From 9c043d590896a77d5d66b978a963573a41d66ad3 Mon Sep 17 00:00:00 2001
From: jh <jh@FreeBSD.org>
Date: Mon, 22 Nov 2010 16:47:53 +0000
Subject: Use g_eventlock to protect against losing wakeups in the g_event
 process and replace tsleep(9) with msleep(9) which doesn't use a timeout. The
 previously used timeout caused the event process to wake up ten times per
 second on an idle system.
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one_event() is now called with the topology lock held and it returns
with both the topology and event locks held when there are no more
events in the queue.

Reported by:	mav, Marius Nünnerich
Reviewed by:	freebsd-geom
---
 sys/geom/geom_event.c | 63 ++++++++++++++++++++++++++++-----------------------
 sys/geom/geom_kern.c  |  6 ++---
 2 files changed, 37 insertions(+), 32 deletions(-)

diff --git a/sys/geom/geom_event.c b/sys/geom/geom_event.c
index 44890aa..d6e5498 100644
--- a/sys/geom/geom_event.c
+++ b/sys/geom/geom_event.c
@@ -183,33 +183,27 @@ one_event(void)
 	struct g_event *ep;
 	struct g_provider *pp;
 
-	g_topology_lock();
-	for (;;) {
-		mtx_lock(&g_eventlock);
-		TAILQ_FOREACH(pp, &g_doorstep, orphan) {
-			if (pp->nstart == pp->nend)
-				break;
-		}
-		if (pp != NULL) {
-			G_VALID_PROVIDER(pp);
-			TAILQ_REMOVE(&g_doorstep, pp, orphan);
-		}
-		mtx_unlock(&g_eventlock);
-		if (pp == NULL)
+	g_topology_assert();
+	mtx_lock(&g_eventlock);
+	TAILQ_FOREACH(pp, &g_doorstep, orphan) {
+		if (pp->nstart == pp->nend)
 			break;
+	}
+	if (pp != NULL) {
+		G_VALID_PROVIDER(pp);
+		TAILQ_REMOVE(&g_doorstep, pp, orphan);
+		mtx_unlock(&g_eventlock);
 		g_orphan_register(pp);
+		return (1);
 	}
-	mtx_lock(&g_eventlock);
+
 	ep = TAILQ_FIRST(&g_events);
 	if (ep == NULL) {
 		wakeup(&g_pending_events);
-		mtx_unlock(&g_eventlock);
-		g_topology_unlock();
 		return (0);
 	}
 	if (ep->flag & EV_INPROGRESS) {
 		mtx_unlock(&g_eventlock);
-		g_topology_unlock();
 		return (1);
 	}
 	ep->flag |= EV_INPROGRESS;
@@ -228,7 +222,6 @@ one_event(void)
 		mtx_unlock(&g_eventlock);
 		g_free(ep);
 	}
-	g_topology_unlock();
 	return (1);
 }
 
@@ -237,16 +230,27 @@ g_run_events()
 {
 	int i;
 
-	while (one_event())
-		;
-	g_topology_lock();
-	i = g_wither_work;
-	while (i) {
-		i = g_wither_washer();
-		g_wither_work = i & 1;
-		i &= 2;
+	for (;;) {
+		g_topology_lock();
+		while (one_event())
+			;
+		mtx_assert(&g_eventlock, MA_OWNED);
+		i = g_wither_work;
+		if (i) {
+			mtx_unlock(&g_eventlock);
+			while (i) {
+				i = g_wither_washer();
+				g_wither_work = i & 1;
+				i &= 2;
+			}
+			g_topology_unlock();
+		} else {
+			g_topology_unlock();
+			msleep(&g_wait_event, &g_eventlock, PRIBIO | PDROP,
+			    "-", 0);
+		}
 	}
-	g_topology_unlock();
+	/* NOTREACHED */
 }
 
 void
@@ -338,9 +342,12 @@ g_post_event(g_event_t *func, void *arg, int flag, ...)
 }
 
 void
-g_do_wither() {
+g_do_wither()
+{
 
+	mtx_lock(&g_eventlock);
 	g_wither_work = 1;
+	mtx_unlock(&g_eventlock);
 	wakeup(&g_wait_event);
 }
 
diff --git a/sys/geom/geom_kern.c b/sys/geom/geom_kern.c
index fc4e245..5e7e274 100644
--- a/sys/geom/geom_kern.c
+++ b/sys/geom/geom_kern.c
@@ -137,10 +137,8 @@ g_event_procbody(void)
 	thread_lock(tp);
 	sched_prio(tp, PRIBIO);
 	thread_unlock(tp);
-	for(;;) {
-		g_run_events();
-		tsleep(&g_wait_event, PRIBIO, "-", hz/10);
-	}
+	g_run_events();
+	/* NOTREACHED */
 }
 
 static struct kproc_desc g_event_kp = {
-- 
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