cpumask: Use all NR_CPUS bits unless CONFIG_CPUMASK_OFFSTACK

Impact: futureproof as we convert more code to new APIs

The old cpumask operators treat all NR_CPUS bits as relevent, the new
ones use nr_cpumask_bits.  For large NR_CPUS and small nr_cpu_ids, this
makes a difference.

However, mixing the two can cause problems with undefined bits.  An
arch which sets CONFIG_CPUMASK_OFFSTACK should have converted across
to the new operators, so it's safe in that case.

(Thanks to Stephen Rothwell for bisecting the initial unused-bits bug,
and Mike Travis for this solution).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Mike Travis <travis@sgi.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 94a2ab88ae85..d4bf52603e6b 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -510,9 +510,6 @@ extern cpumask_t cpu_active_map;
         [BITS_TO_LONGS(NR_CPUS)-1] = CPU_MASK_LAST_WORD \
 }
 
-/* This produces more efficient code. */
-#define nr_cpumask_bits NR_CPUS
-
 #else /* NR_CPUS > BITS_PER_LONG */
 
 #define CPU_BITS_ALL                                            \
@@ -520,9 +517,15 @@ extern cpumask_t cpu_active_map;
         [0 ... BITS_TO_LONGS(NR_CPUS)-2] = ~0UL,                \
         [BITS_TO_LONGS(NR_CPUS)-1] = CPU_MASK_LAST_WORD         \
 }
+#endif /* NR_CPUS > BITS_PER_LONG */
 
+#ifdef CONFIG_CPUMASK_OFFSTACK
+/* Assuming NR_CPUS is huge, a runtime limit is more efficient.  Also,
+ * not all bits may be allocated. */
 #define nr_cpumask_bits nr_cpu_ids
-#endif /* NR_CPUS > BITS_PER_LONG */
+#else
+#define nr_cpumask_bits NR_CPUS
+#endif
 
 /* verify cpu argument to cpumask_* operators */
 static inline unsigned int cpumask_check(unsigned int cpu)