[PATCH 4/6 v5] ext4: Correct large hole offset calcuation

[Allison Henderson <achender@linux.vnet.ibm.com>]

This bug was reported by Lukas Czerner while working on a
new patch to add discard support for loop devices using
punch hole.

The bug is happens because the data type for logical blocks is
not large enough to calculate the block offset for holes that are
very large.  This bug is resolved by casting the ext4_lblk_t
to an loff_t before calculating the byte offset of the block.

Reviewed-and-Tested-by: Lukas Czerner <lczerner@redhat.com>

Signed-off-by: Allison Henderson <achender@linux.vnet.ibm.com>
---
:100644 100644 0d7617d... b417e47... M	fs/ext4/extents.c
 fs/ext4/extents.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0d7617d..b417e47 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4179,8 +4179,8 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
 		EXT4_BLOCK_SIZE_BITS(sb);
 	last_block = (offset + length) >> EXT4_BLOCK_SIZE_BITS(sb);
 
-	first_block_offset = first_block << EXT4_BLOCK_SIZE_BITS(sb);
-	last_block_offset = last_block << EXT4_BLOCK_SIZE_BITS(sb);
+	first_block_offset = ((loff_t)first_block) << EXT4_BLOCK_SIZE_BITS(sb);
+	last_block_offset = ((loff_t)last_block) << EXT4_BLOCK_SIZE_BITS(sb);
 
 	first_page = (offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 	last_page = (offset + length) >> PAGE_CACHE_SHIFT;
-- 
1.7.1