Re: [PATCH] Btrfs: only do the tree_mod_log_free_eb if this is our last ref

[Liu Bo <bo.li.liu@oracle.com>]

On Mon, Jul 01, 2013 at 04:12:27PM -0400, Josef Bacik wrote:
> There is another bug in the tree mod log stuff in that we're calling
> tree_mod_log_free_eb every single time a block is cow'ed.  The problem with this
> is that if this block is shared by multiple snapshots we will call this multiple
> times per block, so if we go to rewind the mod log for this block we'll BUG_ON()
> in __tree_mod_log_rewind because we try to rewind a free twice.  We only want to
> call tree_mod_log_free_eb if we are actually freeing the block.  With this patch
> I no longer hit the panic in __tree_mod_log_rewind.  Thanks,

This fixes my reproducer for __tree_mod_log_rewind() BUG_ON in line 1183.

Tested-by: Liu Bo <bo.li.liu@oracle.com>

> 
> Signed-off-by: Josef Bacik <jbacik@fusionio.com>
> ---
>  fs/btrfs/ctree.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 32e30ad..127e1fd 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -1093,7 +1093,8 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
>  		btrfs_set_node_ptr_generation(parent, parent_slot,
>  					      trans->transid);
>  		btrfs_mark_buffer_dirty(parent);
> -		tree_mod_log_free_eb(root->fs_info, buf);
> +		if (last_ref)
> +			tree_mod_log_free_eb(root->fs_info, buf);
>  		btrfs_free_tree_block(trans, root, buf, parent_start,
>  				      last_ref);
>  	}
> -- 
> 1.7.7.6
> 
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