Re: [PATCH 06/11] xfs: flush eof/cowblocks if we can't reserve quota for file blocks

From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 06/11] xfs: flush eof/cowblocks if we can't reserve quota for file blocks
Date: Tue, 19 Jan 2021 08:08:45 +0100	[thread overview]
Message-ID: <YAaFfUxZjXAabnoV@infradead.org> (raw)
In-Reply-To: <161100795124.88816.6644776235251695171.stgit@magnolia>

> @@ -351,13 +351,14 @@ xfs_reflink_allocate_cow(
>  	bool			convert_now)
>  {
>  	struct xfs_mount	*mp = ip->i_mount;
> +	struct xfs_trans	*tp;
>  	xfs_fileoff_t		offset_fsb = imap->br_startoff;
>  	xfs_filblks_t		count_fsb = imap->br_blockcount;
> -	struct xfs_trans	*tp;
> -	int			nimaps, error = 0;
> -	bool			found;
>  	xfs_filblks_t		resaligned;
>  	xfs_extlen_t		resblks = 0;
> +	bool			found;
> +	bool			quota_retry = false;
> +	int			nimaps, error = 0;

Any good reason for reshuffling the declarations here?

> +	if (error) {
> +		/* This function must return with the ILOCK held. */
> +		xfs_ilock(ip, *lockmode);
> +		return error;
> +	}

Ugg.

> +	if (error) {
> +		xfs_trans_cancel(*tpp);
> +		*tpp = NULL;
> +		xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +	}
> +
> +	/* We only allow one retry for EDQUOT/ENOSPC. */
> +	if (*retry || (error != -EDQUOT && error != -ENOSPC)) {
> +		*retry = false;
> +		return error;
> +	}

Id really don't like the semantics where this wrapper unlocks the
ilock.  Keeping all the locking at one layer, which is the callers
makes the code much easier to reason about

> +
> +	/* Try to free some quota for this file's dquots. */
> +	err2 = xfs_blockgc_free_quota(ip, 0, retry);
> +	if (err2)
> +		return err2;
> +	return *retry ? 0 : error;
>  }

Why not have a should_retry helper for the callers and let them call
xfs_blockgc_free_quota?  That is a little more boilerplate code, but
a lot less obsfucated.