/* * Copyright (c) 2002, Jeffrey Roberson * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice unmodified, this list of conditions, and the following * disclaimer. * 2. 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. * * 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. */ #include __FBSDID("$FreeBSD$"); #include #include #include #include #include #include #include #include #include #include #include #include #include struct umtx_q { LIST_ENTRY(umtx_q) uq_next; /* Linked list for the hash. */ TAILQ_HEAD(, thread) uq_tdq; /* List of threads blocked here. */ struct umtx *uq_umtx; /* Pointer key component. */ pid_t uq_pid; /* Pid key component. */ }; #define UMTX_QUEUES 128 #define UMTX_HASH(pid, umtx) \ (((uintptr_t)pid + ((uintptr_t)umtx & ~65535)) % UMTX_QUEUES) LIST_HEAD(umtx_head, umtx_q); static struct umtx_head queues[UMTX_QUEUES]; static MALLOC_DEFINE(M_UMTX, "umtx", "UMTX queue memory"); static struct mtx umtx_lock; MTX_SYSINIT(umtx, &umtx_lock, "umtx", MTX_DEF); #define UMTX_LOCK() mtx_lock(&umtx_lock); #define UMTX_UNLOCK() mtx_unlock(&umtx_lock); static struct umtx_q *umtx_lookup(struct thread *, struct umtx *umtx); static struct umtx_q *umtx_insert(struct thread *, struct umtx *umtx); static struct umtx_q * umtx_lookup(struct thread *td, struct umtx *umtx) { struct umtx_head *head; struct umtx_q *uq; pid_t pid; pid = td->td_proc->p_pid; head = &queues[UMTX_HASH(td->td_proc->p_pid, umtx)]; LIST_FOREACH(uq, head, uq_next) { if (uq->uq_pid == pid && uq->uq_umtx == umtx) return (uq); } return (NULL); } /* * Insert a thread onto the umtx queue. */ static struct umtx_q * umtx_insert(struct thread *td, struct umtx *umtx) { struct umtx_head *head; struct umtx_q *uq; pid_t pid; pid = td->td_proc->p_pid; if ((uq = umtx_lookup(td, umtx)) == NULL) { struct umtx_q *ins; UMTX_UNLOCK(); ins = malloc(sizeof(*uq), M_UMTX, M_ZERO | M_WAITOK); UMTX_LOCK(); /* * Some one else could have succeeded while we were blocked * waiting on memory. */ if ((uq = umtx_lookup(td, umtx)) == NULL) { head = &queues[UMTX_HASH(pid, umtx)]; uq = ins; uq->uq_pid = pid; uq->uq_umtx = umtx; LIST_INSERT_HEAD(head, uq, uq_next); TAILQ_INIT(&uq->uq_tdq); } else free(ins, M_UMTX); } /* * Insert us onto the end of the TAILQ. */ TAILQ_INSERT_TAIL(&uq->uq_tdq, td, td_umtx); return (uq); } static void umtx_remove(struct umtx_q *uq, struct thread *td) { TAILQ_REMOVE(&uq->uq_tdq, td, td_umtx); if (TAILQ_EMPTY(&uq->uq_tdq)) { LIST_REMOVE(uq, uq_next); free(uq, M_UMTX); } } int _umtx_lock(struct thread *td, struct _umtx_lock_args *uap) /* struct umtx *umtx */ { struct umtx_q *uq; struct umtx *umtx; intptr_t owner; intptr_t old; int error; uq = NULL; /* * Care must be exercised when dealing with this structure. It * can fault on any access. */ umtx = uap->umtx; for (;;) { /* * Try the uncontested case. This should be done in userland. */ owner = casuptr((intptr_t *)&umtx->u_owner, UMTX_UNOWNED, (intptr_t)td); /* The address was invalid. */ if (owner == -1) return (EFAULT); /* The acquire succeeded. */ if (owner == UMTX_UNOWNED) return (0); /* If no one owns it but it is contested try to acquire it. */ if (owner == UMTX_CONTESTED) { owner = casuptr((intptr_t *)&umtx->u_owner, UMTX_CONTESTED, ((intptr_t)td | UMTX_CONTESTED)); /* The address was invalid. */ if (owner == -1) return (EFAULT); if (owner == UMTX_CONTESTED) return (0); /* If this failed the lock has changed, restart. */ continue; } UMTX_LOCK(); uq = umtx_insert(td, umtx); UMTX_UNLOCK(); /* * Set the contested bit so that a release in user space * knows to use the system call for unlock. If this fails * either some one else has acquired the lock or it has been * released. */ old = casuptr((intptr_t *)&umtx->u_owner, owner, owner | UMTX_CONTESTED); /* The address was invalid. */ if (old == -1) { UMTX_LOCK(); umtx_remove(uq, td); UMTX_UNLOCK(); return (EFAULT); } /* * We set the contested bit, sleep. Otherwise the lock changed * and we need to retry or we lost a race to the thread * unlocking the umtx. */ UMTX_LOCK(); mtx_lock_spin(&sched_lock); if (old == owner && (td->td_flags & TDF_UMTXWAKEUP) == 0) { mtx_unlock_spin(&sched_lock); error = msleep(td, &umtx_lock, td->td_priority | PCATCH, "umtx", 0); mtx_lock_spin(&sched_lock); } else error = 0; td->td_flags &= ~TDF_UMTXWAKEUP; mtx_unlock_spin(&sched_lock); umtx_remove(uq, td); UMTX_UNLOCK(); /* * If we caught a signal we might have to retry or exit * immediately. */ if (error) return (error); } return (0); } int _umtx_unlock(struct thread *td, struct _umtx_unlock_args *uap) /* struct umtx *umtx */ { struct thread *blocked; struct umtx *umtx; struct umtx_q *uq; intptr_t owner; intptr_t old; umtx = uap->umtx; /* * Make sure we own this mtx. * * XXX Need a {fu,su}ptr this is not correct on arch where * sizeof(intptr_t) != sizeof(long). */ if ((owner = fuword(&umtx->u_owner)) == -1) return (EFAULT); if ((struct thread *)(owner & ~UMTX_CONTESTED) != td) return (EPERM); /* We should only ever be in here for contested locks */ KASSERT((owner & UMTX_CONTESTED) != 0, ("contested umtx is not.")); /* * When unlocking the umtx, it must be marked as unowned if * there is zero or one thread only waiting for it. * Otherwise, it must be marked as contested. */ UMTX_LOCK(); uq = umtx_lookup(td, umtx); if (uq == NULL || (uq != NULL && (blocked = TAILQ_FIRST(&uq->uq_tdq)) != NULL && TAILQ_NEXT(blocked, td_umtx) == NULL)) { UMTX_UNLOCK(); old = casuptr((intptr_t *)&umtx->u_owner, owner, UMTX_UNOWNED); if (old == -1) return (EFAULT); KASSERT(old != owner, ("improper umtx access")); /* * Recheck the umtx queue to make sure another thread * didn't put itself on it after it was unlocked. */ UMTX_LOCK(); uq = umtx_lookup(td, umtx); if (uq != NULL && ((blocked = TAILQ_FIRST(&uq->uq_tdq)) != NULL && TAILQ_NEXT(blocked, td_umtx) != NULL)) { UMTX_UNLOCK(); old = casuptr((intptr_t *)&umtx->u_owner, UMTX_UNOWNED, UMTX_CONTESTED); } else { UMTX_UNLOCK(); } } else { UMTX_UNLOCK(); old = casuptr((intptr_t *)&umtx->u_owner, owner, UMTX_CONTESTED); KASSERT(old != -1 && old != owner, ("improper umtx access")); } if (old == -1) return (EFAULT); /* * If there is a thread waiting on the umtx, wake it up. */ if (blocked != NULL) { mtx_lock_spin(&sched_lock); blocked->td_flags |= TDF_UMTXWAKEUP; mtx_unlock_spin(&sched_lock); wakeup(blocked); } return (0); }