From d1d9d4e5f8f9ac1d22e1258759d6ee9e49c7fe90 Mon Sep 17 00:00:00 2001
From: Egbert Eich <eich@freedesktop.org>
Date: Fri, 9 Apr 2010 15:10:32 +0200
Subject: [PATCH] Prevent XSync Alarms from senslessly calling CheckTrigger() when inactive.

If an XSync Alarm is set to inactive there is no need to check if a trigger
needs to fire. Doing so if the counter is the IdleCounter will put the
server on 100 percent CPU load since the select timeout is set to 0.
---
 xorg-server-1.8.0/Xext/sync.c    |   11 +++++++++--
 xorg-server-1.8.0/Xext/syncsrv.h |    1 +
 2 files changed, 10 insertions(+), 2 deletions(-)

Index: xorg-server-1.8.0/Xext/sync.c
===================================================================
--- xorg-server-1.8.0.orig/Xext/sync.c
+++ xorg-server-1.8.0/Xext/sync.c
@@ -518,6 +518,10 @@ SyncAlarmTriggerFired(SyncTrigger *pTrig
 	    pAlarm->state = XSyncAlarmInactive;
 	}
     }
+    /* Stop server from looping! */
+    if (pAlarm->state == XSyncAlarmInactive)
+	SyncDeleteTriggerFromCounter(&pAlarm->trigger);
+
     /*  The AlarmNotify event has to have the "new state of the alarm"
      *  which we can't be sure of until this point.  However, it has
      *  to have the "old" trigger test value.  That's the reason for
@@ -730,7 +734,7 @@ SyncChangeAlarmAttributes(ClientPtr clie
     XSyncCounter   counter;
     Mask	   origmask = mask;
 
-    counter = pAlarm->trigger.pCounter ? pAlarm->trigger.pCounter->id : None;
+    counter = pAlarm->counter_id;
 
     while (mask)
     {
@@ -741,7 +745,7 @@ SyncChangeAlarmAttributes(ClientPtr clie
 	  case XSyncCACounter:
 	    mask &= ~XSyncCACounter;
 	    /* sanity check in SyncInitTrigger */
-	    counter = *values++;
+	    counter = pAlarm->counter_id = *values++;
 	    break;
 
 	  case XSyncCAValueType:
@@ -808,6 +812,14 @@ SyncChangeAlarmAttributes(ClientPtr clie
 	    return BadMatch;
 	}
     }
+    if (pAlarm->state == XSyncAlarmInactive) {
+	/*
+	 * If we are inactive the trigger has been deleted from the counter.
+	 * Persuade SyncInitTrigger() to readd it.
+	 */
+	origmask |= XSyncCACounter;
+	pAlarm->trigger.pCounter = NULL;
+    }
 
     /* postpone this until now, when we're sure nothing else can go wrong */
     if ((status = SyncInitTrigger(client, &pAlarm->trigger, counter,
@@ -815,6 +827,7 @@ SyncChangeAlarmAttributes(ClientPtr clie
 	return status;
 
     /* XXX spec does not really say to do this - needs clarification */
+    /* It's the only place where it is set to XSyncAlarmActive! */
     pAlarm->state = XSyncAlarmActive;
     return Success;
 }
@@ -1617,8 +1630,10 @@ ProcSyncCreateAlarm(ClientPtr client)
 
     pAlarm->client = client;
     pAlarm->alarm_id = stuff->id;
+    pAlarm->counter_id = None;
     XSyncIntToValue(&pAlarm->delta, 1L);
     pAlarm->events = TRUE;
+    /* SyncChangeAlarmAttributes() changes this - no need to set this here! */
     pAlarm->state = XSyncAlarmInactive;
     pAlarm->pEventClients = NULL;
     status = SyncChangeAlarmAttributes(client, pAlarm, vmask,
Index: xorg-server-1.8.0/Xext/syncsrv.h
===================================================================
--- xorg-server-1.8.0.orig/Xext/syncsrv.h
+++ xorg-server-1.8.0/Xext/syncsrv.h
@@ -129,6 +129,7 @@ typedef struct _SyncAlarm {
     int		events;
     int		state;
     SyncAlarmClientList *pEventClients;
+    XSyncCounter counter_id;
 } SyncAlarm;
 
 typedef struct {