&lck->l_head, lu->lu_myreq, &lu->lu_watchreq);
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}
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if (lu->lu_watchreq->lr_locked != 0) {
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atomic_store_rel_ptr(&lu->lu_watchreq->lr_watcher, lu);
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if ((lck->l_wait == NULL) ||
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((lck->l_type & LCK_ADAPTIVE) == 0)) {
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while (lu->lu_watchreq->lr_locked == 0)
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; /* spin, then yield? */
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} else {
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/*
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* Spin for a bit before invoking the wait function.
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*
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* We should be a little smarter here. If we're
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* running on a single processor, then the lock
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* owner got preempted and spinning will accomplish
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* nothing but waste time. If we're running on
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* multiple processors, the owner could be running
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* on another CPU and we might acquire the lock if
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* we spin for a bit.
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*
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* The other thing to keep in mind is that threads
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* acquiring these locks are considered to be in
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* critical regions; they will not be preempted by
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* the _UTS_ until they release the lock. It is
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* therefore safe to assume that if a lock can't
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* be acquired, it is currently held by a thread
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* running in another KSE.
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*/
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for (i = 0; i < MAX_SPINS; i++) {
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if (lu->lu_watchreq->lr_locked == 0)
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return;
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if (lu->lu_watchreq->lr_active == 0)
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break;
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}
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atomic_swap_int((int *)&lu->lu_watchreq->lr_locked,
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2, &lval);
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if (lval == 0)
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lu->lu_watchreq->lr_locked = 0;
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else
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lck->l_wait(lck, lu);
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}
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}
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lu->lu_myreq->lr_active = 1;
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}
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/*
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* Release a lock.
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*/
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void
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_lock_release(struct lock *lck, struct lockuser *lu)
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{
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struct lockuser *lu_tmp, *lu_h;
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struct lockreq *myreq;
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int prio_h;
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int lval;
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/**
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* XXX - We probably want to remove these checks to optimize
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* performance. It is also a bug if any one of the
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* checks fail, so it's probably better to just let it
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* SEGV and fix it.
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*/
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#if 0
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if ((lck == NULL) || (lu == NULL))
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return;
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#endif
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if ((lck->l_type & LCK_PRIORITY) != 0) {
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prio_h = 0;
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lu_h = NULL;
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/* Update tail if our request is last. */
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if (lu->lu_watchreq->lr_owner == NULL) {
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atomic_store_rel_ptr(&lck->l_tail, lu->lu_myreq);
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atomic_store_rel_ptr(&lu->lu_myreq->lr_owner, NULL);
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} else {
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/* Remove ourselves from the list. */
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atomic_store_rel_ptr(&lu->lu_myreq->lr_owner,
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lu->lu_watchreq->lr_owner);
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atomic_store_rel_ptr(
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&lu->lu_watchreq->lr_owner->lu_myreq, lu->lu_myreq);
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}
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/*
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* The watch request now becomes our own because we've
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* traded away our previous request. Save our previous
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* request so that we can grant the lock.
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*/
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myreq = lu->lu_myreq;
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lu->lu_myreq = lu->lu_watchreq;
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lu->lu_watchreq = NULL;
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lu->lu_myreq->lr_locked = 1;
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lu->lu_myreq->lr_owner = lu;
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lu->lu_myreq->lr_watcher = NULL;
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/*
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* Traverse the list of lock requests in reverse order
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* looking for the user with the highest priority.
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*/
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for (lu_tmp = lck->l_tail->lr_watcher; lu_tmp != NULL;
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lu_tmp = lu_tmp->lu_myreq->lr_watcher) {
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if (lu_tmp->lu_priority > prio_h) {
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lu_h = lu_tmp;
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prio_h = lu_tmp->lu_priority;
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}
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}
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if (lu_h != NULL) {
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/* Give the lock to the highest priority user. */
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if (lck->l_wakeup != NULL) {
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atomic_swap_int(
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(int *)&lu_h->lu_watchreq->lr_locked,
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0, &lval);
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if (lval == 2)
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/* Notify the sleeper */
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lck->l_wakeup(lck,
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lu_h->lu_myreq->lr_watcher);
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}
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else
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atomic_store_rel_int(
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&lu_h->lu_watchreq->lr_locked, 0);
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} else {
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if (lck->l_wakeup != NULL) {
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atomic_swap_int((int *)&myreq->lr_locked,
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0, &lval);
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if (lval == 2)
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/* Notify the sleeper */
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lck->l_wakeup(lck, myreq->lr_watcher);
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}
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else
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/* Give the lock to the previous request. */
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atomic_store_rel_int(&myreq->lr_locked, 0);
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}
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} else {
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/*
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* The watch request now becomes our own because we've
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* traded away our previous request. Save our previous
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* request so that we can grant the lock.
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*/
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myreq = lu->lu_myreq;
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lu->lu_myreq = lu->lu_watchreq;
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lu->lu_watchreq = NULL;
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lu->lu_myreq->lr_locked = 1;
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if (lck->l_wakeup) {
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atomic_swap_int((int *)&myreq->lr_locked, 0, &lval);
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if (lval == 2)
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/* Notify the sleeper */
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lck->l_wakeup(lck, myreq->lr_watcher);
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}
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else
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/* Give the lock to the previous request. */
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atomic_store_rel_int(&myreq->lr_locked, 0);
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}
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lu->lu_myreq->lr_active = 0;
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}
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void
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_lock_grant(struct lock *lck /* unused */, struct lockuser *lu)
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{
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atomic_store_rel_int(&lu->lu_watchreq->lr_locked, 3);
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}
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void
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_lockuser_setactive(struct lockuser *lu, int active)
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{
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lu->lu_myreq->lr_active = active;
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}
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