nfsd4: don't do lookup within readdir in recovery code

The main nfsd code was recently modified to no longer do lookups from
withing the readdir callback, to avoid locking problems on certain
filesystems.

This (rather hacky, and overdue for replacement) NFSv4 recovery code has
the same problem.  Fix it to build up a list of names (instead of
dentries) and do the lookups afterwards.

Reported symptoms were a deadlock in the xfs code (called from
nfsd4_recdir_load), with /var/lib/nfs on xfs.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Reported-by: David Warren <warren@atmos.washington.edu>

fs/nfsd/nfs4recover.c

@@ -182,36 +182,26 @@ out_unlock:
 
 typedef int (recdir_func)(struct dentry *, struct dentry *);
 
-struct dentry_list {
-	struct dentry *dentry;
+struct name_list {
+	char name[HEXDIR_LEN];
 	struct list_head list;
 };
 
-struct dentry_list_arg {
-	struct list_head dentries;
-	struct dentry *parent;
-};
-
 static int
-nfsd4_build_dentrylist(void *arg, const char *name, int namlen,
+nfsd4_build_namelist(void *arg, const char *name, int namlen,
 		loff_t offset, u64 ino, unsigned int d_type)
 {
-	struct dentry_list_arg *dla = arg;
-	struct list_head *dentries = &dla->dentries;
-	struct dentry *parent = dla->parent;
-	struct dentry *dentry;
-	struct dentry_list *child;
+	struct list_head *names = arg;
+	struct name_list *entry;
 
-	if (name && isdotent(name, namlen))
+	if (namlen != HEXDIR_LEN - 1)
 		return 0;
-	dentry = lookup_one_len(name, parent, namlen);
-	if (IS_ERR(dentry))
-		return PTR_ERR(dentry);
-	child = kmalloc(sizeof(*child), GFP_KERNEL);
-	if (child == NULL)
+	entry = kmalloc(sizeof(struct name_list), GFP_KERNEL);
+	if (entry == NULL)
 		return -ENOMEM;
-	child->dentry = dentry;
-	list_add(&child->list, dentries);
+	memcpy(entry->name, name, HEXDIR_LEN - 1);
+	entry->name[HEXDIR_LEN - 1] = '\0';
+	list_add(&entry->list, names);
 	return 0;
 }
 
@@ -220,11 +210,9 @@ nfsd4_list_rec_dir(struct dentry *dir, recdir_func *f)
 {
 	const struct cred *original_cred;
 	struct file *filp;
-	struct dentry_list_arg dla = {
-		.parent = dir,
-	};
-	struct list_head *dentries = &dla.dentries;
-	struct dentry_list *child;
+	LIST_HEAD(names);
+	struct name_list *entry;
+	struct dentry *dentry;
 	int status;
 
 	if (!rec_dir_init)
@@ -233,31 +221,34 @@ nfsd4_list_rec_dir(struct dentry *dir, recdir_func *f)
 	status = nfs4_save_creds(&original_cred);
 	if (status < 0)
 		return status;
-	INIT_LIST_HEAD(dentries);
 
 	filp = dentry_open(dget(dir), mntget(rec_dir.mnt), O_RDONLY,
 			   current_cred());
 	status = PTR_ERR(filp);
 	if (IS_ERR(filp))
 		goto out;
-	INIT_LIST_HEAD(dentries);
-	status = vfs_readdir(filp, nfsd4_build_dentrylist, &dla);
+	status = vfs_readdir(filp, nfsd4_build_namelist, &names);
 	fput(filp);
-	while (!list_empty(dentries)) {
-		child = list_entry(dentries->next, struct dentry_list, list);
-		status = f(dir, child->dentry);
+	while (!list_empty(&names)) {
+		entry = list_entry(names.next, struct name_list, list);
+
+		dentry = lookup_one_len(entry->name, dir, HEXDIR_LEN-1);
+		if (IS_ERR(dentry)) {
+			status = PTR_ERR(dentry);
+			goto out;
+		}
+		status = f(dir, dentry);
+		dput(dentry);
 		if (status)
 			goto out;
-		list_del(&child->list);
-		dput(child->dentry);
-		kfree(child);
+		list_del(&entry->list);
+		kfree(entry);
 	}
 out:
-	while (!list_empty(dentries)) {
-		child = list_entry(dentries->next, struct dentry_list, list);
-		list_del(&child->list);
-		dput(child->dentry);
-		kfree(child);
+	while (!list_empty(&names)) {
+		entry = list_entry(names.next, struct name_list, list);
+		list_del(&entry->list);
+		kfree(entry);
 	}
 	nfs4_reset_creds(original_cred);
 	return status;