- Add an api for doing smp safe locks in userland.
- umtx_lock() is defined as an inline in umtx.h. It tries to do an uncontested acquire of a lock which falls back to the _umtx_lock() system-call if that fails. - umtx_unlock() is also an inline which falls back to _umtx_unlock() if the uncontested unlock fails. - Locks are keyed off of the thr_id_t of the currently running thread which is currently just the pointer to the 'struct thread' in kernel. - _umtx_lock() uses the proc pointer to synchronize access to blocked thread queues which are stored in the first blocked thread.
This commit is contained in:
Jeff Roberson
parent
90e38817b7
commit
69404b5090
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=112904
303
sys/kern/kern_umtx.c
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303
sys/kern/kern_umtx.c
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@ -0,0 +1,303 @@
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/*
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* Copyright (c) 2002, Jeffrey Roberson <jeff@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 unmodified, this list of conditions, and the following
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* 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 AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* $FreeBSD$
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*
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*/
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/proc.h>
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#include <sys/signalvar.h>
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#include <sys/sysent.h>
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#include <sys/systm.h>
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#include <sys/sysproto.h>
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#include <sys/thr.h>
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#include <sys/umtx.h>
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int
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_umtx_lock(struct thread *td, struct _umtx_lock_args *uap)
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/* struct umtx *umtx */
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{
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struct umtx *umtx;
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struct thread *blocked;
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intptr_t owner;
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int error;
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error = 0;
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/*
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* Care must be exercised when dealing with this structure. It
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* can fault on any access.
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*/
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umtx = uap->umtx;
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PROC_LOCK(td->td_proc);
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for (;;) {
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/*
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* Try the uncontested case. This should be done in userland.
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*/
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owner = casuptr((intptr_t *)&umtx->u_owner,
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UMTX_UNOWNED, (intptr_t)td);
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/* The acquire succeeded. */
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if (owner == (intptr_t)td) {
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error = 0;
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goto out;
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}
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/* The address was invalid. */
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if (owner == -1) {
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error = EFAULT;
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goto out;
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}
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if (owner & UMTX_CONTESTED)
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break;
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/*
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* Set the contested bit so that a release in user space
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* knows to use the system call for unlock. If this fails
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* either some one else has acquired the lock or it has been
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* released.
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*/
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owner = casuptr((intptr_t *)&umtx->u_owner, owner, owner | UMTX_CONTESTED);
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/* The contested bit was set. */
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if (owner & UMTX_CONTESTED)
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break;
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/* The address was invalid. */
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if (owner == -1) {
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error = EFAULT;
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goto out;
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}
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/* We didn't set the contested bit, try again. */
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}
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/*
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* We are now protected from further races via the proc lock.
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* If userland messes with their mutex without using cmpset
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* they will deadlock themselves but they will still be
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* killable via signals.
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*/
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if ((owner = fuword(&umtx->u_blocked)) == -1) {
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error = EFAULT;
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goto out;
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}
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if (owner == UMTX_UNOWNED) {
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if (suword(&umtx->u_blocked, (long)td) == -1) {
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error = EFAULT;
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goto out;
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}
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/*
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* Other blocked threads will reside here.
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*/
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STAILQ_INIT(&td->td_umtxq);
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} else {
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FOREACH_THREAD_IN_PROC(td->td_proc, blocked)
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if (blocked == (struct thread *)(owner))
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break;
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if (blocked == NULL) {
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error = EINVAL;
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goto out;
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}
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/*
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* Insert us onto the end of the TAILQ.
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*/
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STAILQ_INSERT_TAIL(&blocked->td_umtxq, td, td_umtx);
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}
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for (;;) {
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/*
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* Sleep until we can acquire the lock. We must still deliver
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* signals so that they are not deferred until we acquire the
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* lock which may be never. The threads actual priority is
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* used to maintain proper ordering.
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*/
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error = msleep(&td->td_umtx, &td->td_proc->p_mtx,
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td->td_priority | PCATCH, "umtx", 0);
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/*
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* When we are woken up we need to see if we now own the lock
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* even if a signal was delivered.
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*/
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if ((owner = fuword(&umtx->u_owner)) == -1) {
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error = EFAULT;
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break;
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}
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owner &= ~UMTX_CONTESTED;
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if ((struct thread *)owner == td) {
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error = 0;
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break;
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}
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/*
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* We may have signals to deliver.
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*/
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if (error)
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break;
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}
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out:
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PROC_UNLOCK(td->td_proc);
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return (error);
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}
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int
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_umtx_unlock(struct thread *td, struct _umtx_unlock_args *uap)
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/* struct umtx *umtx */
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{
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struct thread *td0;
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struct umtx *umtx;
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intptr_t owner;
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intptr_t blocked;
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int error;
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error = 0;
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umtx = uap->umtx;
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PROC_LOCK(td->td_proc);
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/*
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* Make sure we own this mtx.
