Implement condition variables.

1 files changed, 547 insertions, 0 deletions

diff --git a/sys/kern/kern_condvar.c b/sys/kern/kern_condvar.c
new file mode 100644
index 0000000..2adee73
--- /dev/null
+++ b/sys/kern/kern_condvar.c
@@ -0,0 +1,547 @@
+/*-
+ * Copyright (c) 2000 Jake Burkholder <jake@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, 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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 "opt_ktrace.h"
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/proc.h>
+#include <sys/kernel.h>
+#include <sys/ktr.h>
+#include <sys/condvar.h>
+#include <sys/mutex.h>
+#include <sys/signalvar.h>
+#include <sys/resourcevar.h>
+#ifdef KTRACE
+#include <sys/uio.h>
+#include <sys/ktrace.h>
+#endif
+
+/*
+ * Common sanity checks for cv_wait* functions.
+ */
+#define	CV_ASSERT(cvp, mp, p) do {					\
+	KASSERT((p) != NULL, ("%s: curproc NULL", __FUNCTION__));	\
+	KASSERT((p)->p_stat == SRUN, ("%s: not SRUN", __FUNCTION__));	\
+	KASSERT((cvp) != NULL, ("%s: cvp NULL", __FUNCTION__));		\
+	KASSERT((mp) != NULL, ("%s: mp NULL", __FUNCTION__));		\
+	mtx_assert((mp), MA_OWNED | MA_NOTRECURSED);			\
+} while (0)
+
+#ifdef CV_DEBUG
+#define	CV_WAIT_VALIDATE(cvp, mp) do {					\
+	if (TAILQ_EMPTY(&(cvp)->cv_waitq)) {				\
+		/* Only waiter. */					\
+		(cvp)->cv_mtx = (mp);					\
+	} else {							\
+		/*							\
+		 * Other waiter; assert that we're using the		\
+		 * same mutex.						\
+		 */							\
+		KASSERT((cvp)->cv_mtx == (mp),				\
+		    ("%s: Multiple mutexes", __FUNCTION__));		\
+	}								\
+} while (0)
+#define	CV_SIGNAL_VALIDATE(cvp) do {					\
+	if (!TAILQ_EMPTY(&(cvp)->cv_waitq)) {				\
+		KASSERT(mtx_owned((cvp)->cv_mtx),			\
+		    ("%s: Mutex not owned", __FUNCTION__));		\
+	}								\
+} while (0)
+#else
+#define	CV_WAIT_VALIDATE(cvp, mp)
+#define	CV_SIGNAL_VALIDATE(cvp)
+#endif
+
+static void cv_timedwait_end(void *arg);
+
+/*
+ * Initialize a condition variable.  Must be called before use.
+ */
+void
+cv_init(struct cv *cvp, const char *desc)
+{
+
+	TAILQ_INIT(&cvp->cv_waitq);
+	cvp->cv_mtx = NULL;
+	cvp->cv_description = desc;
+}
+
+/*
+ * Destroy a condition variable.  The condition variable must be re-initialized
+ * in order to be re-used.
+ */
+void
+cv_destroy(struct cv *cvp)
+{
+
+	KASSERT(cv_waitq_empty(cvp), ("%s: cv_waitq non-empty", __FUNCTION__));
+}
+
+/*
+ * Common code for cv_wait* functions.  All require sched_lock.
+ */
+
+/*
+ * Switch context.
+ */
+static __inline void
+cv_switch(struct proc *p)
+{
+
+	p->p_stat = SSLEEP;
+	p->p_stats->p_ru.ru_nvcsw++;
+	mi_switch();
+	CTR3(KTR_PROC, "cv_switch: resume proc %p (pid %d, %s)", p, p->p_pid,
+	    p->p_comm);
+}
+
+/*
+ * Switch context, catching signals.
+ */
+static __inline int
+cv_switch_catch(struct proc *p)
+{
+	int sig;
+
+	/*
+	 * We put ourselves on the sleep queue and start our timeout before
+	 * calling CURSIG, as we could stop there, and a wakeup or a SIGCONT (or
+	 * both) could occur while we were stopped.  A SIGCONT would cause us to
+	 * be marked as SSLEEP without resuming us, thus we must be ready for
+	 * sleep when CURSIG is called.  If the wakeup happens while we're
+	 * stopped, p->p_wchan will be 0 upon return from CURSIG.
+	 */
+	p->p_flag |= P_SINTR;
+	mtx_exit(&sched_lock, MTX_SPIN);
+	/* proc_lock(p); */
+	sig = CURSIG(p);
+	mtx_enter(&sched_lock, MTX_SPIN);
+	/* proc_unlock_noswitch(p); */
+	if (sig != 0) {
+		if (p->p_wchan != NULL)
+			cv_waitq_remove(p);
+		p->p_stat = SRUN;
+	} else if (p->p_wchan != NULL) {
+		cv_switch(p);
+	}
+	p->p_flag &= ~P_SINTR;
+
+	return sig;
+}
+
+/*
+ * Add a process to the wait queue of a condition variable.
