exit_lwps, lwp_wait: fix a race condition by re-trying if p_lock was dropped
in a case of process exit. Necessary to re-flag all LWPs for exit, as their state might have changed or new LWPs spawned. Should fix PR/46168 and PR/46402.
This commit is contained in:
rmind
parent
5c5a76d566
commit
ea775f7598
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@ -1,4 +1,4 @@
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/* $NetBSD: kern_exit.c,v 1.241 2012/08/05 14:53:25 riastradh Exp $ */
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/* $NetBSD: kern_exit.c,v 1.242 2012/09/27 20:43:15 rmind Exp $ */
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/*-
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* Copyright (c) 1998, 1999, 2006, 2007, 2008 The NetBSD Foundation, Inc.
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@ -67,7 +67,7 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: kern_exit.c,v 1.241 2012/08/05 14:53:25 riastradh Exp $");
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__KERNEL_RCSID(0, "$NetBSD: kern_exit.c,v 1.242 2012/09/27 20:43:15 rmind Exp $");
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#include "opt_ktrace.h"
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#include "opt_perfctrs.h"
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@ -599,17 +599,14 @@ exit1(struct lwp *l, int rv)
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void
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exit_lwps(struct lwp *l)
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{
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struct proc *p;
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struct lwp *l2;
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int error;
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lwpid_t waited;
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proc_t *p = l->l_proc;
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lwp_t *l2;
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int nlocks;
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KERNEL_UNLOCK_ALL(l, &nlocks);
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p = l->l_proc;
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KASSERT(mutex_owned(p->p_lock));
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retry:
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KASSERT(mutex_owned(p->p_lock));
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/*
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* Interrupt LWPs in interruptable sleep, unsuspend suspended
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* LWPs and then wait for everyone else to finish.
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@ -623,30 +620,20 @@ retry:
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l2->l_stat == LSSUSPENDED || l2->l_stat == LSSTOP) {
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/* setrunnable() will release the lock. */
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setrunnable(l2);
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DPRINTF(("exit_lwps: Made %d.%d runnable\n",
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p->p_pid, l2->l_lid));
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continue;
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}
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lwp_unlock(l2);
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}
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/*
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* Wait for every LWP to exit. Note: LWPs can get suspended/slept
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* behind us or there may even be new LWPs created. Therefore, a
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* full retry is required on error.
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*/
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while (p->p_nlwps > 1) {
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DPRINTF(("exit_lwps: waiting for %d LWPs (%d zombies)\n",
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p->p_nlwps, p->p_nzlwps));
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error = lwp_wait1(l, 0, &waited, LWPWAIT_EXITCONTROL);
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if (p->p_nlwps == 1)
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break;
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if (error == EDEADLK) {
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/*
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* LWPs can get suspended/slept behind us.
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* (eg. sa_setwoken)
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* kick them again and retry.
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*/
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if (lwp_wait(l, 0, NULL, true)) {
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goto retry;
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}
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if (error)
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panic("exit_lwps: lwp_wait1 failed with error %d",
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error);
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DPRINTF(("exit_lwps: Got LWP %d from lwp_wait1()\n", waited));
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}
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KERNEL_LOCK(nlocks, l);
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@ -1,4 +1,4 @@
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/* $NetBSD: kern_lwp.c,v 1.172 2012/08/30 02:26:02 matt Exp $ */
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/* $NetBSD: kern_lwp.c,v 1.173 2012/09/27 20:43:15 rmind Exp $ */
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/*-
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* Copyright (c) 2001, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
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@ -211,7 +211,7 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.172 2012/08/30 02:26:02 matt Exp $");
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__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.173 2012/09/27 20:43:15 rmind Exp $");
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#include "opt_ddb.h"
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#include "opt_lockdebug.h"
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@ -533,22 +533,21 @@ lwp_unstop(struct lwp *l)
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* Must be called with p->p_lock held.
