Re: [PATCH 10/12] xfs: make xfs_*read_agf return EAGAIN to ALLOC_FLAG_TRYLOCK callers

From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org, hch@infradead.org, david@fromorbit.com
Subject: Re: [PATCH 10/12] xfs: make xfs_*read_agf return EAGAIN to ALLOC_FLAG_TRYLOCK callers
Date: Fri, 24 Jan 2020 15:12:07 -0800	[thread overview]
Message-ID: <20200124231207.GD20014@infradead.org> (raw)
In-Reply-To: <157984320125.3139258.966527323692871610.stgit@magnolia>

On Thu, Jan 23, 2020 at 09:20:01PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Refactor xfs_read_agf and xfs_alloc_read_agf to return EAGAIN if the
> caller passed TRYLOCK and we weren't able to get the lock; and change
> the callers to recognize this.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/libxfs/xfs_alloc.c |   36 ++++++++++++++----------------------
>  fs/xfs/libxfs/xfs_bmap.c  |   11 ++++++-----
>  fs/xfs/xfs_filestream.c   |   11 +++++------
>  3 files changed, 25 insertions(+), 33 deletions(-)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index 34b65635ee34..d8053bc96c4d 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -2502,12 +2502,11 @@ xfs_alloc_fix_freelist(
>  
>  	if (!pag->pagf_init) {
>  		error = xfs_alloc_read_agf(mp, tp, args->agno, flags, &agbp);
> -		if (error)
> +		if (error) {
> +			/* Couldn't lock the AGF so skip this AG. */
> +			if (error == -EAGAIN)
> +				error = 0;
>  			goto out_no_agbp;
> -		if (!pag->pagf_init) {
> -			ASSERT(flags & XFS_ALLOC_FLAG_TRYLOCK);
> -			ASSERT(!(flags & XFS_ALLOC_FLAG_FREEING));
> -			goto out_agbp_relse;
>  		}
>  	}
>  
> @@ -2533,11 +2532,10 @@ xfs_alloc_fix_freelist(
>  	 */
>  	if (!agbp) {
>  		error = xfs_alloc_read_agf(mp, tp, args->agno, flags, &agbp);
> -		if (error)
> -			goto out_no_agbp;
> -		if (!agbp) {
> -			ASSERT(flags & XFS_ALLOC_FLAG_TRYLOCK);
> -			ASSERT(!(flags & XFS_ALLOC_FLAG_FREEING));
> +		if (error) {
> +			/* Couldn't lock the AGF so skip this AG. */
> +			if (error == -EAGAIN)
> +				error = 0;
>  			goto out_no_agbp;
>  		}
>  	}
> @@ -2768,11 +2766,10 @@ xfs_alloc_pagf_init(
>  	xfs_buf_t		*bp;
>  	int			error;
>  
> -	if ((error = xfs_alloc_read_agf(mp, tp, agno, flags, &bp)))
> -		return error;
> -	if (bp)
> +	error = xfs_alloc_read_agf(mp, tp, agno, flags, &bp);
> +	if (!error)
>  		xfs_trans_brelse(tp, bp);
> -	return 0;
> +	return error;
>  }
>  
>  /*
> @@ -2961,12 +2958,6 @@ xfs_read_agf(
>  	error = xfs_trans_read_buf(mp, tp, mp->m_ddev_targp,
>  			XFS_AG_DADDR(mp, agno, XFS_AGF_DADDR(mp)),
>  			XFS_FSS_TO_BB(mp, 1), flags, bpp, &xfs_agf_buf_ops);
> -	/*
> -	 * Callers of xfs_read_agf() currently interpret a NULL bpp as EAGAIN
> -	 * and need to be converted to check for EAGAIN specifically.
> -	 */
> -	if (error == -EAGAIN)
> -		return 0;
>  	if (error)
>  		return error;
>  
> @@ -2992,14 +2983,15 @@ xfs_alloc_read_agf(
>  
>  	trace_xfs_alloc_read_agf(mp, agno);
>  
> +	/* We don't support trylock when freeing. */
> +	ASSERT((flags & (XFS_ALLOC_FLAG_FREEING | XFS_ALLOC_FLAG_TRYLOCK)) !=
> +			(XFS_ALLOC_FLAG_FREEING | XFS_ALLOC_FLAG_TRYLOCK));

Does this assert really work?  Shouldn't it be

	ASSERT(!(flags & XFS_ALLOC_FLAG_FREEING) ||
	       !(flags & XFS_ALLOC_FLAG_TRYLOCK));

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>