fs: ensure that internal tmpfs mount gets mount id zero

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@kernel.org
Fixes: 7f9bfafc5f49 ("fs: use xarray for old mount id")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index c58674a20cad54a9d015cbea1928d7725c8b07cf..8b082b1de7f3ec6b1b0f787cffed59261fef75f9 100644 (file)
--- 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);