[Xen-devel] [PATCH] Trivial fix for latent bug in page_alloc.c

[Rusty Russell <rusty@xxxxxxxxxxxxxxx>]

Was reading through page_alloc.c, and the "find smallest order" loop
assumes MIN_ORDER is 0.  Easiest fix is to get rid of "MIN_ORDER" and
hence NR_ORDERS, and simplify code.

Rusty.

--- xen/common/page_alloc.c.~1~ 2005-01-11 15:35:54.000000000 +1100
+++ xen/common/page_alloc.c     2005-01-19 14:51:47.000000000 +1100
@@ -203,10 +203,8 @@
 #define NR_ZONES    2
 
 /* Up to 2^10 pages can be allocated at once. */
-#define MIN_ORDER  0
 #define MAX_ORDER 10
-#define NR_ORDERS (MAX_ORDER - MIN_ORDER + 1)
-static struct list_head heap[NR_ZONES][NR_ORDERS];
+static struct list_head heap[NR_ZONES][MAX_ORDER];
 
 static unsigned long avail[NR_ZONES];
 
@@ -220,7 +218,7 @@
     memset(avail, 0, sizeof(avail));
 
     for ( i = 0; i < NR_ZONES; i++ )
-        for ( j = 0; j < NR_ORDERS; j++ )
+        for ( j = 0; j < MAX_ORDER; j++ )
             INIT_LIST_HEAD(&heap[i][j]);
 
     /* Pages that are free now go to the domain sub-allocator. */
@@ -251,17 +249,18 @@
     int i;
     struct pfn_info *pg;
 
-    if ( unlikely(order < MIN_ORDER) || unlikely(order > MAX_ORDER) )
+    ASSERT(order >= 0);
+    if ( unlikely(order >= MAX_ORDER) )
         return NULL;
 
     spin_lock(&heap_lock);
 
     /* Find smallest order which can satisfy the request. */
-    for ( i = order; i < NR_ORDERS; i++ )
+    for ( i = order; i < MAX_ORDER; i++ )
        if ( !list_empty(&heap[zone][i]) )
            break;
 
-    if ( i == NR_ORDERS ) 
+    if ( i == MAX_ORDER ) 
         goto no_memory;
  
     pg = list_entry(heap[zone][i].next, struct pfn_info, list);

-- 
A bad analogy is like a leaky screwdriver -- Richard Braakman



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