NFS: Fix a soft lockup in the delegation recovery code

Fix a soft lockup when NFS client delegation recovery is attempted
but the inode is in the process of being freed. When the
igrab(inode) call fails, and we have to restart the recovery process,
we need to ensure that we won't attempt to recover the same delegation
again.

Fixes: 45870d69 ("NFSv4.1: Test delegation stateids when server...")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/delegation.c

@@ -229,6 +229,8 @@ static struct inode *nfs_delegation_grab_inode(struct nfs_delegation *delegation
 	spin_lock(&delegation->lock);
 	if (delegation->inode != NULL)
 		inode = igrab(delegation->inode);
+	if (!inode)
+		set_bit(NFS_DELEGATION_INODE_FREEING, &delegation->flags);
 	spin_unlock(&delegation->lock);
 	return inode;
 }
@@ -944,10 +946,11 @@ void nfs_delegation_reap_unclaimed(struct nfs_client *clp)
 	list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link) {
 		list_for_each_entry_rcu(delegation, &server->delegations,
 								super_list) {
-			if (test_bit(NFS_DELEGATION_RETURNING,
-						&delegation->flags))
-				continue;
-			if (test_bit(NFS_DELEGATION_NEED_RECLAIM,
+			if (test_bit(NFS_DELEGATION_INODE_FREEING,
+						&delegation->flags) ||
+			    test_bit(NFS_DELEGATION_RETURNING,
+						&delegation->flags) ||
+			    test_bit(NFS_DELEGATION_NEED_RECLAIM,
 						&delegation->flags) == 0)
 				continue;
 			if (!nfs_sb_active(server->super))
@@ -1053,10 +1056,11 @@ void nfs_reap_expired_delegations(struct nfs_client *clp)
 	list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link) {
 		list_for_each_entry_rcu(delegation, &server->delegations,
 								super_list) {
-			if (test_bit(NFS_DELEGATION_RETURNING,
-						&delegation->flags))
-				continue;
-			if (test_bit(NFS_DELEGATION_TEST_EXPIRED,
+			if (test_bit(NFS_DELEGATION_INODE_FREEING,
+						&delegation->flags) ||
+			    test_bit(NFS_DELEGATION_RETURNING,
+						&delegation->flags) ||
+			    test_bit(NFS_DELEGATION_TEST_EXPIRED,
 						&delegation->flags) == 0)
 				continue;
 			if (!nfs_sb_active(server->super))

fs/nfs/delegation.h

@@ -34,6 +34,7 @@ enum {
 	NFS_DELEGATION_RETURNING,
 	NFS_DELEGATION_REVOKED,
 	NFS_DELEGATION_TEST_EXPIRED,
+	NFS_DELEGATION_INODE_FREEING,
 };
 
 int nfs_inode_set_delegation(struct inode *inode, const struct cred *cred,