[Xen-devel] [PATCH] Fix hypervisor crash with unpopulated NUMA nodes

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi Keir,

on NUMA systems with memory-less nodes Xen crashes quite early in the 
hypervisor (while initializing the heaps). This is not an issue if this 
happens to be the last node, but "inner" nodes trigger this reliably.
On multi-node processors it is much more likely to leave a node unequipped.
The attached patch fixes this by enumerating the node via the 
node_online_map instead of counting from 0 to num_nodes.
The resulting NUMA setup is still somewhat strange, but at least it does 
not crash. In lowlevel/xc/xc.c there is again this enumeration bug, but 
I suppose we cannot access the HV's node_online_map from this context, 
so the xm info output is not correct (but xm debug-keys H is).
I plan to rework the handling of memory-less nodes later.

Please also consider committing this to the -testing trees.

Regards,
Andre.

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>

--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448 3567 12
----to satisfy European Law for business letters:
Advanced Micro Devices GmbH
Karl-Hammerschmidt-Str. 34, 85609 Dornach b. Muenchen
Geschaeftsfuehrer: Andrew Bowd; Thomas M. McCoy; Giuliano Meroni
Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen
Registergericht Muenchen, HRB Nr. 43632

diff -r 440d22c01652 xen/common/page_alloc.c
--- a/xen/common/page_alloc.c   Wed Oct 07 08:07:06 2009 +0100
+++ b/xen/common/page_alloc.c   Wed Oct 07 11:40:54 2009 +0200
@@ -294,7 +294,6 @@
         node = cpu_to_node(smp_processor_id());
 
     ASSERT(node >= 0);
-    ASSERT(node < num_nodes);
     ASSERT(zone_lo <= zone_hi);
     ASSERT(zone_hi < NR_ZONES);
 
@@ -323,8 +322,9 @@
         } while ( zone-- > zone_lo ); /* careful: unsigned zone may wrap */
 
         /* Pick next node, wrapping around if needed. */
-        if ( ++node == num_nodes )
-            node = 0;
+        node = next_node(node, node_online_map);
+        if (node == MAX_NUMNODES)
+            node = first_node(node_online_map);
     }
 
     /* Try to free memory from tmem */
@@ -466,7 +466,6 @@
 
     ASSERT(order <= MAX_ORDER);
     ASSERT(node >= 0);
-    ASSERT(node < num_online_nodes());
 
     for ( i = 0; i < (1 << order); i++ )
     {
@@ -817,13 +816,13 @@
 static unsigned long avail_heap_pages(
     unsigned int zone_lo, unsigned int zone_hi, unsigned int node)
 {
-    unsigned int i, zone, num_nodes = num_online_nodes();
+    unsigned int i, zone;
     unsigned long free_pages = 0;
 
     if ( zone_hi >= NR_ZONES )
         zone_hi = NR_ZONES - 1;
 
-    for ( i = 0; i < num_nodes; i++ )
+    for_each_online_node(i)
     {
         if ( !avail[i] )
             continue;

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