+ */
+static __inline void
+cv_waitq_add(struct cv *cvp, struct proc *p)
+{
+
+	/*
+	 * Process may be sitting on a slpque if asleep() was called, remove it
+	 * before re-adding.
+	 */
+	if (p->p_wchan != NULL)
+		unsleep(p);
+
+	p->p_flag |= P_CVWAITQ;
+	p->p_wchan = cvp;
+	p->p_wmesg = cvp->cv_description;
+	p->p_slptime = 0;
+	p->p_nativepri = p->p_priority;
+	CTR3(KTR_PROC, "cv_waitq_add: proc %p (pid %d, %s)", p, p->p_pid,
+	    p->p_comm);
+	TAILQ_INSERT_TAIL(&cvp->cv_waitq, p, p_slpq);
+}
+
+/*
+ * Wait on a condition variable.  The current process is placed on the condition
+ * variable's wait queue and suspended.  A cv_signal or cv_broadcast on the same
+ * condition variable will resume the process.  The mutex is released before
+ * sleeping and will be held on return.  It is recommended that the mutex be
+ * held when cv_signal or cv_broadcast are called.
+ */
+void
+cv_wait(struct cv *cvp, struct mtx *mp)
+{
+	struct proc *p;
+	WITNESS_SAVE_DECL(mp);
+
+	p = CURPROC;
+#ifdef KTRACE
+	if (p && KTRPOINT(p, KTR_CSW))
+		ktrcsw(p->p_tracep, 1, 0);
+#endif
+	CV_ASSERT(cvp, mp, p);
+	WITNESS_SLEEP(0, mp);
+	WITNESS_SAVE(mp, mp);
+
+	mtx_enter(&sched_lock, MTX_SPIN);
+	if (cold || panicstr) {
+		/*
+		 * After a panic, or during autoconfiguration, just give
+		 * interrupts a chance, then just return; don't run any other
+		 * procs or panic below, in case this is the idle process and
+		 * already asleep.
+		 */
+		mtx_exit(&sched_lock, MTX_SPIN);
+		return;
+	}
+	CV_WAIT_VALIDATE(cvp, mp);
+
+	DROP_GIANT_NOSWITCH();
+	mtx_exit(mp, MTX_DEF | MTX_NOSWITCH);
+
+	cv_waitq_add(cvp, p);
+	cv_switch(p);
+	curpriority = p->p_usrpri;
+
+	mtx_exit(&sched_lock, MTX_SPIN);
+#ifdef KTRACE
+	if (KTRPOINT(p, KTR_CSW))
+		ktrcsw(p->p_tracep, 0, 0);
+#endif
+	PICKUP_GIANT();
+	mtx_enter(mp, MTX_DEF);
+	WITNESS_RESTORE(mp, mp);
+}
+
+/*
+ * Wait on a condition variable, allowing interruption by signals.  Return 0 if
+ * the process was resumed with cv_signal or cv_broadcast, EINTR or ERESTART if
+ * a signal was caught.  If ERESTART is returned the system call should be
+ * restarted if possible.
+ */
+int
+cv_wait_sig(struct cv *cvp, struct mtx *mp)
+{
+	struct proc *p;
+	int rval;
+	int sig;
+	WITNESS_SAVE_DECL(mp);
+
+	p = CURPROC;
+	rval = 0;
+#ifdef KTRACE
+	if (p && KTRPOINT(p, KTR_CSW))
+		ktrcsw(p->p_tracep, 1, 0);
+#endif
+	CV_ASSERT(cvp, mp, p);
+	WITNESS_SLEEP(0, mp);
+	WITNESS_SAVE(mp, mp);
+
+	mtx_enter(&sched_lock, MTX_SPIN);
+	if (cold || panicstr) {
+		/*
+		 * After a panic, or during autoconfiguration, just give
+		 * interrupts a chance, then just return; don't run any other
+		 * procs or panic below, in case this is the idle process and
+		 * already asleep.
