Commit e30da2a2 authored by Al Viro's avatar Al Viro
Browse files

pivot_root(): reorder tree surgeries, collapse unhash_mnt() and put_mountpoint() 



attach new_mnt *before* detaching root_mnt; that way we don't need to keep hold
on the mountpoint and one more pair of unhash_mnt()/put_mountpoint() gets
folded together into umount_mnt().

Reviewed-by: default avatarChristian Brauner <brauner@kernel.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent ec3265a2

fs/namespace.c

+5 −6
Original line number Diff line number Diff line
@@ -4685,7 +4685,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, 
{

	struct path new, old, root;

	struct mount *new_mnt, *root_mnt, *old_mnt, *root_parent, *ex_parent;

	struct mountpoint *old_mp, *root_mp;

	struct mountpoint *old_mp;

	int error;



	if (!may_mount())
@@ -4748,20 +4748,19 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, 
		goto out4;

	lock_mount_hash();

	umount_mnt(new_mnt);

	root_mp = unhash_mnt(root_mnt);  /* we'll need its mountpoint */

	if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {

		new_mnt->mnt.mnt_flags |= MNT_LOCKED;

		root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;

	}

	/* mount old root on put_old */

	attach_mnt(root_mnt, old_mnt, old_mp);

	/* mount new_root on / */

	attach_mnt(new_mnt, root_parent, root_mp);

	attach_mnt(new_mnt, root_parent, root_mnt->mnt_mp);

	umount_mnt(root_mnt);

	mnt_add_count(root_parent, -1);

	/* mount old root on put_old */

	attach_mnt(root_mnt, old_mnt, old_mp);

	touch_mnt_namespace(current->nsproxy->mnt_ns);

	/* A moved mount should not expire automatically */

	list_del_init(&new_mnt->mnt_expire);

	put_mountpoint(root_mp);

	unlock_mount_hash();

	mnt_notify_add(root_mnt);

	mnt_notify_add(new_mnt);