NFSv4: Fix races between open and delegreturn

If the server returns the same delegation in an open that we just used
in a delegreturn, we need to ensure we don't apply that stateid if
the delegreturn has freed it on the server.
To do so, we ensure that we do not free the storage for the delegation
until either it is replaced by a new one, or we throw the inode out of
cache.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/delegation.c

@@ -229,7 +229,6 @@ static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *
 				delegation->cred,
 				&delegation->stateid,
 				issync);
-	nfs_free_delegation(delegation);
 	return res;
 }
 
@@ -302,7 +301,6 @@ nfs_detach_delegation_locked(struct nfs_inode *nfsi,
 		spin_unlock(&delegation->lock);
 		return NULL;
 	}
-	set_bit(NFS_DELEGATION_RETURNING, &delegation->flags);
 	list_del_rcu(&delegation->super_list);
 	delegation->inode = NULL;
 	rcu_assign_pointer(nfsi->delegation, NULL);
@@ -329,10 +327,12 @@ nfs_inode_detach_delegation(struct inode *inode)
 	struct nfs_server *server = NFS_SERVER(inode);
 	struct nfs_delegation *delegation;
 
-	delegation = nfs_start_delegation_return(nfsi);
-	if (delegation == NULL)
-		return NULL;
-	return nfs_detach_delegation(nfsi, delegation, server);
+	rcu_read_lock();
+	delegation = rcu_dereference(nfsi->delegation);
+	if (delegation != NULL)
+		delegation = nfs_detach_delegation(nfsi, delegation, server);
+	rcu_read_unlock();
+	return delegation;
 }
 
 static void
@@ -384,7 +384,8 @@ int nfs_inode_set_delegation(struct inode *inode, const struct cred *cred,
 	spin_lock(&clp->cl_lock);
 	old_delegation = rcu_dereference_protected(nfsi->delegation,
 					lockdep_is_held(&clp->cl_lock));
-	if (old_delegation != NULL) {
+	if (old_delegation == NULL)
+		goto add_new;
 	/* Is this an update of the existing delegation? */
 	if (nfs4_stateid_match_other(&old_delegation->stateid,
 				&delegation->stateid)) {
@@ -394,6 +395,7 @@ int nfs_inode_set_delegation(struct inode *inode, const struct cred *cred,
 		spin_unlock(&old_delegation->lock);
 		goto out;
 	}
+	if (!test_bit(NFS_DELEGATION_REVOKED, &old_delegation->flags)) {
 		/*
 		 * Deal with broken servers that hand out two
 		 * delegations for the same file.
@@ -412,11 +414,11 @@ int nfs_inode_set_delegation(struct inode *inode, const struct cred *cred,
 		if (test_and_set_bit(NFS_DELEGATION_RETURNING,
 					&old_delegation->flags))
 			goto out;
-		freeme = nfs_detach_delegation_locked(nfsi,
-				old_delegation, clp);
+	}
+	freeme = nfs_detach_delegation_locked(nfsi, old_delegation, clp);
 	if (freeme == NULL)
 		goto out;
-	}
+add_new:
 	list_add_tail_rcu(&delegation->super_list, &server->delegations);
 	rcu_assign_pointer(nfsi->delegation, delegation);
 	delegation = NULL;
@@ -431,8 +433,10 @@ int nfs_inode_set_delegation(struct inode *inode, const struct cred *cred,
 	spin_unlock(&clp->cl_lock);
 	if (delegation != NULL)
 		nfs_free_delegation(delegation);
-	if (freeme != NULL)
+	if (freeme != NULL) {
 		nfs_do_return_delegation(inode, freeme, 0);
+		nfs_free_delegation(freeme);
+	}
 	return status;
 }
 
@@ -442,7 +446,6 @@ int nfs_inode_set_delegation(struct inode *inode, const struct cred *cred,
 static int nfs_end_delegation_return(struct inode *inode, struct nfs_delegation *delegation, int issync)
 {
 	struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
-	struct nfs_inode *nfsi = NFS_I(inode);
 	int err = 0;
 
 	if (delegation == NULL)
@@ -464,8 +467,6 @@ static int nfs_end_delegation_return(struct inode *inode, struct nfs_delegation
 		nfs_abort_delegation_return(delegation, clp);
 		goto out;
 	}
-	if (!nfs_detach_delegation(nfsi, delegation, NFS_SERVER(inode)))
-		goto out;
 
 	err = nfs_do_return_delegation(inode, delegation, issync);
 out:
@@ -608,6 +609,7 @@ void nfs_inode_evict_delegation(struct inode *inode)
 	if (delegation != NULL) {
 		set_bit(NFS_DELEGATION_INODE_FREEING, &delegation->flags);
 		nfs_do_return_delegation(inode, delegation, 1);
+		nfs_free_delegation(delegation);
 	}
 }
 
@@ -763,10 +765,9 @@ static void nfs_mark_delegation_revoked(struct nfs_server *server,
 {
 	set_bit(NFS_DELEGATION_REVOKED, &delegation->flags);
 	delegation->stateid.type = NFS4_INVALID_STATEID_TYPE;
-	nfs_mark_return_delegation(server, delegation);
 }
 
-static bool nfs_revoke_delegation(struct inode *inode,
+static void nfs_revoke_delegation(struct inode *inode,
 		const nfs4_stateid *stateid)
 {
 	struct nfs_delegation *delegation;
@@ -799,19 +800,12 @@ static bool nfs_revoke_delegation(struct inode *inode,
 	rcu_read_unlock();
 	if (ret)
 		nfs_inode_find_state_and_recover(inode, stateid);
-	return ret;
 }
 
 void nfs_remove_bad_delegation(struct inode *inode,
 		const nfs4_stateid *stateid)
 {
-	struct nfs_delegation *delegation;
-
-	if (!nfs_revoke_delegation(inode, stateid))
-		return;
-	delegation = nfs_inode_detach_delegation(inode);
-	if (delegation)
-		nfs_free_delegation(delegation);
+	nfs_revoke_delegation(inode, stateid);
 }
 EXPORT_SYMBOL_GPL(nfs_remove_bad_delegation);
 
@@ -839,7 +833,7 @@ void nfs_delegation_mark_returned(struct inode *inode,
 			delegation->stateid.seqid = stateid->seqid;
 	}
 
-	set_bit(NFS_DELEGATION_REVOKED, &delegation->flags);
+	nfs_mark_delegation_revoked(NFS_SERVER(inode), delegation);
 
 out_clear_returning:
 	clear_bit(NFS_DELEGATION_RETURNING, &delegation->flags);