Btrfs: Properly cast before shifting

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 51466dc..5fa4504 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -764,7 +764,7 @@ static int prepare_pages(struct btrfs_root *root, struct file *file,
        }
        if (start_pos < inode->i_size) {
                u64 last_pos;
-               last_pos = (index + num_pages) << PAGE_CACHE_SHIFT;
+               last_pos = ((u64)index + num_pages) << PAGE_CACHE_SHIFT;
                lock_extent(&BTRFS_I(inode)->io_tree,
                            start_pos, last_pos - 1, GFP_NOFS);
                clear_extent_bits(&BTRFS_I(inode)->io_tree, start_pos,