2 files changed, 24 insertions, 8 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 3dd846e801f..561313a7dac 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1030,17 +1030,27 @@ static void end_clone_request(struct request *clone, int error)
         dm_complete_request(clone, error);
 }
 
-static sector_t max_io_len(struct mapped_device *md,
-                           sector_t sector, struct dm_target *ti)
+/*
+ * Return maximum size of I/O possible at the supplied sector up to the current
+ * target boundary.
+ */
+static sector_t max_io_len_target_boundary(sector_t sector, struct dm_target *ti)
+{
+        sector_t target_offset = dm_target_offset(ti, sector);
+
+        return ti->len - target_offset;
+}
+
+static sector_t max_io_len(sector_t sector, struct dm_target *ti)
 {
-        sector_t offset = sector - ti->begin;
-        sector_t len = ti->len - offset;
+        sector_t len = max_io_len_target_boundary(sector, ti);
 
         /*
          * Does the target need to split even further ?
          */
         if (ti->split_io) {
                 sector_t boundary;
+                sector_t offset = dm_target_offset(ti, sector);
                 boundary = ((offset + ti->split_io) & ~(ti->split_io - 1))
                            - offset;
                 if (len > boundary)
@@ -1258,7 +1268,7 @@ static int __clone_and_map_discard(struct clone_info *ci)
         if (!ti->num_discard_requests)
                 return -EOPNOTSUPP;
 
-        max = max_io_len(ci->md, ci->sector, ti);
+        max = max_io_len(ci->sector, ti);
 
         if (ci->sector_count > max)
                 /*
@@ -1290,7 +1300,7 @@ static int __clone_and_map(struct clone_info *ci)
         if (!dm_target_is_valid(ti))
                 return -EIO;
 
-        max = max_io_len(ci->md, ci->sector, ti);
+        max = max_io_len(ci->sector, ti);
 
         if (ci->sector_count <= max) {
                 /*
@@ -1341,7 +1351,7 @@ static int __clone_and_map(struct clone_info *ci)
                                 if (!dm_target_is_valid(ti))
                                         return -EIO;
 
-                                max = max_io_len(ci->md, ci->sector, ti);
+                                max = max_io_len(ci->sector, ti);
                         }
 
                         len = min(remaining, max);
@@ -1428,7 +1438,7 @@ static int dm_merge_bvec(struct request_queue *q,
         /*
          * Find maximum amount of I/O that won't need splitting
          */
-        max_sectors = min(max_io_len(md, bvm->bi_sector, ti),
+        max_sectors = min(max_io_len(bvm->bi_sector, ti),
                           (sector_t) BIO_MAX_SECTORS);
         max_size = (max_sectors << SECTOR_SHIFT) - bvm->bi_size;
         if (max_size < 0)
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 751ce21dea7..2970022faa6 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -398,6 +398,12 @@ void *dm_vcalloc(unsigned long nmemb, unsigned long elem_size);
 #define dm_array_too_big(fixed, obj, num) \
         ((num) > (UINT_MAX - (fixed)) / (obj))
 
+/*
+ * Sector offset taken relative to the start of the target instead of
+ * relative to the start of the device.
+ */
+#define dm_target_offset(ti, sector) ((sector) - (ti)->begin)
+
 static inline sector_t to_sector(unsigned long n)
 {
         return (n >> SECTOR_SHIFT);