cpumask: only allocate nr_cpumask_bits.

Now we'll find out the hard way if anyone has CPUMASK_OFFSTACK and is
returning these or assigning them.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

include/linux/cpumask.h

@@ -11,6 +11,7 @@
 #include <linux/bitmap.h>
 #include <linux/bug.h>
 
+/* Don't assign or return these: may not be this big! */
 typedef struct cpumask { DECLARE_BITMAP(bits, NR_CPUS); } cpumask_t;
 
 /**
@@ -609,9 +610,7 @@ static inline int cpulist_parse(const char *buf, struct cpumask *dstp)
  */
 static inline size_t cpumask_size(void)
 {
-	/* FIXME: Once all cpumask assignments are eliminated, this
-	 * can be nr_cpumask_bits */
-	return BITS_TO_LONGS(NR_CPUS) * sizeof(long);
+	return BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long);
 }
 
 /*

lib/cpumask.c

@@ -89,13 +89,6 @@ bool alloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node)
 		dump_stack();
 	}
 #endif
-	/* FIXME: Bandaid to save us from old primitives which go to NR_CPUS. */
-	if (*mask) {
-		unsigned char *ptr = (unsigned char *)cpumask_bits(*mask);
-		unsigned int tail;
-		tail = BITS_TO_LONGS(NR_CPUS - nr_cpumask_bits) * sizeof(long);
-		memset(ptr + cpumask_size() - tail, 0, tail);
-	}
 
 	return *mask != NULL;
 }