[PATCH 6.19 564/844] fs: ensure that internal tmpfs mount gets mount id zero

[Sasha Levin]

From: Christian Brauner <brauner@xxxxxxxxxx>

[ Upstream commit a2062463e894039a6fdc2334b96afd91d44b64a8 ]

and the rootfs get mount id one as it always has. Before we actually
mount the rootfs we create an internal tmpfs mount which has mount id
zero but is never exposed anywhere. Continue that "tradition".

Link: https://patch.msgid.link/20260112-work-immutable-rootfs-v2-1-88dd1c34a204@xxxxxxxxxx
Fixes: 7f9bfafc5f49 ("fs: use xarray for old mount id")
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/namespace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index f6879f282daec..ecf0e72ce6cfd 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -221,7 +221,7 @@ static int mnt_alloc_id(struct mount *mnt)
 	int res;
 
 	xa_lock(&mnt_id_xa);
-	res = __xa_alloc(&mnt_id_xa, &mnt->mnt_id, mnt, XA_LIMIT(1, INT_MAX), GFP_KERNEL);
+	res = __xa_alloc(&mnt_id_xa, &mnt->mnt_id, mnt, xa_limit_31b, GFP_KERNEL);
 	if (!res)
 		mnt->mnt_id_unique = ++mnt_id_ctr;
 	xa_unlock(&mnt_id_xa);
-- 
2.51.0