Re: [PATCH 4.9 083/116] btrfs: free block groups after freeing fs trees

[David Sterba]

On Thu, Feb 13, 2020 at 07:20:27AM -0800, Greg Kroah-Hartman wrote:
> From: Josef Bacik <josef@xxxxxxxxxxxxxx>
> 
> [ Upstream commit 4e19443da1941050b346f8fc4c368aa68413bc88 ]
> 
> Sometimes when running generic/475 we would trip the
> WARN_ON(cache->reserved) check when free'ing the block groups on umount.
> This is because sometimes we don't commit the transaction because of IO
> errors and thus do not cleanup the tree logs until at umount time.
> 
> These blocks are still reserved until they are cleaned up, but they
> aren't cleaned up until _after_ we do the free block groups work.  Fix
> this by moving the free after free'ing the fs roots, that way all of the
> tree logs are cleaned up and we have a properly cleaned fs.  A bunch of
> loops of generic/475 confirmed this fixes the problem.
> 
> CC: stable@xxxxxxxxxxxxxxx # 4.9+
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Reviewed-by: David Sterba <dsterba@xxxxxxxx>
> Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  fs/btrfs/disk-io.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index eab5a9065f093..439b5f5dc3274 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -3864,6 +3864,15 @@ void close_ctree(struct btrfs_root *root)
>  	clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
>  	free_root_pointers(fs_info, true);
>  
> +	/*
> +	 * We must free the block groups after dropping the fs_roots as we could
> +	 * have had an IO error and have left over tree log blocks that aren't
> +	 * cleaned up until the fs roots are freed.  This makes the block group
> +	 * accounting appear to be wrong because there's pending reserved bytes,
> +	 * so make sure we do the block group cleanup afterwards.
> +	 */
> +	btrfs_free_block_groups(fs_info);

Something's wrong here.  The patch 4e19443da1 moves the
btrfs_free_block_groups() call and the stable backport lacks the "-"
line. However the patch applies cleanly on 4.9.213.

3855         btrfs_free_block_groups(fs_info);
^^^^

3856
3857         /*
3858          * we must make sure there is not any read request to
3859          * submit after we stopping all workers.
3860          */
3861         invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
3862         btrfs_stop_all_workers(fs_info);
3863
3864         clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
3865         free_root_pointers(fs_info, 1);
3866
3867         /*
3868          * We must free the block groups after dropping the fs_roots as we could
3869          * have had an IO error and have left over tree log blocks that aren't
3870          * cleaned up until the fs roots are freed.  This makes the block group
3871          * accounting appear to be wrong because there's pending reserved bytes,
3872          * so make sure we do the block group cleanup afterwards.
3873          */
3874         btrfs_free_block_groups(fs_info);

The first one should not be there.