Re: [PATCH 2/4] xfs: xfs_alloc_file_space() fails to detect ENOSPC

["Darrick J. Wong" <djwong@kernel.org>]

[explicitly cc hch]

On Wed, Apr 03, 2024 at 08:38:17AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> xfs_alloc_file_space ends up in an endless loop when
> xfs_bmapi_write() returns nimaps == 0 at ENOSPC. The process is
> unkillable, and so just runs around in a tight circle burning CPU
> until the system is rebooted.
> 
> This is a regression introduced by commit 35dc55b9e80c ("xfs: handle
> nimaps=0 from xfs_bmapi_write in xfs_alloc_file_space") which
> specifically removed ENOSPC detection from xfs_alloc_file_space()
> and replaces it with an endless loop. This attempts to fix an issue
> converting a delalloc extent when not enough contiguous free space
> is available to convert the entire delalloc extent.
> 
> Right now just revert the change as it only manifested on code under
> development and isn't currently a real-world problem.
> 
> Fixes: 35dc55b9e80c ("xfs: handle nimaps=0 from xfs_bmapi_write in xfs_alloc_file_space")

Shouldn't Christoph be cc'd if you're reverting his patch?

> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_bmap_util.c | 18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 19e11d1da660..262557735d4d 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -735,19 +735,13 @@ xfs_alloc_file_space(
>  		if (error)
>  			break;
>  
> -		/*
> -		 * If the allocator cannot find a single free extent large
> -		 * enough to cover the start block of the requested range,
> -		 * xfs_bmapi_write will return 0 but leave *nimaps set to 0.
> -		 *
> -		 * In that case we simply need to keep looping with the same
> -		 * startoffset_fsb so that one of the following allocations
> -		 * will eventually reach the requested range.
> -		 */
> -		if (nimaps) {
> -			startoffset_fsb += imapp->br_blockcount;
> -			allocatesize_fsb -= imapp->br_blockcount;
> +		if (nimaps == 0) {
> +			error = ENOSPC;

-ENOSPC.

--D

> +			break;
>  		}
> +
> +		startoffset_fsb += imapp->br_blockcount;
> +		allocatesize_fsb -= imapp->br_blockcount;
>  	}
>  
>  	return error;
> -- 
> 2.43.0
> 
>