[PATCH v3] btrfs-progs: Don't BUG_ON() when write_dev_supers() fails

[Qu Wenruo <wqu@suse.com>]

[BUG]
Since commit "btrfs-progs: disk-io: Flush to ensure super block write is
FUA" mkfs-tests/017 will fail like:

  ====== RUN MUSTFAIL /home/adam/btrfs-progs/mkfs.btrfs -K -f /dev/mapper/btrfs-progs-thin-vol
  ERROR: failed to write super block for devid 1: flush error: Input/output error
  disk-io.c:1810: write_all_supers: BUG_ON `ret` triggered, value -5
  /home/adam/btrfs-progs/mkfs.btrfs(+0x1e5c1)[0x557a2c83e5c1]
  /home/adam/btrfs-progs/mkfs.btrfs(+0x1e65f)[0x557a2c83e65f]
  /home/adam/btrfs-progs/mkfs.btrfs(write_all_supers+0x1ce)[0x557a2c843a8a]
  /home/adam/btrfs-progs/mkfs.btrfs(write_ctree_super+0x12d)[0x557a2c843be2]
  /home/adam/btrfs-progs/mkfs.btrfs(btrfs_commit_transaction+0x250)[0x557a2c887c56]
  /home/adam/btrfs-progs/mkfs.btrfs(+0xc0b1)[0x557a2c82c0b1]
  /home/adam/btrfs-progs/mkfs.btrfs(main+0x1049)[0x557a2c82e929]
  /usr/lib/libc.so.6(__libc_start_main+0xf3)[0x7f6689e99223]
  /home/adam/btrfs-progs/mkfs.btrfs(_start+0x2e)[0x557a2c82b86e]
  failed (expected): /home/adam/btrfs-progs/mkfs.btrfs -K -f /dev/mapper/btrfs-progs-thin-vol

[CAUSE]
Just one BUG_ON() in write_all_supers().

[FIX]
Just remove the BUG_ON(). Callers of write_all_supers() are already
checking the return value.

Also since write_all_supers() can return error, make write_ctree_super()
callers, btrfs_commit_transaction() and close_ctree_fs_info() to
handle the error correctly.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v2:
- Make write_ctree_super() callers to handle the error properly.
v3:
- Use skip_commit label to skip unnecessary super block write.
---
 disk-io.c     | 9 +++++++--
 transaction.c | 2 +-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/disk-io.c b/disk-io.c
index 10550151c5bb..151eb3b5a278 100644
--- a/disk-io.c
+++ b/disk-io.c
@@ -1807,7 +1807,8 @@ int write_all_supers(struct btrfs_fs_info *fs_info)
 		btrfs_set_super_flags(sb, flags | BTRFS_HEADER_FLAG_WRITTEN);
 
 		ret = write_dev_supers(fs_info, sb, dev);
-		BUG_ON(ret);
+		if (ret < 0)
+			return ret;
 	}
 	return 0;
 }
@@ -1863,8 +1864,12 @@ int close_ctree_fs_info(struct btrfs_fs_info *fs_info)
 		BUG_ON(ret);
 		ret = __commit_transaction(trans, root);
 		BUG_ON(ret);
-		write_ctree_super(trans);
+		ret = write_ctree_super(trans);
 		kfree(trans);
+		if (ret) {
+			err = ret;
+			goto skip_commit;
+		}
 	}
 
 	if (fs_info->finalize_on_close) {
diff --git a/transaction.c b/transaction.c
index e756db332fec..3a63988b0969 100644
--- a/transaction.c
+++ b/transaction.c
@@ -197,7 +197,7 @@ commit_tree:
 	__commit_transaction(trans, root);
 	if (ret < 0)
 		goto out;
-	write_ctree_super(trans);
+	ret = write_ctree_super(trans);
 	btrfs_finish_extent_commit(trans, fs_info->extent_root,
 			           &fs_info->pinned_extents);
 	kfree(trans);
-- 
2.21.0