NFS: Fix spurious readdir cookie loop messages

If the directory contents change, then we have to accept that the
file->f_pos value may shrink if we do a 'search-by-cookie'. In that
case, we should turn off the loop detection and let the NFS client
try to recover.

The patch also fixes a second loop detection bug by ensuring
that after turning on the ctx->duped flag, we read at least one new
cookie into ctx->dir_cookie before attempting to match with
ctx->dup_cookie.
Reported-by: Petr Vandrovec <petr@vandrovec.name>
Cc: stable@kernel.org [2.6.39+]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/dir.c

@@ -134,18 +134,19 @@ const struct inode_operations nfs4_dir_inode_operations = {
 
 #endif /* CONFIG_NFS_V4 */
 
-static struct nfs_open_dir_context *alloc_nfs_open_dir_context(struct rpc_cred *cred)
+static struct nfs_open_dir_context *alloc_nfs_open_dir_context(struct inode *dir, struct rpc_cred *cred)
 {
 	struct nfs_open_dir_context *ctx;
 	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 	if (ctx != NULL) {
 		ctx->duped = 0;
+		ctx->attr_gencount = NFS_I(dir)->attr_gencount;
 		ctx->dir_cookie = 0;
 		ctx->dup_cookie = 0;
 		ctx->cred = get_rpccred(cred);
-	} else
-		ctx = ERR_PTR(-ENOMEM);
-	return ctx;
+		return ctx;
+	}
+	return  ERR_PTR(-ENOMEM);
 }
 
 static void put_nfs_open_dir_context(struct nfs_open_dir_context *ctx)
@@ -173,7 +174,7 @@ nfs_opendir(struct inode *inode, struct file *filp)
 	cred = rpc_lookup_cred();
 	if (IS_ERR(cred))
 		return PTR_ERR(cred);
-	ctx = alloc_nfs_open_dir_context(cred);
+	ctx = alloc_nfs_open_dir_context(inode, cred);
 	if (IS_ERR(ctx)) {
 		res = PTR_ERR(ctx);
 		goto out;
@@ -323,7 +324,6 @@ int nfs_readdir_search_for_pos(struct nfs_cache_array *array, nfs_readdir_descri
 {
 	loff_t diff = desc->file->f_pos - desc->current_index;
 	unsigned int index;
-	struct nfs_open_dir_context *ctx = desc->file->private_data;
 
 	if (diff < 0)
 		goto out_eof;
@@ -336,7 +336,6 @@ int nfs_readdir_search_for_pos(struct nfs_cache_array *array, nfs_readdir_descri
 	index = (unsigned int)diff;
 	*desc->dir_cookie = array->array[index].cookie;
 	desc->cache_entry_index = index;
-	ctx->duped = 0;
 	return 0;
 out_eof:
 	desc->eof = 1;
@@ -349,14 +348,33 @@ int nfs_readdir_search_for_cookie(struct nfs_cache_array *array, nfs_readdir_des
 	int i;
 	loff_t new_pos;
 	int status = -EAGAIN;
-	struct nfs_open_dir_context *ctx = desc->file->private_data;
 
 	for (i = 0; i < array->size; i++) {
 		if (array->array[i].cookie == *desc->dir_cookie) {
+			struct nfs_inode *nfsi = NFS_I(desc->file->f_path.dentry->d_inode);
+			struct nfs_open_dir_context *ctx = desc->file->private_data;
+
 			new_pos = desc->current_index + i;
-			if (new_pos < desc->file->f_pos) {
+			if (ctx->attr_gencount != nfsi->attr_gencount
+			    || (nfsi->cache_validity & (NFS_INO_INVALID_ATTR|NFS_INO_INVALID_DATA))) {
+				ctx->duped = 0;
+				ctx->attr_gencount = nfsi->attr_gencount;
+			} else if (new_pos < desc->file->f_pos) {
+				if (ctx->duped > 0
+				    && ctx->dup_cookie == *desc->dir_cookie) {
+					if (printk_ratelimit()) {
+						pr_notice("NFS: directory %s/%s contains a readdir loop."
+								"Please contact your server vendor.  "
+								"Offending cookie: %llu\n",
+								desc->file->f_dentry->d_parent->d_name.name,
+								desc->file->f_dentry->d_name.name,
+								*desc->dir_cookie);
+					}
+					status = -ELOOP;
+					goto out;
+				}
 				ctx->dup_cookie = *desc->dir_cookie;
-				ctx->duped = 1;
+				ctx->duped = -1;
 			}
 			desc->file->f_pos = new_pos;
 			desc->cache_entry_index = i;
@@ -368,6 +386,7 @@ int nfs_readdir_search_for_cookie(struct nfs_cache_array *array, nfs_readdir_des
 		if (*desc->dir_cookie == array->last_cookie)
 			desc->eof = 1;
 	}
+out:
 	return status;
 }
 
@@ -740,19 +759,6 @@ int nfs_do_filldir(nfs_readdir_descriptor_t *desc, void *dirent,
 	struct nfs_cache_array *array = NULL;
 	struct nfs_open_dir_context *ctx = file->private_data;
 
-	if (ctx->duped != 0 && ctx->dup_cookie == *desc->dir_cookie) {
-		if (printk_ratelimit()) {
-			pr_notice("NFS: directory %s/%s contains a readdir loop.  "
-				"Please contact your server vendor.  "
-				"Offending cookie: %llu\n",
-				file->f_dentry->d_parent->d_name.name,
-				file->f_dentry->d_name.name,
-				*desc->dir_cookie);
-		}
-		res = -ELOOP;
-		goto out;
-	}
-
 	array = nfs_readdir_get_array(desc->page);
 	if (IS_ERR(array)) {
 		res = PTR_ERR(array);
@@ -774,6 +780,8 @@ int nfs_do_filldir(nfs_readdir_descriptor_t *desc, void *dirent,
 			*desc->dir_cookie = array->array[i+1].cookie;
 		else
 			*desc->dir_cookie = array->last_cookie;
+		if (ctx->duped != 0)
+			ctx->duped = 1;
 	}
 	if (array->eof_index >= 0)
 		desc->eof = 1;
@@ -805,6 +813,7 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc, void *dirent,
 	struct page	*page = NULL;
 	int		status;
 	struct inode *inode = desc->file->f_path.dentry->d_inode;
+	struct nfs_open_dir_context *ctx = desc->file->private_data;
 
 	dfprintk(DIRCACHE, "NFS: uncached_readdir() searching for cookie %Lu\n",
 			(unsigned long long)*desc->dir_cookie);
@@ -818,6 +827,7 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc, void *dirent,
 	desc->page_index = 0;
 	desc->last_cookie = *desc->dir_cookie;
 	desc->page = page;
+	ctx->duped = 0;
 
 	status = nfs_readdir_xdr_to_array(desc, page, inode);
 	if (status < 0)

include/linux/nfs_fs.h

@@ -99,9 +99,10 @@ struct nfs_open_context {
 
 struct nfs_open_dir_context {
 	struct rpc_cred *cred;
+	unsigned long attr_gencount;
 	__u64 dir_cookie;
 	__u64 dup_cookie;
-	int duped;
+	signed char duped;
 };
 
 /*