[PATCH] block: fix get_max_segment_size() overflow on 32bit arch

[Ming Lei <ming.lei@redhat.com>]

Commit 429120f3df2d starts to take account of segment's start dma address
when computing max segment size, and data type of 'unsigned long'
is used to do that. However, the segment mask may be 0xffffffff, so
the figured out segment size may be overflowed because DMA address can
be 64bit on 32bit arch.

Fixes the issue by using 'unsigned long long' to compute max segment
size.

Fixes: 429120f3df2d ("block: fix splitting segments on boundary masks")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-merge.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 347782a24a35..b0fcc72594cb 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -159,12 +159,12 @@ static inline unsigned get_max_io_size(struct request_queue *q,
 
 static inline unsigned get_max_segment_size(const struct request_queue *q,
 					    struct page *start_page,
-					    unsigned long offset)
+					    unsigned long long offset)
 {
 	unsigned long mask = queue_segment_boundary(q);
 
 	offset = mask & (page_to_phys(start_page) + offset);
-	return min_t(unsigned long, mask - offset + 1,
+	return min_t(unsigned long long, mask - offset + 1,
 		     queue_max_segment_size(q));
 }
 
-- 
2.20.1