NFS: Fix up directory verifier races

In order to avoid having our dentry revalidation race with an update
of the directory on the server, we need to store the verifier before
the RPC calls to LOOKUP and READDIR.
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/dir.c

@@ -155,6 +155,7 @@ typedef struct {
 	loff_t		current_index;
 	decode_dirent_t	decode;
 
+	unsigned long	dir_verifier;
 	unsigned long	timestamp;
 	unsigned long	gencount;
 	unsigned int	cache_entry_index;
@@ -353,6 +354,7 @@ int nfs_readdir_xdr_filler(struct page **pages, nfs_readdir_descriptor_t *desc,
  again:
 	timestamp = jiffies;
 	gencount = nfs_inc_attr_generation_counter();
+	desc->dir_verifier = nfs_save_change_attribute(inode);
 	error = NFS_PROTO(inode)->readdir(file_dentry(file), cred, entry->cookie, pages,
 					  NFS_SERVER(inode)->dtsize, desc->plus);
 	if (error < 0) {
@@ -455,13 +457,13 @@ void nfs_force_use_readdirplus(struct inode *dir)
 }
 
 static
-void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
+void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry,
+		unsigned long dir_verifier)
 {
 	struct qstr filename = QSTR_INIT(entry->name, entry->len);
 	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
 	struct dentry *dentry;
 	struct dentry *alias;
-	struct inode *dir = d_inode(parent);
 	struct inode *inode;
 	int status;
 
@@ -500,7 +502,7 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
 		if (nfs_same_file(dentry, entry)) {
 			if (!entry->fh->size)
 				goto out;
-			nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
+			nfs_set_verifier(dentry, dir_verifier);
 			status = nfs_refresh_inode(d_inode(dentry), entry->fattr);
 			if (!status)
 				nfs_setsecurity(d_inode(dentry), entry->fattr, entry->label);
@@ -526,7 +528,7 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
 		dput(dentry);
 		dentry = alias;
 	}
-	nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
+	nfs_set_verifier(dentry, dir_verifier);
 out:
 	dput(dentry);
 }
@@ -564,7 +566,8 @@ int nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct nfs_entry *en
 		count++;
 
 		if (desc->plus)
-			nfs_prime_dcache(file_dentry(desc->file), entry);
+			nfs_prime_dcache(file_dentry(desc->file), entry,
+					desc->dir_verifier);
 
 		status = nfs_readdir_add_to_array(entry, page);
 		if (status != 0)
@@ -1159,6 +1162,7 @@ nfs_lookup_revalidate_dentry(struct inode *dir, struct dentry *dentry,
 	struct nfs_fh *fhandle;
 	struct nfs_fattr *fattr;
 	struct nfs4_label *label;
+	unsigned long dir_verifier;
 	int ret;
 
 	ret = -ENOMEM;
@@ -1168,6 +1172,7 @@ nfs_lookup_revalidate_dentry(struct inode *dir, struct dentry *dentry,
 	if (fhandle == NULL || fattr == NULL || IS_ERR(label))
 		goto out;
 
+	dir_verifier = nfs_save_change_attribute(dir);
 	ret = NFS_PROTO(dir)->lookup(dir, dentry, fhandle, fattr, label);
 	if (ret < 0) {
 		switch (ret) {
@@ -1188,7 +1193,7 @@ nfs_lookup_revalidate_dentry(struct inode *dir, struct dentry *dentry,
 		goto out;
 
 	nfs_setsecurity(inode, fattr, label);
-	nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
+	nfs_set_verifier(dentry, dir_verifier);
 
 	/* set a readdirplus hint that we had a cache miss */
 	nfs_force_use_readdirplus(dir);
@@ -1415,6 +1420,7 @@ struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, unsigned in
 	struct nfs_fh *fhandle = NULL;
 	struct nfs_fattr *fattr = NULL;
 	struct nfs4_label *label = NULL;
+	unsigned long dir_verifier;
 	int error;
 
 	dfprintk(VFS, "NFS: lookup(%pd2)\n", dentry);
@@ -1440,6 +1446,7 @@ struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, unsigned in
 	if (IS_ERR(label))
 		goto out;
 
+	dir_verifier = nfs_save_change_attribute(dir);
 	trace_nfs_lookup_enter(dir, dentry, flags);
 	error = NFS_PROTO(dir)->lookup(dir, dentry, fhandle, fattr, label);
 	if (error == -ENOENT)
@@ -1463,7 +1470,7 @@ struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, unsigned in
 			goto out_label;
 		dentry = res;
 	}
-	nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
+	nfs_set_verifier(dentry, dir_verifier);
 out_label:
 	trace_nfs_lookup_exit(dir, dentry, flags, error);
 	nfs4_label_free(label);