[PATCH v12 8/9] cpumask: Add initialiser CPUMASK_NULL to use cleanup helpers

[Gabriele Monaco <gmonaco@redhat.com>]

The cleanup helper __free(free_cpumask_var) works only if the function
returns after alloc_cpumask_var, this can complicate the code in case
there are multiple cpumasks using the cleanup helper.

Define a cpumask initialiser that is NULL if the cpumask is a pointer
and {} if it's on stack. This allows users of the cleanup helper to use
it freely on initialised cpumasks as the actual free will be called only
if the mask is not NULL (and of course if it's a pointer).

This solution was first used in [1], dropped as eventually a single mask
was sufficient.

[1] - https://lore.kernel.org/lkml/20240120025053.684838-8-yury.norov@gmail.com

Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
---
 include/linux/cpumask.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index ff8f41ab7ce6..5fb9c3fe4256 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -1005,6 +1005,7 @@ static __always_inline unsigned int cpumask_size(void)
 
 #define this_cpu_cpumask_var_ptr(x)	this_cpu_read(x)
 #define __cpumask_var_read_mostly	__read_mostly
+#define CPUMASK_NULL			NULL
 
 bool alloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node);
 
@@ -1051,6 +1052,7 @@ static __always_inline bool cpumask_available(cpumask_var_t mask)
 
 #define this_cpu_cpumask_var_ptr(x) this_cpu_ptr(x)
 #define __cpumask_var_read_mostly
+#define CPUMASK_NULL {}
 
 static __always_inline bool alloc_cpumask_var(cpumask_var_t *mask, gfp_t flags)
 {
-- 
2.51.0