From 4209cd7f546b55733d4d221109423600b025575a Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 2 Oct 2026 15:52:45 +0200 Subject: [PATCH] namespace: keep the private nullfs instance in knullfs The private nullfs instance that kernel threads are confined to is only ever reachable through init_task's root and pwd. The following patches point mounts at it as well, so keep it in a global. No functional changes. Link: https://patch.msgid.link/20261002-work-mount-fixes-4-v1-14-dd44b89d44ce@kernel.org Signed-off-by: Christian Brauner (Amutable) --- fs/mount.h | 1 + fs/namespace.c | 11 ++++++----- 2 files changed, 7 insertions(+), 5 deletions(-) diff --git a/fs/mount.h b/fs/mount.h index 2223fb141499..4e68e5cbc254 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -6,6 +6,7 @@ #include extern struct file_system_type nullfs_fs_type; +extern struct vfsmount *knullfs; extern struct list_head notify_list; struct mnt_namespace { diff --git a/fs/namespace.c b/fs/namespace.c index e116894c8667..d1e83cda57e6 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -80,6 +80,7 @@ static u64 mnt_id_ctr = MNT_UNIQUE_ID_OFFSET; static struct hlist_head *mount_hashtable __ro_after_init; static struct hlist_head *mountpoint_hashtable __ro_after_init; static struct kmem_cache *mnt_cache __ro_after_init; +struct vfsmount *knullfs __ro_after_init; /* private nullfs instance */ static DECLARE_RWSEM(namespace_sem); static HLIST_HEAD(unmounted); /* protected by namespace_sem */ static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */ @@ -6335,7 +6336,7 @@ static void __init init_mount_tree(void) * * (1) nullfs with mount id 1 * (2) mutable rootfs with mount id 2 - * (3) private nullfs for kthreads (SB_KERNMOUNT) + * (3) private nullfs for kthreads (SB_KERNMOUNT), kept in knullfs * * with (2) mounted on top of (1). The init_task's root and pwd * are pointed at (3) so all kthreads start isolated in nullfs. @@ -6370,11 +6371,11 @@ static void __init init_mount_tree(void) init_mnt_ns.nr_mounts++; } - nullfs_mnt = kern_mount(&nullfs_fs_type); - if (IS_ERR(nullfs_mnt)) + knullfs = kern_mount(&nullfs_fs_type); + if (IS_ERR(knullfs)) panic("VFS: Failed to create private nullfs instance"); - root.mnt = nullfs_mnt; - root.dentry = nullfs_mnt->mnt_root; + root.mnt = knullfs; + root.dentry = knullfs->mnt_root; init_task.nsproxy->mnt_ns = &init_mnt_ns; get_mnt_ns(&init_mnt_ns);