cpumask: Replace cpumask_of_cpu with cpumask_of_cpu_ptr

  * This patch replaces the dangerous lvalue version of cpumask_of_cpu
    with new cpumask_of_cpu_ptr macros.  These are patterned after the
    node_to_cpumask_ptr macros.

    In general terms, if there is a cpumask_of_cpu_map[] then a pointer to
    the cpumask_of_cpu_map[cpu] entry is used.  The cpumask_of_cpu_map
    is provided when there is a large NR_CPUS count, reducing
    greatly the amount of code generated and stack space used for
    cpumask_of_cpu().  The pointer to the cpumask_t value is needed for
    calling set_cpus_allowed_ptr() to reduce the amount of stack space
    needed to pass the cpumask_t value.

    If there isn't a cpumask_of_cpu_map[], then a temporary variable is
    declared and filled in with value from cpumask_of_cpu(cpu) as well as
    a pointer variable pointing to this temporary variable.  Afterwards,
    the pointer is used to reference the cpumask value.  The compiler
    will optimize out the extra dereference through the pointer as well
    as the stack space used for the pointer, resulting in identical code.

    A good example of the orthogonal usages is in net/sunrpc/svc.c:

	case SVC_POOL_PERCPU:
	{
		unsigned int cpu = m->pool_to[pidx];
		cpumask_of_cpu_ptr(cpumask, cpu);

		*oldmask = current->cpus_allowed;
		set_cpus_allowed_ptr(current, cpumask);
		return 1;
	}
	case SVC_POOL_PERNODE:
	{
		unsigned int node = m->pool_to[pidx];
		node_to_cpumask_ptr(nodecpumask, node);

		*oldmask = current->cpus_allowed;
		set_cpus_allowed_ptr(current, nodecpumask);
		return 1;
	}

Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 27 insertions, 5 deletions

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 80226e77614..2dbd9a287e7 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -62,6 +62,15 @@
  * int next_cpu_nr(cpu, mask)		Next cpu past 'cpu', or nr_cpu_ids
  *
  * cpumask_t cpumask_of_cpu(cpu)	Return cpumask with bit 'cpu' set
+ *ifdef CONFIG_HAS_CPUMASK_OF_CPU
+ * cpumask_of_cpu_ptr_declare(v)	Declares cpumask_t *v
+ * cpumask_of_cpu_ptr_next(v, cpu)	Sets v = &cpumask_of_cpu_map[cpu]
+ * cpumask_of_cpu_ptr(v, cpu)		Combines above two operations
+ *else
+ * cpumask_of_cpu_ptr_declare(v)	Declares cpumask_t _v and *v = &_v
+ * cpumask_of_cpu_ptr_next(v, cpu)	Sets _v = cpumask_of_cpu(cpu)
+ * cpumask_of_cpu_ptr(v, cpu)		Combines above two operations
+ *endif
  * CPU_MASK_ALL				Initializer - all bits set
  * CPU_MASK_NONE			Initializer - no bits set
  * unsigned long *cpus_addr(mask)	Array of unsigned long's in mask
@@ -236,11 +245,16 @@ static inline void __cpus_shift_left(cpumask_t *dstp,
 
 #ifdef CONFIG_HAVE_CPUMASK_OF_CPU_MAP
 extern cpumask_t *cpumask_of_cpu_map;
-#define cpumask_of_cpu(cpu)    (cpumask_of_cpu_map[cpu])
-
+#define cpumask_of_cpu(cpu)	(cpumask_of_cpu_map[cpu])
+#define	cpumask_of_cpu_ptr(v, cpu)					\
+		const cpumask_t *v = &cpumask_of_cpu(cpu)
+#define	cpumask_of_cpu_ptr_declare(v)					\
+		const cpumask_t *v
+#define cpumask_of_cpu_ptr_next(v, cpu)					\
+					v = &cpumask_of_cpu(cpu)
 #else
 #define cpumask_of_cpu(cpu)						\
-(*({									\
+({									\
 	typeof(_unused_cpumask_arg_) m;					\
 	if (sizeof(m) == sizeof(unsigned long)) {			\
 		m.bits[0] = 1UL<<(cpu);					\
@@ -248,8 +262,16 @@ extern cpumask_t *cpumask_of_cpu_map;
 		cpus_clear(m);						\
 		cpu_set((cpu), m);					\
 	}								\
-	&m;								\
-}))
+	m;								\
+})
+#define	cpumask_of_cpu_ptr(v, cpu) 					\
+		cpumask_t _##v = cpumask_of_cpu(cpu);			\
+		const cpumask_t *v = &_##v
+#define	cpumask_of_cpu_ptr_declare(v)					\
+		cpumask_t _##v;						\
+		const cpumask_t *v = &_##v
+#define cpumask_of_cpu_ptr_next(v, cpu)					\
+					_##v = cpumask_of_cpu(cpu)
 #endif
 
 #define CPU_MASK_LAST_WORD BITMAP_LAST_WORD_MASK(NR_CPUS)