[PATCH 6.18.y 1/2] futex: Make futex_mm_init() void

[Sasha Levin <sashal@kernel.org>]

From: Thomas Gleixner <tglx@kernel.org>

[ Upstream commit d7b3f52c861f54ba2fff15696d3798277fb4c19f ]

Nothing fails there. Mop up the leftovers of the early version of this,
which did an allocation.

While at it clean up the stubs and the #ifdef comments to make the header
file readable.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260602090535.356789395@kernel.org
Stable-dep-of: 1c7efabfbaf7 ("futex: Avoid private hash use-after-free on final put")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/futex.h | 28 +++++++++++-----------------
 kernel/fork.c         |  8 ++------
 kernel/futex/core.c   |  3 +--
 3 files changed, 14 insertions(+), 25 deletions(-)

diff --git a/include/linux/futex.h b/include/linux/futex.h
index 9e9750f049805..87559766319e1 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -85,22 +85,20 @@ int futex_hash_prctl(unsigned long arg2, unsigned long arg3, unsigned long arg4)
 #ifdef CONFIG_FUTEX_PRIVATE_HASH
 int futex_hash_allocate_default(void);
 void futex_hash_free(struct mm_struct *mm);
-int futex_mm_init(struct mm_struct *mm);
-
-#else /* !CONFIG_FUTEX_PRIVATE_HASH */
+void futex_mm_init(struct mm_struct *mm);
+#else  /* CONFIG_FUTEX_PRIVATE_HASH */
 static inline int futex_hash_allocate_default(void) { return 0; }
 static inline int futex_hash_free(struct mm_struct *mm) { return 0; }
-static inline int futex_mm_init(struct mm_struct *mm) { return 0; }
-#endif /* CONFIG_FUTEX_PRIVATE_HASH */
+static inline void futex_mm_init(struct mm_struct *mm) { }
+#endif /* !CONFIG_FUTEX_PRIVATE_HASH */
 
-#else /* !CONFIG_FUTEX */
+#else  /* CONFIG_FUTEX */
 static inline void futex_init_task(struct task_struct *tsk) { }
 static inline void futex_exit_recursive(struct task_struct *tsk) { }
 static inline void futex_exit_release(struct task_struct *tsk) { }
 static inline void futex_exec_release(struct task_struct *tsk) { }
-static inline long do_futex(u32 __user *uaddr, int op, u32 val,
-			    ktime_t *timeout, u32 __user *uaddr2,
-			    u32 val2, u32 val3)
+static inline long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
+			    u32 __user *uaddr2, u32 val2, u32 val3)
 {
 	return -EINVAL;
 }
@@ -108,13 +106,9 @@ static inline int futex_hash_prctl(unsigned long arg2, unsigned long arg3, unsig
 {
 	return -EINVAL;
 }
-static inline int futex_hash_allocate_default(void)
-{
-	return 0;
-}
+static inline int futex_hash_allocate_default(void) { return 0; }
 static inline int futex_hash_free(struct mm_struct *mm) { return 0; }
-static inline int futex_mm_init(struct mm_struct *mm) { return 0; }
+static inline void futex_mm_init(struct mm_struct *mm) { }
+#endif /* !CONFIG_FUTEX */
 
-#endif
-
-#endif
+#endif /* _LINUX_FUTEX_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index 91f1512a1d312..ccddeba6790a4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1062,6 +1062,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 #endif
 	mm_init_uprobes_state(mm);
 	hugetlb_count_init(mm);
+	futex_mm_init(mm);
 
 	mm_flags_clear_all(mm);
 	if (current->mm) {
@@ -1074,11 +1075,8 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 		mm->def_flags = 0;
 	}
 
-	if (futex_mm_init(mm))
-		goto fail_mm_init;
-
 	if (mm_alloc_pgd(mm))
-		goto fail_nopgd;
+		goto fail_mm_init;
 
 	if (mm_alloc_id(mm))
 		goto fail_noid;
@@ -1105,8 +1103,6 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 	mm_free_id(mm);
 fail_noid:
 	mm_free_pgd(mm);
-fail_nopgd:
-	futex_hash_free(mm);
 fail_mm_init:
 	free_mm(mm);
 	return NULL;
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index fde558fd2bd60..f43d8c9e28a66 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -1747,7 +1747,7 @@ static bool futex_ref_is_dead(struct futex_private_hash *fph)
 	return atomic_long_read(&mm->futex_atomic) == 0;
 }
 
-int futex_mm_init(struct mm_struct *mm)
+void futex_mm_init(struct mm_struct *mm)
 {
 	mutex_init(&mm->futex_hash_lock);
 	RCU_INIT_POINTER(mm->futex_phash, NULL);
@@ -1756,7 +1756,6 @@ int futex_mm_init(struct mm_struct *mm)
 	mm->futex_ref = NULL;
 	atomic_long_set(&mm->futex_atomic, 0);
 	mm->futex_batches = get_state_synchronize_rcu();
-	return 0;
 }
 
 void futex_hash_free(struct mm_struct *mm)
-- 
2.53.0