btrfs: scrub: skip initial RST lookup errors

Performing the initial extent sector read on a RAID stripe-tree backed
filesystem with pre-allocated extents will cause the RAID stripe-tree
lookup code to return ENODATA, as pre-allocated extents do not have any
on-disk bytes and thus no RAID stripe-tree entries.

But the current scrub read code marks these extents as errors, because
the lookup fails.

If btrfs_map_block() returns -ENODATA, it means that the call to
btrfs_get_raid_extent_offset() returned -ENODATA, because there is no
entry for the corresponding range in the RAID stripe-tree. But as this
range is in the extent tree it means we've hit a pre-allocated extent. In
this case, don't mark the sector in the stripe's error bitmaps as faulty
and carry on to the next.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index e141132b5c8d..52e09f307462 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -1704,8 +1704,18 @@ static void scrub_submit_extent_sector_read(struct scrub_ctx *sctx,
 					      &stripe_len, &bioc, &io_stripe, &mirror);
 			btrfs_put_bioc(bioc);
 			if (err < 0) {
-				set_bit(i, &stripe->io_error_bitmap);
-				set_bit(i, &stripe->error_bitmap);
+				if (err != -ENODATA) {
+					/*
+					 * Earlier btrfs_get_raid_extent_offset()
+					 * returned -ENODATA, which means there's
+					 * no entry for the corresponding range
+					 * in the stripe tree.  But if it's in
+					 * the extent tree, then it's a preallocated
+					 * extent and not an error.
+					 */
+					set_bit(i, &stripe->io_error_bitmap);
+					set_bit(i, &stripe->error_bitmap);
+				}
 				continue;
 			}