block: fix get_max_segment_size() overflow on 32bit arch

Commit 429120f 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 in case of zero physical address on 32bit arch. Fix the issue by returning queue_max_segment_size() directly when that happens. Fixes: 429120f ("block: fix splitting segments on boundary masks") Reported-by: Guenter Roeck <[email protected]> Tested-by: Guenter Roeck <[email protected]> Cc: Christoph Hellwig <[email protected]> Tested-by: Steven Rostedt (VMware) <[email protected]> Signed-off-by: Ming Lei <[email protected]> Signed-off-by: Jens Axboe <[email protected]>
niw · Jan 14, 2020 · 4a2f704 · 4a2f704
1 parent e17016f
commit 4a2f704
Showing 1 changed file with 7 additions and 2 deletions.
diff --git a/block/blk-merge.c b/block/blk-merge.c
@@ -164,8 +164,13 @@ static inline unsigned get_max_segment_size(const struct request_queue *q,
 	unsigned long mask = queue_segment_boundary(q);
 
 	offset = mask & (page_to_phys(start_page) + offset);
-	return min_t(unsigned long, mask - offset + 1,
-		     queue_max_segment_size(q));
+
+	/*
+	 * overflow may be triggered in case of zero page physical address
+	 * on 32bit arch, use queue's max segment size when that happens.
+	 */
+	return min_not_zero(mask - offset + 1,
+			(unsigned long)queue_max_segment_size(q));
 }
 
 /**