linux-kernel - [PATCH] mm: forward declare struct rcuwait together with rcuwait_wake

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Message-Id: <20250916-mm-rcuwait-v1-1-39a3beea6ec3@linutronix.de>
Date: Tue, 16 Sep 2025 15:59:08 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 Suren Baghdasaryan <surenb@...gle.com>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
 Vlastimil Babka <vbabka@...e.cz>, Shakeel Butt <shakeel.butt@...ux.dev>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH] mm: forward declare struct rcuwait together with
 rcuwait_wake_up()

At the point of the forward declaration of rcuwait_wake_up()
in mmap_lock.h 'struct rcuwait' may have not yet been declared,
leading to compiler errors.

Add an explicit forward declaration for the struct.

Fixes: 75404e07663b ("mm: move mmap/vma locking logic into specific files")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
---
This doesn't seem to break any in-tree code right now.
I stumbled upon it while building a series for the next cycle.
Instead of putting this fix into my series and spamming all the mm
maintainers with it, maybe this could be part of the last mm bugfix pull
for this cycle.
---
 include/linux/mmap_lock.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 11a078de9150df1beff4f0bfb16e199333767614..9792dd4fff0ff73829833aae8ea3229a31757d61 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -3,6 +3,7 @@
 #define _LINUX_MMAP_LOCK_H

 /* Avoid a dependency loop by declaring here. */
+struct rcuwait;
 extern int rcuwait_wake_up(struct rcuwait *w);

 #include <linux/lockdep.h>

---
base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
change-id: 20250916-mm-rcuwait-03c5fe95f36d

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh@...utronix.de>