Btrfs: fix eof while discarding extents

We miscalculate the length of extents we're discarding, and it leads to
an eof of device.

Reported-by: Daniel Blueman <daniel@quora.org>
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a872b48be0ae15fd77eff56e2c529470ddde0b7f..759d02486d7ccb2dcb2ff1b1334396cc219880ca 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3833,6 +3833,7 @@ static int __btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
                int sub_stripes = 0;
                u64 stripes_per_dev = 0;
                u32 remaining_stripes = 0;
+               u32 last_stripe = 0;
 
                if (map->type &
                    (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10)) {
@@ -3846,6 +3847,8 @@ static int __btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
                                                      stripe_nr_orig,
                                                      factor,
                                                      &remaining_stripes);
+                       div_u64_rem(stripe_nr_end - 1, factor, &last_stripe);
+                       last_stripe *= sub_stripes;
                }
 
                for (i = 0; i < num_stripes; i++) {
@@ -3858,16 +3861,29 @@ static int __btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
                                         BTRFS_BLOCK_GROUP_RAID10)) {
                                bbio->stripes[i].length = stripes_per_dev *
                                                          map->stripe_len;
+
                                if (i / sub_stripes < remaining_stripes)
                                        bbio->stripes[i].length +=
                                                map->stripe_len;
+
+                               /*
+                                * Special for the first stripe and
+                                * the last stripe:
+                                *
+                                * |-------|...|-------|
+                                *     |----------|
+                                *    off     end_off
+                                */
                                if (i < sub_stripes)
                                        bbio->stripes[i].length -=
                                                stripe_offset;
-                               if ((i / sub_stripes + 1) %
-                                   sub_stripes == remaining_stripes)
+
+                               if (stripe_index >= last_stripe &&
+                                   stripe_index <= (last_stripe +
+                                                    sub_stripes - 1))
                                        bbio->stripes[i].length -=
                                                stripe_end_offset;
+
                                if (i == sub_stripes - 1)
                                        stripe_offset = 0;
                        } else