Re: [PATCH] Btrfs: fix ASSERT(list_empty(&cur_trans->dirty_bgs_list)

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

On Mon, Mar 02, 2015 at 12:46:55PM -0500, Josef Bacik wrote:
> Dave could hit this assert consistently running btrfs/078.  This is because
> when we update the block groups we could truncate the free space, which would
> try to delete the csums for that range and dirty the csum root.  For this to
> happen we have to have already written out the csum root so it's kind of hard to
> hit this case.  This patch fixes this by changing the logic to only write the
> dirty block groups if the dirty_cowonly_roots list is empty.  This will get us
> the same effect as before since we add the extent root last, and will cover the
> case that we dirty some other root again but not the extent root.  Thanks,

Free space inode is NODATASUM, so its searching csum tree in
__btrfs_free_extent() is really unnecessary, by skipping that, csum tree
won't be inserted into dirty_cowonly_roots list again, so it also passed btrfs/078,
at least on my box.

Thanks,

-liubo

> 
> Reported-by: David Sterba <dsterba@suse.cz>
> Signed-off-by: Josef Bacik <jbacik@fb.com>
> ---
>  fs/btrfs/transaction.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
> index 038fcf6..a7a413f 100644
> --- a/fs/btrfs/transaction.c
> +++ b/fs/btrfs/transaction.c
> @@ -1023,16 +1023,22 @@ static int update_cowonly_root(struct btrfs_trans_handle *trans,
>  	u64 old_root_bytenr;
>  	u64 old_root_used;
>  	struct btrfs_root *tree_root = root->fs_info->tree_root;
> -	bool extent_root = (root->objectid == BTRFS_EXTENT_TREE_OBJECTID);
> +	struct btrfs_fs_info *fs_info = root->fs_info;
>  
>  	old_root_used = btrfs_root_used(&root->root_item);
>  	btrfs_write_dirty_block_groups(trans, root);
>  
>  	while (1) {
>  		old_root_bytenr = btrfs_root_bytenr(&root->root_item);
> +
> +		/*
> +		 * We can only break out if our root matches the root item and
> +		 * we either have more roots to process or we have no more roots
> +		 * to process and there are no empty bgs.
> +		 */
>  		if (old_root_bytenr == root->node->start &&
>  		    old_root_used == btrfs_root_used(&root->root_item) &&
> -		    (!extent_root ||
> +		    (!list_empty(&fs_info->dirty_cowonly_roots) ||
>  		     list_empty(&trans->transaction->dirty_bgs)))
>  			break;
>  
> @@ -1044,7 +1050,7 @@ static int update_cowonly_root(struct btrfs_trans_handle *trans,
>  			return ret;
>  
>  		old_root_used = btrfs_root_used(&root->root_item);
> -		if (extent_root) {
> +		if (list_empty(&fs_info->dirty_cowonly_roots)) {
>  			ret = btrfs_write_dirty_block_groups(trans, root);
>  			if (ret)
>  				return ret;
> -- 
> 1.8.3.1
> 
> --
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