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*
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* XXX Need a {fu,su}ptr this is not correct on arch where
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* sizeof(intptr_t) != sizeof(long).
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*/
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if ((owner = fuword(&umtx->u_owner)) == -1) {
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error = EFAULT;
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goto out;
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}
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if ((struct thread *)(owner & ~UMTX_CONTESTED) != td) {
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error = EPERM;
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goto out;
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}
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/*
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* If we own it but it isn't contested then we can just release and
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* return.
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*/
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if ((owner & UMTX_CONTESTED) == 0) {
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owner = casuptr((intptr_t *)&umtx->u_owner,
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(intptr_t)td, UMTX_UNOWNED);
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if (owner == -1)
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error = EFAULT;
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/*
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* If this failed someone modified the memory without going
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* through this api.
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*/
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else if (owner != UMTX_UNOWNED)
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error = EINVAL;
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else
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error = 0;
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goto out;
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}
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/*
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* Since we own the mutex and the proc lock we are free to inspect
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* the blocked queue. It must have one valid entry since the
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* CONTESTED bit was set.
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*/
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blocked = fuword(&umtx->u_blocked);
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if (blocked == -1){
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error = EFAULT;
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goto out;
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}
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if (blocked == 0) {
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error = EINVAL;
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goto out;
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}
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FOREACH_THREAD_IN_PROC(td->td_proc, td0)
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if (td0 == (struct thread *)blocked)
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break;
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if (td0 == NULL) {
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error = EINVAL;
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goto out;
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}
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if (!STAILQ_EMPTY(&td0->td_umtxq)) {
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struct thread *next;
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blocked |= UMTX_CONTESTED;
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next = STAILQ_FIRST(&td0->td_umtxq);
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if (suword(&umtx->u_blocked, (long)next) == -1) {
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error = EFAULT;
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goto out;
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}
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STAILQ_REMOVE_HEAD(&td0->td_umtxq, td_umtx);
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/*
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* Switch the queue over to the next blocked thread.
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*/
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if (!STAILQ_EMPTY(&td0->td_umtxq)) {
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next->td_umtxq = td0->td_umtxq;
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STAILQ_INIT(&td0->td_umtxq);
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} else
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STAILQ_INIT(&next->td_umtxq);
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} else {
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if (suword(&umtx->u_blocked, UMTX_UNOWNED) == -1) {
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error = EFAULT;
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goto out;
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}
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}
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/*
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* Now directly assign this mutex to the first thread that was
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* blocked on it.
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*/
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owner = casuptr((intptr_t *)&umtx->u_owner, owner, blocked);
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/*
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* This will only happen if someone modifies the lock without going
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* through this api.
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*/
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if (owner != blocked) {
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error = EINVAL;
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goto out;
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}
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if (owner == -1) {
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error = EFAULT;
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goto out;
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}
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/* Success. */
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error = 0;
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wakeup(&td0->td_umtx);
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out:
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PROC_UNLOCK(td->td_proc);
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return (error);
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}
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87
sys/sys/umtx.h
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87
sys/sys/umtx.h
Normal file
@ -0,0 +1,87 @@
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/*
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* Copyright (c) 2002, Jeffrey Roberson <jeff@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 unmodified, this list of conditions, and the following
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* 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 AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* $FreeBSD$
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*
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*/
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#ifndef _SYS_UMTX_H_
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#define _SYS_UMTX_H_
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/*
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* See pthread_*
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*/
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#define UMTX_UNOWNED NULL
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#define UMTX_CONTESTED 0x1
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struct umtx {
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thr_id_t u_owner; /* Owner of the mutex. */
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thr_id_t u_blocked; /* First blocked thread, owns wait queue. */
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};
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#ifndef _KERNEL
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/*
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* System calls for acquiring and releasing contested mutexes.
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*/
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int _umtx_lock(struct umtx *mtx);
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int _umtx_unlock(struct umtx *mtx);
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/*
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* Standard api. Try uncontested acquire/release and asks the
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* kernel to resolve failures.
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*/
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static __inline int
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umtx_lock(struct umtx *umtx, thr_id_t id)
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{
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if (atomic_cmpset_acq_ptr(&umtx->u_owner, UMTX_UNOWNED, id) == 0)
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if (_umtx_lock(umtx) == -1)
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return (errno);
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return (0);
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}
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static __inline int
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umtx_trylock(struct umtx *umtx, thr_id_t id)
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{
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if (atomic_cmpset_acq_ptr(&umtx->u_owner, UMTX_UNOWNED, id) == 0)
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return (EBUSY);
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return (0);
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}
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static __inline int
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umtx_unlock(struct umtx *umtx, thr_id_t id)
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{
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if (atomic_cmpset_rel_ptr(&umtx->u_owner, id, UMTX_UNOWNED) == 0)
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if (_umtx_unlock(umtx) == -1)
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return (errno);
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return (0);
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}
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#endif /* !_KERNEL */
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#endif /* !_SYS_UMTX_H_ */
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