cpumask: zero extra bits in alloc_cpumask_var_node

Impact: extra safety checks during transition

When CONFIG_CPUMASKS_OFFSTACK is set, the new cpumask_ operators only
use bits up to nr_cpu_ids, not NR_CPUS.  Using the old cpus_ operators
on these masks can mean accessing undefined bits.

After some discussion, Mike and I decided to err on the side of caution;
we zero the "undefined" bits in alloc_cpumask_var_node() until all the
old cpumask functions are removed.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/lib/cpumask.c b/lib/cpumask.c
index 8e1496c..3389e24 100644 (file)
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -107,6 +107,14 @@ 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 int tail;
+               tail = BITS_TO_LONGS(NR_CPUS - nr_cpumask_bits) * sizeof(long);
+               memset(cpumask_bits(*mask) + cpumask_size() - tail,
+                      0, tail);
+       }
+
        return *mask != NULL;
 }
 EXPORT_SYMBOL(alloc_cpumask_var_node);