1 files changed, 27 insertions, 6 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index fd3f172e94e6..714adc4ac4c2 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3046,17 +3046,38 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
         }
 
         while (!end) {
-                off = extent_map_end(em);
-                if (off >= max)
-                        end = 1;
+                u64 offset_in_extent;
+
+                /* break if the extent we found is outside the range */
+                if (em->start >= max || extent_map_end(em) < off)
+                        break;
+
+                /*
+                 * get_extent may return an extent that starts before our
+                 * requested range.  We have to make sure the ranges
+                 * we return to fiemap always move forward and don't
+                 * overlap, so adjust the offsets here
+                 */
+                em_start = max(em->start, off);
 
-                em_start = em->start;
-                em_len = em->len;
+                /*
+                 * record the offset from the start of the extent
+                 * for adjusting the disk offset below
+                 */
+                offset_in_extent = em_start - em->start;
                 em_end = extent_map_end(em);
+                em_len = em_end - em_start;
                 emflags = em->flags;
                 disko = 0;
                 flags = 0;
 
+                /*
+                 * bump off for our next call to get_extent
+                 */
+                off = extent_map_end(em);
+                if (off >= max)
+                        end = 1;
+
                 if (em->block_start == EXTENT_MAP_LAST_BYTE) {
                         end = 1;
                         flags |= FIEMAP_EXTENT_LAST;
@@ -3067,7 +3088,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
                         flags |= (FIEMAP_EXTENT_DELALLOC |
                                   FIEMAP_EXTENT_UNKNOWN);
                 } else {
-                        disko = em->block_start;
+                        disko = em->block_start + offset_in_extent;
                 }
                 if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
                         flags |= FIEMAP_EXTENT_ENCODED;