+		 */
+		mtx_exit(&sched_lock, MTX_SPIN);
+		return 0;
+	}
+	CV_WAIT_VALIDATE(cvp, mp);
+
+	DROP_GIANT_NOSWITCH();
+	mtx_exit(mp, MTX_DEF | MTX_NOSWITCH);
+
+	cv_waitq_add(cvp, p);
+	sig = cv_switch_catch(p);
+	curpriority = p->p_usrpri;
+
+	mtx_exit(&sched_lock, MTX_SPIN);
+	PICKUP_GIANT();
+
+	/* proc_lock(p); */
+	if (sig == 0)
+		sig = CURSIG(p);
+	if (sig != 0) {
+		if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
+			rval = EINTR;
+		else
+			rval = ERESTART;
+	}
+	/* proc_unlock(p); */
+
+#ifdef KTRACE
+	if (KTRPOINT(p, KTR_CSW))
+		ktrcsw(p->p_tracep, 0, 0);
+#endif
+	mtx_enter(mp, MTX_DEF);
+	WITNESS_RESTORE(mp, mp);
+
+	return (rval);
+}
+
+/*
+ * Wait on a condition variable for at most timo/hz seconds.  Returns 0 if the
+ * process was resumed by cv_signal or cv_broadcast, EWOULDBLOCK if the timeout
+ * expires.
+ */
+int
+cv_timedwait(struct cv *cvp, struct mtx *mp, int timo)
+{
+	struct proc *p;
+	int rval;
+	WITNESS_SAVE_DECL(mp);
+
+	p = CURPROC;
+	rval = 0;
+#ifdef KTRACE
+	if (p && KTRPOINT(p, KTR_CSW))
+		ktrcsw(p->p_tracep, 1, 0);
+#endif
+	CV_ASSERT(cvp, mp, p);
+	WITNESS_SLEEP(0, mp);
+	WITNESS_SAVE(mp, mp);
+
+	mtx_enter(&sched_lock, MTX_SPIN);
+	if (cold || panicstr) {
+		/*
+		 * After a panic, or during autoconfiguration, just give
+		 * interrupts a chance, then just return; don't run any other
+		 * procs or panic below, in case this is the idle process and
+		 * already asleep.
+		 */
+		mtx_exit(&sched_lock, MTX_SPIN);
+		return 0;
+	}
+	CV_WAIT_VALIDATE(cvp, mp);
+
+	DROP_GIANT_NOSWITCH();
+	mtx_exit(mp, MTX_DEF | MTX_NOSWITCH);
+
+	cv_waitq_add(cvp, p);
+	callout_reset(&p->p_slpcallout, timo, cv_timedwait_end, p);
+	cv_switch(p);
+	curpriority = p->p_usrpri;
+
+	if (p->p_flag & P_TIMEOUT) {
+		p->p_flag &= ~P_TIMEOUT;
+		rval = EWOULDBLOCK;
+	} else
+		callout_stop(&p->p_slpcallout);
+
+	mtx_exit(&sched_lock, MTX_SPIN);
+#ifdef KTRACE
+	if (KTRPOINT(p, KTR_CSW))
+		ktrcsw(p->p_tracep, 0, 0);
+#endif
+	PICKUP_GIANT();
+	mtx_enter(mp, MTX_DEF);
+	WITNESS_RESTORE(mp, mp);
+
+	return (rval);
+}
+
+/*
+ * Wait on a condition variable for at most timo/hz seconds, allowing
+ * interruption by signals.  Returns 0 if the process was resumed by cv_signal
+ * or cv_broadcast, EWOULDBLOCK if the timeout expires, and EINTR or ERESTART if
+ * a signal was caught.
+ */
+int
+cv_timedwait_sig(struct cv *cvp, struct mtx *mp, int timo)
+{
+	struct proc *p;
+	int rval;
+	int sig;
+	WITNESS_SAVE_DECL(mp);
+
+	p = CURPROC;
+	rval = 0;
+#ifdef KTRACE
+	if (p && KTRPOINT(p, KTR_CSW))
+		ktrcsw(p->p_tracep, 1, 0);
+#endif
+	CV_ASSERT(cvp, mp, p);
+	WITNESS_SLEEP(0, mp);
+	WITNESS_SAVE(mp, mp);
+
+	mtx_enter(&sched_lock, MTX_SPIN);
+	if (cold || panicstr) {
+		/*
+		 * After a panic, or during autoconfiguration, just give
+		 * interrupts a chance, then just return; don't run any other
+		 * procs or panic below, in case this is the idle process and
+		 * already asleep.
+		 */
+		mtx_exit(&sched_lock, MTX_SPIN);
+		return 0;
+	}
+	CV_WAIT_VALIDATE(cvp, mp);
+
+	DROP_GIANT_NOSWITCH();
+	mtx_exit(mp, MTX_DEF | MTX_NOSWITCH);
+
+	cv_waitq_add(cvp, p);
+	callout_reset(&p->p_slpcallout, timo, cv_timedwait_end, p);
+	sig = cv_switch_catch(p);
+	curpriority = p->p_usrpri;
+
+	if (p->p_flag & P_TIMEOUT) {
+		p->p_flag &= ~P_TIMEOUT;
+		rval = EWOULDBLOCK;
+	} else
+		callout_stop(&p->p_slpcallout);
+
+	mtx_exit(&sched_lock, MTX_SPIN);
+	PICKUP_GIANT();
+
+	/* proc_lock(p); */
+	if (sig == 0)
+		sig = CURSIG(p);
+	if (sig != 0) {
+		if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
+			rval = EINTR;
+		else
+			rval = ERESTART;
+	}
+	/* proc_unlock(p); */
+
+#ifdef KTRACE
+	if (KTRPOINT(p, KTR_CSW))
+		ktrcsw(p->p_tracep, 0, 0);
+#endif
+	mtx_enter(mp, MTX_DEF);
+	WITNESS_RESTORE(mp, mp);
+
+	return (rval);
+}
+
+/*
+ * Common code for signal and broadcast.  Assumes waitq is not empty.  Must be
+ * called with sched_lock held.
