NFS: Initialise verifiers for visible dentries in _nfs4_open_and_get_state

Ensure that the verifiers are initialised before calling
d_splice_alias() in _nfs4_open_and_get_state().

Reported-by: Michael Stoler <michael.stoler@vastdata.com>
Fixes: cf5b405 ("NFSv4: Fix races between open and dentry revalidation")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Author: Trond Myklebust

fs/nfs/nfs4proc.c

@@ -3174,18 +3174,6 @@ static int _nfs4_open_and_get_state(struct nfs4_opendata *opendata,
 	if (opendata->o_res.rflags & NFS4_OPEN_RESULT_PRESERVE_UNLINKED)
 		set_bit(NFS_INO_PRESERVE_UNLINKED, &NFS_I(state->inode)->flags);
 
-	dentry = opendata->dentry;
-	if (d_really_is_negative(dentry)) {
-		struct dentry *alias;
-		d_drop(dentry);
-		alias = d_splice_alias(igrab(state->inode), dentry);
-		/* d_splice_alias() can't fail here - it's a non-directory */
-		if (alias) {
-			dput(ctx->dentry);
-			ctx->dentry = dentry = alias;
-		}
-	}
-
 	switch(opendata->o_arg.claim) {
 	default:
 		break;
@@ -3196,7 +3184,20 @@ static int _nfs4_open_and_get_state(struct nfs4_opendata *opendata,
 			break;
 		if (opendata->o_res.delegation.type != 0)
 			dir_verifier = nfs_save_change_attribute(dir);
-		nfs_set_verifier(dentry, dir_verifier);
+	}
+
+	dentry = opendata->dentry;
+	nfs_set_verifier(dentry, dir_verifier);
+	if (d_really_is_negative(dentry)) {
+		struct dentry *alias;
+		d_drop(dentry);
+		alias = d_splice_alias(igrab(state->inode), dentry);
+		/* d_splice_alias() can't fail here - it's a non-directory */
+		if (alias) {
+			dput(ctx->dentry);
+			nfs_set_verifier(alias, dir_verifier);
+			ctx->dentry = dentry = alias;
+		}
 	}
 
 	/* Parse layoutget results before we check for access */