btrfs: allocate btrfs_ioctl_defrag_range_args on stack

Instead of using kmalloc() to allocate btrfs_ioctl_defrag_range_args,
allocate btrfs_ioctl_defrag_range_args on stack, the size is reasonably
small and ioctls are called in process context.

sizeof(btrfs_ioctl_defrag_range_args) = 48
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ioctl.c

@@ -3096,7 +3096,7 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp)
 {
 	struct inode *inode = file_inode(file);
 	struct btrfs_root *root = BTRFS_I(inode)->root;
-	struct btrfs_ioctl_defrag_range_args *range;
+	struct btrfs_ioctl_defrag_range_args range = {0};
 	int ret;
 
 	ret = mnt_want_write_file(file);
@@ -3134,33 +3134,24 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp)
 			goto out;
 		}
 
-		range = kzalloc(sizeof(*range), GFP_KERNEL);
-		if (!range) {
-			ret = -ENOMEM;
-			goto out;
-		}
-
 		if (argp) {
-			if (copy_from_user(range, argp,
-					   sizeof(*range))) {
+			if (copy_from_user(&range, argp, sizeof(range))) {
 				ret = -EFAULT;
-				kfree(range);
 				goto out;
 			}
 			/* compression requires us to start the IO */
-			if ((range->flags & BTRFS_DEFRAG_RANGE_COMPRESS)) {
-				range->flags |= BTRFS_DEFRAG_RANGE_START_IO;
-				range->extent_thresh = (u32)-1;
+			if ((range.flags & BTRFS_DEFRAG_RANGE_COMPRESS)) {
+				range.flags |= BTRFS_DEFRAG_RANGE_START_IO;
+				range.extent_thresh = (u32)-1;
 			}
 		} else {
 			/* the rest are all set to zero by kzalloc */
-			range->len = (u64)-1;
+			range.len = (u64)-1;
 		}
 		ret = btrfs_defrag_file(file_inode(file), file,
-					range, BTRFS_OLDEST_GENERATION, 0);
+					&range, BTRFS_OLDEST_GENERATION, 0);
 		if (ret > 0)
 			ret = 0;
-		kfree(range);
 		break;
 	default:
 		ret = -EINVAL;