freebsd-dev/sys/kern/kern_umtx.c
Jake Burkholder cef57e7624 - Make casuptr return the old value of the location we're trying to update,
and change the umtx code to expect this.

Reviewed by:	jeff
2003-04-02 08:02:27 +00:00

307 lines
6.8 KiB
C

/*
* Copyright (c) 2002, Jeffrey Roberson <jeff@freebsd.org>
* 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.
*
* $FreeBSD$
*
*/
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/signalvar.h>
#include <sys/sysent.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/thr.h>
#include <sys/umtx.h>
int
_umtx_lock(struct thread *td, struct _umtx_lock_args *uap)
/* struct umtx *umtx */
{
struct umtx *umtx;
struct thread *blocked;
intptr_t owner;
intptr_t old;
int error;
error = 0;
/*
* Care must be exercised when dealing with this structure. It
* can fault on any access.
*/
umtx = uap->umtx;
PROC_LOCK(td->td_proc);
for (;;) {
/*
* Try the uncontested case. This should be done in userland.
*/
owner = casuptr((intptr_t *)&umtx->u_owner,
UMTX_UNOWNED, (intptr_t)td);
/* The acquire succeeded. */
if (owner == UMTX_UNOWNED) {
error = 0;
goto out;
}
/* The address was invalid. */
if (owner == -1) {
error = EFAULT;
goto out;
}
if (owner & UMTX_CONTESTED)
break;
/*
* 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);
/* We set the contested bit. */
if (old == owner)
break;
/* The address was invalid. */
if (old == -1) {
error = EFAULT;
goto out;
}
/* We didn't set the contested bit, try again. */
}
/*
* We are now protected from further races via the proc lock.
* If userland messes with their mutex without using cmpset
* they will deadlock themselves but they will still be
* killable via signals.
*/
if ((owner = fuword(&umtx->u_blocked)) == -1) {
error = EFAULT;
goto out;
}
if (owner == UMTX_UNOWNED) {
if (suword(&umtx->u_blocked, (long)td) == -1) {
error = EFAULT;
goto out;
}
/*
* Other blocked threads will reside here.
*/
STAILQ_INIT(&td->td_umtxq);
} else {
FOREACH_THREAD_IN_PROC(td->td_proc, blocked)
if (blocked == (struct thread *)(owner))
break;
if (blocked == NULL) {
error = EINVAL;
goto out;
}
/*
* Insert us onto the end of the TAILQ.
*/
STAILQ_INSERT_TAIL(&blocked->td_umtxq, td, td_umtx);
}
for (;;) {
/*
* Sleep until we can acquire the lock. We must still deliver
* signals so that they are not deferred until we acquire the
* lock which may be never. The threads actual priority is
* used to maintain proper ordering.
*/
error = msleep(&td->td_umtx, &td->td_proc->p_mtx,
td->td_priority | PCATCH, "umtx", 0);
/*
* When we are woken up we need to see if we now own the lock
* even if a signal was delivered.
*/
if ((owner = fuword(&umtx->u_owner)) == -1) {
error = EFAULT;
break;
}
owner &= ~UMTX_CONTESTED;
if ((struct thread *)owner == td) {
error = 0;
break;
}
/*
* We may have signals to deliver.
*/
if (error)
break;
}
out:
PROC_UNLOCK(td->td_proc);
return (error);
}
int
_umtx_unlock(struct thread *td, struct _umtx_unlock_args *uap)
/* struct umtx *umtx */
{
struct thread *td0;
struct umtx *umtx;
intptr_t owner;
intptr_t blocked;
intptr_t old;
int error;
error = 0;
umtx = uap->umtx;
PROC_LOCK(td->td_proc);
/*
* 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) {
error = EFAULT;
goto out;
}
if ((struct thread *)(owner & ~UMTX_CONTESTED) != td) {
error = EPERM;
goto out;
}
/*
* If we own it but it isn't contested then we can just release and
* return.
*/
if ((owner & UMTX_CONTESTED) == 0) {
owner = casuptr((intptr_t *)&umtx->u_owner,
(intptr_t)td, UMTX_UNOWNED);
if (owner == -1)
error = EFAULT;
/*
* If this failed someone modified the memory without going
* through this api.
*/
else if (owner != (intptr_t)td)
error = EINVAL;
else
error = 0;
goto out;
}
/*
* Since we own the mutex and the proc lock we are free to inspect
* the blocked queue. It must have one valid entry since the
* CONTESTED bit was set.
*/
blocked = fuword(&umtx->u_blocked);
if (blocked == -1) {
error = EFAULT;
goto out;
}
if (blocked == 0) {
error = EINVAL;
goto out;
}
FOREACH_THREAD_IN_PROC(td->td_proc, td0)
if (td0 == (struct thread *)blocked)
break;
if (td0 == NULL) {
error = EINVAL;
goto out;
}
if (!STAILQ_EMPTY(&td0->td_umtxq)) {
struct thread *next;
blocked |= UMTX_CONTESTED;
next = STAILQ_FIRST(&td0->td_umtxq);
if (suword(&umtx->u_blocked, (long)next) == -1) {
error = EFAULT;
goto out;
}
STAILQ_REMOVE_HEAD(&td0->td_umtxq, td_umtx);
/*
* Switch the queue over to the next blocked thread.
*/
if (!STAILQ_EMPTY(&td0->td_umtxq)) {
next->td_umtxq = td0->td_umtxq;
STAILQ_INIT(&td0->td_umtxq);
} else
STAILQ_INIT(&next->td_umtxq);
} else {
if (suword(&umtx->u_blocked, UMTX_UNOWNED) == -1) {
error = EFAULT;
goto out;
}
}
/*
* Now directly assign this mutex to the first thread that was
* blocked on it.
*/
old = casuptr((intptr_t *)&umtx->u_owner, owner, blocked);
/*
* This will only happen if someone modifies the lock without going
* through this api.
*/
if (old != owner) {
error = EINVAL;
goto out;
}
if (old == -1) {
error = EFAULT;
goto out;
}
/* Success. */
error = 0;
wakeup(&td0->td_umtx);
out:
PROC_UNLOCK(td->td_proc);
return (error);
}