Re: [PATCH] Btrfs: do not abort transaction at btrfs_update_root() after failure to COW path

[Anand Jain <anand.jain@oracle.com>]

On 29/4/19 8:08 PM, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> Currently when we fail to COW a path at btrfs_update_root() we end up
> always aborting the transaction. However all the current callers of
> btrfs_update_root() are able to deal with errors returned from it, many do
> end up aborting the transaction themselves (directly or not, such as the
> transaction commit path), other BUG_ON() or just gracefully cancel whatever
> they were doing.
> 
> When syncing the fsync log, we call btrfs_update_root() through
> tree-log.c:update_log_root(), and if it returns an -ENOSPC error, the log
> sync code does not abort the transaction, instead it gracefully handles
> the error and returns -EAGAIN to the fsync handler, so that it falls back
> to a transaction commit. Any other error different from -ENOSPC, makes the
> log sync code abort the transaction.
> 
> So remove the transaction abort from btrfs_update_log() when we fail to
> COW a path to update the root item, so that if an -ENOSPC failure happens
> we avoid aborting the current transaction and have a chance of the fsync
> succeeding after falling back to a transaction commit.
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203413
> Fixes: 79787eaab46121 ("btrfs: replace many BUG_ONs with proper error handling")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>


Reviewed-by: Anand Jain <anand.jain@oracle.com>


> ---
>   fs/btrfs/root-tree.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
> index 893d12fbfda0..1a92ad546f91 100644
> --- a/fs/btrfs/root-tree.c
> +++ b/fs/btrfs/root-tree.c
> @@ -132,10 +132,8 @@ int btrfs_update_root(struct btrfs_trans_handle *trans, struct btrfs_root
>   		return -ENOMEM;
>   
>   	ret = btrfs_search_slot(trans, root, key, path, 0, 1);
> -	if (ret < 0) {
> -		btrfs_abort_transaction(trans, ret);
> +	if (ret < 0)
>   		goto out;
> -	}
>   
>   	if (ret != 0) {
>   		btrfs_print_leaf(path->nodes[0]);
>