NFSv4: Fix an infinite looping problem with the nfs4_state_manager

Commit 76db6d9500caeaa774a3e32a997eba30bbdc176b (nfs41: add session setup
to the state manager) introduces an infinite loop possibility in the NFSv4
state manager. By first checking nfs4_has_session() before clearing the
NFS4CLNT_SESSION_SETUP flag, it allows for a situation where someone sets
that flag, but it never gets cleared, and so the state manager loops.

In fact commit c3fad1b1aaf850bf692642642ace7cd0d64af0a3 (nfs41: add session
reset to state manager) causes this to happen every time we get a network
partition error.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Tested-by: Daniel J Blueman <daniel.blueman@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nfs/nfs4state.c

@@ -1250,8 +1250,8 @@ static void nfs4_state_manager(struct nfs_client *clp)
 				continue;
 		}
 		/* Initialize or reset the session */
-		if (nfs4_has_session(clp) &&
-		   test_and_clear_bit(NFS4CLNT_SESSION_SETUP, &clp->cl_state)) {
+		if (test_and_clear_bit(NFS4CLNT_SESSION_SETUP, &clp->cl_state)
+		   && nfs4_has_session(clp)) {
 			if (clp->cl_cons_state == NFS_CS_SESSION_INITING)
 				status = nfs4_initialize_session(clp);
 			else