nfs: switch to ->iterate_shared()

aside of the usual care about seeding dcache from readdir, we need
to be careful about the pagecache evictions here.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/nfs/dir.c

@@ -57,7 +57,7 @@ static void nfs_readdir_clear_array(struct page*);
 const struct file_operations nfs_dir_operations = {
 	.llseek		= nfs_llseek_dir,
 	.read		= generic_read_dir,
-	.iterate	= nfs_readdir,
+	.iterate_shared	= nfs_readdir,
 	.open		= nfs_opendir,
 	.release	= nfs_closedir,
 	.fsync		= nfs_fsync_dir,
@@ -145,6 +145,7 @@ struct nfs_cache_array_entry {
 };
 
 struct nfs_cache_array {
+	atomic_t refcount;
 	int size;
 	int eof_index;
 	u64 last_cookie;
@@ -200,11 +201,20 @@ void nfs_readdir_clear_array(struct page *page)
 	int i;
 
 	array = kmap_atomic(page);
+	if (atomic_dec_and_test(&array->refcount))
 		for (i = 0; i < array->size; i++)
 			kfree(array->array[i].string.name);
 	kunmap_atomic(array);
 }
 
+static bool grab_page(struct page *page)
+{
+	struct nfs_cache_array *array = kmap_atomic(page);
+	bool res = atomic_inc_not_zero(&array->refcount);
+	kunmap_atomic(array);
+	return res;
+}
+
 /*
  * the caller is responsible for freeing qstr.name
  * when called by nfs_readdir_add_to_array, the strings will be freed in
@@ -470,6 +480,7 @@ static
 void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
 {
 	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);
@@ -489,7 +500,13 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
 	filename.hash = full_name_hash(filename.name, filename.len);
 
 	dentry = d_lookup(parent, &filename);
-	if (dentry != NULL) {
+again:
+	if (!dentry) {
+		dentry = d_alloc_parallel(parent, &filename, &wq);
+		if (IS_ERR(dentry))
+			return;
+	}
+	if (!d_in_lookup(dentry)) {
 		/* Is there a mountpoint here? If so, just exit */
 		if (!nfs_fsid_equal(&NFS_SB(dentry->d_sb)->fsid,
 					&entry->fattr->fsid))
@@ -503,26 +520,21 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
 		} else {
 			d_invalidate(dentry);
 			dput(dentry);
+			dentry = NULL;
+			goto again;
 		}
 	}
 
-	dentry = d_alloc(parent, &filename);
-	if (dentry == NULL)
-		return;
-
 	inode = nfs_fhget(dentry->d_sb, entry->fh, entry->fattr, entry->label);
-	if (IS_ERR(inode))
-		goto out;
-
 	alias = d_splice_alias(inode, dentry);
+	d_lookup_done(dentry);
+	if (alias) {
 		if (IS_ERR(alias))
 			goto out;
-	else if (alias) {
-		nfs_set_verifier(alias, nfs_save_change_attribute(dir));
-		dput(alias);
-	} else
+		dput(dentry);
+		dentry = alias;
+	}
 	nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
-
 out:
 	dput(dentry);
 }
@@ -643,6 +655,7 @@ int nfs_readdir_xdr_to_array(nfs_readdir_descriptor_t *desc, struct page *page,
 		goto out_label_free;
 	}
 	memset(array, 0, sizeof(struct nfs_cache_array));
+	atomic_set(&array->refcount, 1);
 	array->eof_index = -1;
 
 	status = nfs_readdir_alloc_pages(pages, array_size);
@@ -705,7 +718,6 @@ int nfs_readdir_filler(nfs_readdir_descriptor_t *desc, struct page* page)
 static
 void cache_page_release(nfs_readdir_descriptor_t *desc)
 {
-	if (!desc->page->mapping)
 	nfs_readdir_clear_array(desc->page);
 	put_page(desc->page);
 	desc->page = NULL;
@@ -714,8 +726,16 @@ void cache_page_release(nfs_readdir_descriptor_t *desc)
 static
 struct page *get_cache_page(nfs_readdir_descriptor_t *desc)
 {
-	return read_cache_page(file_inode(desc->file)->i_mapping,
+	struct page *page;
+
+	for (;;) {
+		page = read_cache_page(file_inode(desc->file)->i_mapping,
 			desc->page_index, (filler_t *)nfs_readdir_filler, desc);
+		if (IS_ERR(page) || grab_page(page))
+			break;
+		put_page(page);
+	}
+	return page;
 }
 
 /*
@@ -934,13 +954,11 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 
 static loff_t nfs_llseek_dir(struct file *filp, loff_t offset, int whence)
 {
-	struct inode *inode = file_inode(filp);
 	struct nfs_open_dir_context *dir_ctx = filp->private_data;
 
 	dfprintk(FILE, "NFS: llseek dir(%pD2, %lld, %d)\n",
 			filp, offset, whence);
 
-	inode_lock(inode);
 	switch (whence) {
 		case 1:
 			offset += filp->f_pos;
@@ -948,16 +966,13 @@ static loff_t nfs_llseek_dir(struct file *filp, loff_t offset, int whence)
 			if (offset >= 0)
 				break;
 		default:
-			offset = -EINVAL;
-			goto out;
+			return -EINVAL;
 	}
 	if (offset != filp->f_pos) {
 		filp->f_pos = offset;
 		dir_ctx->dir_cookie = 0;
 		dir_ctx->duped = 0;
 	}
-out:
-	inode_unlock(inode);
 	return offset;
 }