[PATCH] btrfs: Continue replace when set_block_ro failed

[Zhao Lei <zhaolei@xxxxxxxxxxxxxx>]

xfstests/011 failed in node with small_size filesystem.
Can be reproduced by following script:
  DEV_LIST="/dev/vdd /dev/vde"
  DEV_REPLACE="/dev/vdf"

  do_test()
  {
      local mkfs_opt="$1"
      local size="$2"

      dmesg -c >/dev/null
      umount $SCRATCH_MNT &>/dev/null

      echo  mkfs.btrfs -f $mkfs_opt "${DEV_LIST[*]}"
      mkfs.btrfs -f $mkfs_opt "${DEV_LIST[@]}" || return 1
      mount "${DEV_LIST[0]}" $SCRATCH_MNT

      echo -n "Writing big files"
      dd if=/dev/urandom of=$SCRATCH_MNT/t0 bs=1M count=1 >/dev/null 2>&1
      for ((i = 1; i <= size; i++)); do
          echo -n .
          /bin/cp $SCRATCH_MNT/t0 $SCRATCH_MNT/t$i || return 1
      done
      echo

      echo Start replace
      btrfs replace start -Bf "${DEV_LIST[0]}" "$DEV_REPLACE" $SCRATCH_MNT || {
          dmesg
          return 1
      }
      return 0
  }

  # Set size to value near fs size
  # for example, 1897 can trigger this bug in 2.6G device.
  #
  ./do_test "-d raid1 -m raid1" 1897

System will report replace fail with following warning in dmesg:

Reason:
 When big data writen to fs, the whole free space will be allocated
 for data chunk.
 And operation as scrub need to set_block_ro(), and when there is
 only one metadata chunk in system(or other metadata chunks
 are all full), the function will try to allocate a new chunk,
 and failed because no space in device.

Fix:
 When set_block_ro failed for metadata chunk, it is not a problem
 because scrub_lock forbids commit_trancaction.
 Let replace continue in this case is no problem.

Tested by above script, and xfstests/011, plus 100 times xfstests/070.

Signed-off-by: Zhao Lei <zhaolei@xxxxxxxxxxxxxx>
---
 fs/btrfs/scrub.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index a39f5d1..5a30753 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3532,6 +3532,7 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 	u64 length;
 	u64 chunk_offset;
 	int ret = 0;
+	int ro_set = 0;
 	int slot;
 	struct extent_buffer *l;
 	struct btrfs_key key;
@@ -3617,10 +3618,7 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 		scrub_pause_on(fs_info);
 		ret = btrfs_inc_block_group_ro(root, cache);
 		scrub_pause_off(fs_info);
-		if (ret) {
-			btrfs_put_block_group(cache);
-			break;
-		}
+		ro_set = !ret;
 
 		dev_replace->cursor_right = found_key.offset + length;
 		dev_replace->cursor_left = found_key.offset;
@@ -3660,7 +3658,8 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
 
 		scrub_pause_off(fs_info);
 
-		btrfs_dec_block_group_ro(root, cache);
+		if (ro_set)
+			btrfs_dec_block_group_ro(root, cache);
 
 		btrfs_put_block_group(cache);
 		if (ret)
-- 
1.8.5.1

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