From 92f44a3f3c693167695ed564533c8b67cf76e142 Mon Sep 17 00:00:00 2001
From: Craig Rodrigues <rodrigc@FreeBSD.org>
Date: Mon, 12 Dec 2005 00:02:22 +0000
Subject: [PATCH] Contributions from XFS for FreeBSD project: - Implement
 cv_wait_unlock() method which has semantics compatible   with the sv_wait()
 method in IRIX.  For cv_wait_unlock(), the lock   must be held before
 entering the function, but is not held when the   function is exited.

- Implement the existing cv_wait() function in terms of cv_wait_unlock().

Submitted by:	kan
Feedback from:	jhb, trhodes, Christoph Hellwig <hch at infradead dot org>
---
 sys/kern/kern_condvar.c | 49 ++++++++++++++++++++++++++++-------------
 sys/sys/condvar.h       |  1 +
 2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/sys/kern/kern_condvar.c b/sys/kern/kern_condvar.c
index 8ccea3aab414..ede6b61373bf 100644
--- a/sys/kern/kern_condvar.c
+++ b/sys/kern/kern_condvar.c
@@ -95,17 +95,8 @@ cv_destroy(struct cv *cvp)
 void
 cv_wait(struct cv *cvp, struct mtx *mp)
 {
-	struct thread *td;
 	WITNESS_SAVE_DECL(mp);
 
-	td = curthread;
-#ifdef KTRACE
-	if (KTRPOINT(td, KTR_CSW))
-		ktrcsw(1, 0);
-#endif
-	CV_ASSERT(cvp, mp, td);
-	WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, &mp->mtx_object,
-	    "Waiting on \"%s\"", cvp->cv_description);
 	WITNESS_SAVE(&mp->mtx_object, mp);
 
 	if (cold || panicstr) {
@@ -118,6 +109,40 @@ cv_wait(struct cv *cvp, struct mtx *mp)
 		return;
 	}
 
+	cv_wait_unlock(cvp, mp);
+	mtx_lock(mp);
+	WITNESS_RESTORE(&mp->mtx_object, mp);
+}
+
+/*
+ * Wait on a condition variable.  This function differs from cv_wait by
+ * not aquiring the mutex after condition variable was signaled.
+ */
+void
+cv_wait_unlock(struct cv *cvp, struct mtx *mp)
+{
+	struct thread *td;
+
+	td = curthread;
+#ifdef KTRACE
+	if (KTRPOINT(td, KTR_CSW))
+		ktrcsw(1, 0);
+#endif
+	CV_ASSERT(cvp, mp, td);
+	WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, &mp->mtx_object,
+	    "Waiting on \"%s\"", cvp->cv_description);
+
+	if (cold || panicstr) {
+		/*
+		 * During autoconfiguration, just give interrupts
+		 * a chance, then just return.  Don't run any other
+		 * thread or panic below, in case this is the idle
+		 * process and already asleep.
+		 */
+		mtx_unlock(mp);
+		return;
+	}
+
 	sleepq_lock(cvp);
 
 	cvp->cv_waiters++;
@@ -127,13 +152,7 @@ cv_wait(struct cv *cvp, struct mtx *mp)
 	sleepq_add(cvp, mp, cvp->cv_description, SLEEPQ_CONDVAR);
 	sleepq_wait(cvp);
 
-#ifdef KTRACE
-	if (KTRPOINT(td, KTR_CSW))
-		ktrcsw(0, 0);
-#endif
 	PICKUP_GIANT();
-	mtx_lock(mp);
-	WITNESS_RESTORE(&mp->mtx_object, mp);
 }
 
 /*
diff --git a/sys/sys/condvar.h b/sys/sys/condvar.h
index a8c9db72c0b1..97f699ab3453 100644
--- a/sys/sys/condvar.h
+++ b/sys/sys/condvar.h
@@ -53,6 +53,7 @@ void	cv_init(struct cv *cvp, const char *desc);
 void	cv_destroy(struct cv *cvp);
 
 void	cv_wait(struct cv *cvp, struct mtx *mp);
+void	cv_wait_unlock(struct cv *cvp, struct mtx *mp);
 int	cv_wait_sig(struct cv *cvp, struct mtx *mp);
 int	cv_timedwait(struct cv *cvp, struct mtx *mp, int timo);
 int	cv_timedwait_sig(struct cv *cvp, struct mtx *mp, int timo);