NFSv4.2: fix failure to unregister shrinker

We forgot to unregister the nfs4_xattr_large_entry_shrinker.

That leaves the global list of shrinkers corrupted after unload of the
nfs module, after which possibly unrelated code that calls
register_shrinker() or unregister_shrinker() gets a BUG() with
"supervisor write access in kernel mode".

And similarly for the nfs4_xattr_large_entry_lru.
Reported-by: Kris Karas <bugs-a17@moonlit-rail.com>
Tested-By: Kris Karas <bugs-a17@moonlit-rail.com>
Fixes: 95ad37f9 "NFSv4.2: add client side xattr caching."
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
CC: stable@vger.kernel.org
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/nfs42xattr.c

@@ -1047,8 +1047,10 @@ int __init nfs4_xattr_cache_init(void)
 
 void nfs4_xattr_cache_exit(void)
 {
+	unregister_shrinker(&nfs4_xattr_large_entry_shrinker);
 	unregister_shrinker(&nfs4_xattr_entry_shrinker);
 	unregister_shrinker(&nfs4_xattr_cache_shrinker);
+	list_lru_destroy(&nfs4_xattr_large_entry_lru);
 	list_lru_destroy(&nfs4_xattr_entry_lru);
 	list_lru_destroy(&nfs4_xattr_cache_lru);
 	kmem_cache_destroy(nfs4_xattr_cache_cachep);