NFSv4: Avoid unnecessary scans of filesystems for expired delegations

The amount of looping through the list of delegations is occasionally
leading to soft lockups.  If the state manager was asked to reap the
expired delegations, it should scan only those filesystems that hold
delegations that need to be reaped.

Fixes: 7f156ef0bf ("NFSv4: Clean up nfs_delegation_reap_expired()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/delegation.c

@@ -1284,6 +1284,7 @@ static void nfs_mark_test_expired_delegation(struct nfs_server *server,
 		return;
 	clear_bit(NFS_DELEGATION_NEED_RECLAIM, &delegation->flags);
 	set_bit(NFS_DELEGATION_TEST_EXPIRED, &delegation->flags);
+	set_bit(NFS4SERV_DELEGATION_EXPIRED, &server->delegation_flags);
 	set_bit(NFS4CLNT_DELEGATION_EXPIRED, &server->nfs_client->cl_state);
 }
 
@@ -1362,6 +1363,9 @@ static int nfs_server_reap_expired_delegations(struct nfs_server *server,
 	nfs4_stateid stateid;
 	unsigned long gen = ++server->delegation_gen;
 
+	if (!test_and_clear_bit(NFS4SERV_DELEGATION_EXPIRED,
+				&server->delegation_flags))
+		return 0;
 restart:
 	rcu_read_lock();
 	list_for_each_entry_rcu(delegation, &server->delegations, super_list) {
@@ -1391,6 +1395,9 @@ restart:
 			goto restart;
 		}
 		nfs_inode_mark_test_expired_delegation(server,inode);
+		set_bit(NFS4SERV_DELEGATION_EXPIRED, &server->delegation_flags);
+		set_bit(NFS4CLNT_DELEGATION_EXPIRED,
+			&server->nfs_client->cl_state);
 		iput(inode);
 		return -EAGAIN;
 	}

include/linux/nfs_fs_sb.h

@@ -252,6 +252,7 @@ struct nfs_server {
 
 	unsigned long		delegation_flags;
 #define NFS4SERV_DELEGRETURN		(1)
+#define NFS4SERV_DELEGATION_EXPIRED	(2)
 	unsigned long		delegation_gen;
 	unsigned long		mig_gen;
 	unsigned long		mig_status;