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*/
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int
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lwp_wait1(struct lwp *l, lwpid_t lid, lwpid_t *departed, int flags)
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lwp_wait(struct lwp *l, lwpid_t lid, lwpid_t *departed, bool exiting)
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{
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struct proc *p = l->l_proc;
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struct lwp *l2;
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int nfound, error;
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lwpid_t curlid;
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bool exiting;
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const lwpid_t curlid = l->l_lid;
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proc_t *p = l->l_proc;
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lwp_t *l2;
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int error;
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KASSERT(mutex_owned(p->p_lock));
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p->p_nlwpwait++;
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l->l_waitingfor = lid;
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curlid = l->l_lid;
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exiting = ((flags & LWPWAIT_EXITCONTROL) != 0);
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for (;;) {
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int nfound;
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/*
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* Avoid a race between exit1() and sigexit(): if the
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* process is dumping core, then we need to bail out: call
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@ -558,10 +557,7 @@ lwp_wait1(struct lwp *l, lwpid_t lid, lwpid_t *departed, int flags)
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if ((p->p_sflag & PS_WCORE) != 0) {
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mutex_exit(p->p_lock);
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lwp_userret(l);
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#ifdef DIAGNOSTIC
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panic("lwp_wait1");
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#endif
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/* NOTREACHED */
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KASSERT(false);
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}
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/*
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@ -651,13 +647,14 @@ lwp_wait1(struct lwp *l, lwpid_t lid, lwpid_t *departed, int flags)
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}
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/*
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* The kernel is careful to ensure that it can not deadlock
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* when exiting - just keep waiting.
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* Note: since the lock will be dropped, need to restart on
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* wakeup to run all LWPs again, e.g. there may be new LWPs.
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*/
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if (exiting) {
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KASSERT(p->p_nlwps > 1);
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cv_wait(&p->p_lwpcv, p->p_lock);
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continue;
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error = EAGAIN;
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break;
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}
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/*
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@ -1,4 +1,4 @@
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/* $NetBSD: sys_lwp.c,v 1.54 2012/05/21 14:15:19 martin Exp $ */
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/* $NetBSD: sys_lwp.c,v 1.55 2012/09/27 20:43:15 rmind Exp $ */
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/*-
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* Copyright (c) 2001, 2006, 2007, 2008 The NetBSD Foundation, Inc.
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@ -35,7 +35,7 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: sys_lwp.c,v 1.54 2012/05/21 14:15:19 martin Exp $");
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__KERNEL_RCSID(0, "$NetBSD: sys_lwp.c,v 1.55 2012/09/27 20:43:15 rmind Exp $");
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#include <sys/param.h>
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#include <sys/systm.h>
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@ -354,19 +354,14 @@ sys__lwp_wait(struct lwp *l, const struct sys__lwp_wait_args *uap,
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lwpid_t dep;
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mutex_enter(p->p_lock);
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error = lwp_wait1(l, SCARG(uap, wait_for), &dep, 0);
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error = lwp_wait(l, SCARG(uap, wait_for), &dep, false);
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mutex_exit(p->p_lock);
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if (error)
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return error;
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if (SCARG(uap, departed)) {
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if (!error && SCARG(uap, departed)) {
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error = copyout(&dep, SCARG(uap, departed), sizeof(dep));
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if (error)
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return error;
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}
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return 0;
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return error;
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}
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int
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@ -1,4 +1,4 @@
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/* $NetBSD: lwp.h,v 1.163 2012/07/22 22:40:18 rmind Exp $ */
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/* $NetBSD: lwp.h,v 1.164 2012/09/27 20:43:15 rmind Exp $ */
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/*-
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* Copyright (c) 2001, 2006, 2007, 2008, 2009, 2010
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@ -315,9 +315,7 @@ void lwp_drainrefs(lwp_t *);
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bool lwp_alive(lwp_t *);
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lwp_t *lwp_find_first(proc_t *);
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/* Flags for _lwp_wait1 */
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#define LWPWAIT_EXITCONTROL 0x00000001
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int lwp_wait1(lwp_t *, lwpid_t, lwpid_t *, int);
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int lwp_wait(lwp_t *, lwpid_t, lwpid_t *, bool);
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void lwp_continue(lwp_t *);
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void lwp_unsleep(lwp_t *, bool);
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void lwp_unstop(lwp_t *);
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