linux-kernel - [PATCH] fs: use a consume fence in mnt

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Message-ID: <20241130051712.1036527-1-mjguzik@gmail.com>
Date: Sat, 30 Nov 2024 06:17:11 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: brauner@...nel.org
Cc: viro@...iv.linux.org.uk,
	jack@...e.cz,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH] fs: use a consume fence in mnt_idmap()

The routine is used in link_path_walk() for every path component.

To my reading the entire point of the fence was to grab a fully
populated mnt_idmap, but that's already going to happen with mere
consume fence.

Eliminates an actual fence on arm64.

Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
---
 include/linux/mount.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/mount.h b/include/linux/mount.h
index c34c18b4e8f3..33f17b6e8732 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -76,7 +76,7 @@ struct vfsmount {
 static inline struct mnt_idmap *mnt_idmap(const struct vfsmount *mnt)
 {
 	/* Pairs with smp_store_release() in do_idmap_mount(). */
-	return smp_load_acquire(&mnt->mnt_idmap);
+	return READ_ONCE(mnt->mnt_idmap);
 }
 
 extern int mnt_want_write(struct vfsmount *mnt);
-- 
2.43.0