[PATCH] Memoryless nodes: use "node_memory_map" for cpuset mems_allowed validation

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

This fixes a problem I encountered testing Christoph's memoryless nodes
series.  Applies atop that series.  Other than this, series holds up
under what testing I've been able to do this week.

Memoryless Nodes:  use "node_memory_map" for cpusets mems_allowed validation

cpusets try to ensure that any node added to a cpuset's 
mems_allowed is on-line and contains memory.  The assumption
was that online nodes contained memory.  Thus, it is possible
to add memoryless nodes to a cpuset and then add tasks to this
cpuset.  This results in continuous series of oom-kill and other
console stack traces and apparent system hang.

Change cpusets to use node_states[N_MEMORY] [a.k.a.
node_memory_map] in place of node_online_map when vetting 
memories.  Return error if admin attempts to write a non-empty
mems_allowed node mask containing only memoryless-nodes.

Signed-off-by:  Lee Schermerhorn <lee.schermerhorn@hp.com>

 kernel/cpuset.c |   33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

Index: Linux/kernel/cpuset.c
===================================================================
--- Linux.orig/kernel/cpuset.c	2007-07-20 16:02:01.000000000 -0400
+++ Linux/kernel/cpuset.c	2007-07-20 16:27:46.000000000 -0400
@@ -316,26 +316,26 @@ static void guarantee_online_cpus(const 
 
 /*
  * Return in *pmask the portion of a cpusets's mems_allowed that
- * are online.  If none are online, walk up the cpuset hierarchy
- * until we find one that does have some online mems.  If we get
- * all the way to the top and still haven't found any online mems,
- * return node_online_map.
+ * are online, with memory.  If none are online with memory, walk
+ * up the cpuset hierarchy until we find one that does have some
+ * online mems.  If we get all the way to the top and still haven't
+ * found any online mems, return node_states[N_MEMORY].
  *
  * One way or another, we guarantee to return some non-empty subset
- * of node_online_map.
+ * of node_states[N_MEMORY].
  *
  * Call with callback_mutex held.
  */
 
 static void guarantee_online_mems(const struct cpuset *cs, nodemask_t *pmask)
 {
-	while (cs && !nodes_intersects(cs->mems_allowed, node_online_map))
+	while (cs && !nodes_intersects(cs->mems_allowed, node_states[N_MEMORY]))
 		cs = cs->parent;
 	if (cs)
-		nodes_and(*pmask, cs->mems_allowed, node_online_map);
+		nodes_and(*pmask, cs->mems_allowed, node_states[N_MEMORY]);
 	else
-		*pmask = node_online_map;
-	BUG_ON(!nodes_intersects(*pmask, node_online_map));
+		*pmask = node_states[N_MEMORY];
+	BUG_ON(!nodes_intersects(*pmask, node_states[N_MEMORY]));
 }
 
 /**
@@ -623,8 +623,21 @@ static int update_nodemask(struct cpuset
 		retval = nodelist_parse(buf, trialcs.mems_allowed);
 		if (retval < 0)
 			goto done;
+		if (!nodes_intersects(trialcs.mems_allowed,
+						node_states[N_MEMORY])) {
+			/*
+			 * error if only memoryless nodes specified.
+			 */
+			retval = -ENOSPC;
+			goto done;
+		}
 	}
-	nodes_and(trialcs.mems_allowed, trialcs.mems_allowed, node_online_map);
+	/*
+	 * Exclude memoryless nodes.  We know that trialcs.mems_allowed
+	 * contains at least one node with memory.
+	 */
+	nodes_and(trialcs.mems_allowed, trialcs.mems_allowed,
+						node_states[N_MEMORY]);
 	oldmem = cs->mems_allowed;
 	if (nodes_equal(oldmem, trialcs.mems_allowed)) {
 		retval = 0;		/* Too easy - nothing to do */


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