NFSv4: Fix races between open and dentry revalidation

We want to make sure that we revalidate the dentry if and only if
we've done an OPEN by filename.
In order to avoid races with remote changes to the directory on the
server, we want to save the verifier before calling OPEN. The exception
is if the server returned a delegation with our OPEN, as we then
know that the filename can't have changed on the server.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Reviewed-by: Benjamin Coddington <bcodding@gmail.com>
Tested-by: Benjamin Coddington <bcodding@gmail.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/nfs4file.c

@@ -87,7 +87,6 @@ nfs4_file_open(struct inode *inode, struct file *filp)
 	if (inode != d_inode(dentry))
 		goto out_drop;
 
-	nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
 	nfs_file_set_open_context(filp, ctx);
 	nfs_fscache_open_file(inode, filp);
 	err = 0;

fs/nfs/nfs4proc.c

@@ -2974,10 +2974,13 @@ static int _nfs4_open_and_get_state(struct nfs4_opendata *opendata,
 	struct dentry *dentry;
 	struct nfs4_state *state;
 	fmode_t acc_mode = _nfs4_ctx_to_accessmode(ctx);
+	struct inode *dir = d_inode(opendata->dir);
+	unsigned long dir_verifier;
 	unsigned int seq;
 	int ret;
 
 	seq = raw_seqcount_begin(&sp->so_reclaim_seqcount);
+	dir_verifier = nfs_save_change_attribute(dir);
 
 	ret = _nfs4_proc_open(opendata, ctx);
 	if (ret != 0)
@@ -3005,8 +3008,19 @@ static int _nfs4_open_and_get_state(struct nfs4_opendata *opendata,
 			dput(ctx->dentry);
 			ctx->dentry = dentry = alias;
 		}
-		nfs_set_verifier(dentry,
-				nfs_save_change_attribute(d_inode(opendata->dir)));
+	}
+
+	switch(opendata->o_arg.claim) {
+	default:
+		break;
+	case NFS4_OPEN_CLAIM_NULL:
+	case NFS4_OPEN_CLAIM_DELEGATE_CUR:
+	case NFS4_OPEN_CLAIM_DELEGATE_PREV:
+		if (!opendata->rpc_done)
+			break;
+		if (opendata->o_res.delegation_type != 0)
+			dir_verifier = nfs_save_change_attribute(dir);
+		nfs_set_verifier(dentry, dir_verifier);
 	}
 
 	/* Parse layoutget results before we check for access */