block: hold ->invalidate_lock in blkdev_fallocate

When running ->fallocate(), blkdev_fallocate() should hold
mapping->invalidate_lock to prevent page cache from being
accessed, otherwise stale data may be read in page cache.

Without this patch, blktests block/009 fails sometimes. With
this patch, block/009 can pass always.

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Ming Lei <ming.lei@redhat.com>

fs/block_dev.c

@@ -1699,7 +1699,8 @@ static const struct address_space_operations def_blk_aops = {
 static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 			     loff_t len)
 {
-	struct block_device *bdev = I_BDEV(bdev_file_inode(file));
+	struct inode *inode = bdev_file_inode(file);
+	struct block_device *bdev = I_BDEV(inode);
 	loff_t end = start + len - 1;
 	loff_t isize;
 	int error;
@@ -1726,10 +1727,12 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 	if ((start | len) & (bdev_logical_block_size(bdev) - 1))
 		return -EINVAL;
 
+	filemap_invalidate_lock(inode->i_mapping);
+
 	/* Invalidate the page cache, including dirty pages. */
 	error = truncate_bdev_range(bdev, file->f_mode, start, end);
 	if (error)
-		return error;
+		goto fail;
 
 	switch (mode) {
 	case FALLOC_FL_ZERO_RANGE:
@@ -1746,17 +1749,18 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 					     GFP_KERNEL, 0);
 		break;
 	default:
-		return -EOPNOTSUPP;
+		error = -EOPNOTSUPP;
 	}
-	if (error)
-		return error;
-
 	/*
 	 * Invalidate the page cache again; if someone wandered in and dirtied
 	 * a page, we just discard it - userspace has no way of knowing whether
 	 * the write happened before or after discard completing...
 	 */
-	return truncate_bdev_range(bdev, file->f_mode, start, end);
+	if (!error)
+		error = truncate_bdev_range(bdev, file->f_mode, start, end);
+ fail:
+	filemap_invalidate_unlock(inode->i_mapping);
+	return error;
 }
 
 const struct file_operations def_blk_fops = {