futex: Use RCU_INIT_POINTER() in futex_mm_init().

There is no need for an explicit NULL pointer initialisation plus a
comment why it is okay. RCU_INIT_POINTER() can be used for NULL
initialisations and it is documented.

This has been build tested with gcc version 9.3.0 (Debian 9.3.0-22) on a
x86-64 defconfig.

Fixes: 094ac8cff7858 ("futex: Relax the rcu_assign_pointer() assignment of mm->futex_phash in futex_mm_init()")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250517151455.1065363-4-bigeasy@linutronix.de

diff --git a/include/linux/futex.h b/include/linux/futex.h
index 168ffd5996b4808491c05bdc7c8d0aeca1d37ee5..005b040c4791bb12feae66476dbee66dc8b8df07 100644 (file)
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -88,14 +88,7 @@ void futex_hash_free(struct mm_struct *mm);
 
 static inline void futex_mm_init(struct mm_struct *mm)
 {
-       /*
-        * No need for rcu_assign_pointer() here, as we can rely on
-        * tasklist_lock write-ordering in copy_process(), before
-        * the task's MM becomes visible and the ->futex_phash
-        * becomes externally observable:
-        */
-       mm->futex_phash = NULL;
-
+       RCU_INIT_POINTER(mm->futex_phash, NULL);
        mutex_init(&mm->futex_hash_lock);
 }