NFS: nfs_delegation_find_inode_server must first reference the superblock

stable inclusion
from stable-5.10.9
commit b4689562fa95100caf31b2190bba84cb0e10770f
bugzilla: 47457

--------------------------------

commit 113aac6d upstream.

Before referencing the inode, we must ensure that the superblock can be
referenced. Otherwise, we can end up with iput() calling superblock
operations that are no longer valid or accessible.

Fixes: e39d8a18 ("NFSv4: Fix an Oops during delegation callbacks")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>