+ */
+static __inline void
+cv_wakeup(struct cv *cvp)
+{
+	struct proc *p;
+
+	p = TAILQ_FIRST(&cvp->cv_waitq);
+	KASSERT(p->p_wchan == cvp, ("%s: bogus wchan", __FUNCTION__));
+	KASSERT(p->p_flag & P_CVWAITQ, ("%s: not on waitq", __FUNCTION__));
+	TAILQ_REMOVE(&cvp->cv_waitq, p, p_slpq);
+	p->p_flag &= ~P_CVWAITQ;
+	p->p_wchan = 0;
+	if (p->p_stat == SSLEEP) {
+		/* OPTIMIZED EXPANSION OF setrunnable(p); */
+		CTR3(KTR_PROC, "cv_signal: proc %p (pid %d, %s)",
+		    p, p->p_pid, p->p_comm);
+		if (p->p_slptime > 1)
+			updatepri(p);
+		p->p_slptime = 0;
+		p->p_stat = SRUN;
+		if (p->p_flag & P_INMEM) {
+			setrunqueue(p);
+			maybe_resched(p);
+		} else {
+			p->p_flag |= P_SWAPINREQ;
+			wakeup(&proc0);
+		}
+		/* END INLINE EXPANSION */
+	}
+}
+
+/*
+ * Signal a condition variable, wakes up one waiting process.  Will also wakeup
+ * the swapper if the process is not in memory, so that it can bring the
+ * sleeping process in.  Note that this may also result in additional processes
+ * being made runnable.  Should be called with the same mutex as was passed to
+ * cv_wait held.
+ */
+void
+cv_signal(struct cv *cvp)
+{
+
+	KASSERT(cvp != NULL, ("%s: cvp NULL", __FUNCTION__));
+	mtx_enter(&sched_lock, MTX_SPIN);
+	if (!TAILQ_EMPTY(&cvp->cv_waitq)) {
+		CV_SIGNAL_VALIDATE(cvp);
+		cv_wakeup(cvp);
+	}
+	mtx_exit(&sched_lock, MTX_SPIN);
+}
+
+/*
+ * Broadcast a signal to a condition variable.  Wakes up all waiting processes.
+ * Should be called with the same mutex as was passed to cv_wait held.
+ */
+void
+cv_broadcast(struct cv *cvp)
+{
+
+	KASSERT(cvp != NULL, ("%s: cvp NULL", __FUNCTION__));
+	mtx_enter(&sched_lock, MTX_SPIN);
+	CV_SIGNAL_VALIDATE(cvp);
+	while (!TAILQ_EMPTY(&cvp->cv_waitq))
+		cv_wakeup(cvp);
+	mtx_exit(&sched_lock, MTX_SPIN);
+}
+
+/*
+ * Remove a process from the wait queue of its condition variable.  This may be
+ * called externally.
+ */
+void
+cv_waitq_remove(struct proc *p)
+{
+	struct cv *cvp;
+
+	mtx_enter(&sched_lock, MTX_SPIN);
+	if ((cvp = p->p_wchan) != NULL && p->p_flag & P_CVWAITQ) {
+		TAILQ_REMOVE(&cvp->cv_waitq, p, p_slpq);
+		p->p_flag &= ~P_CVWAITQ;
+		p->p_wchan = NULL;
+	}
+	mtx_exit(&sched_lock, MTX_SPIN);
+}
+
+/*
+ * Timeout function for cv_timedwait.  Put the process on the runqueue and set
+ * its timeout flag.
+ */
+static void
+cv_timedwait_end(void *arg)
+{
+	struct proc *p;
+
+	p = arg;
+	CTR3(KTR_PROC, "cv_timedwait_end: proc %p (pid %d, %s)", p, p->p_pid,
+	    p->p_comm);
+	mtx_enter(&sched_lock, MTX_SPIN);
+	if (p->p_wchan != NULL) {
+		if (p->p_stat == SSLEEP)
+			setrunnable(p);
+		else
+			cv_waitq_remove(p);
+		p->p_flag |= P_TIMEOUT;
+	}
+	mtx_exit(&sched_lock, MTX_SPIN);
+}