Re: [PATCH v6 7/7] xfs: add error injection for per-AG resv failure when shrinkfs

[Brian Foster <bfoster@redhat.com>]

On Tue, Jan 26, 2021 at 08:56:21PM +0800, Gao Xiang wrote:
> per-AG resv failure after fixing up freespace is hard to test in an
> effective way, so directly add an error injection path to observe
> such error handling path works as expected.
> 
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> ---
>  fs/xfs/libxfs/xfs_ag.c       | 5 +++++
>  fs/xfs/libxfs/xfs_errortag.h | 4 +++-
>  fs/xfs/xfs_error.c           | 2 ++
>  3 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> index c6e68e265269..5076913c153f 100644
> --- a/fs/xfs/libxfs/xfs_ag.c
> +++ b/fs/xfs/libxfs/xfs_ag.c
> @@ -23,6 +23,7 @@
>  #include "xfs_ag_resv.h"
>  #include "xfs_health.h"
>  #include "xfs_error.h"
> +#include "xfs_errortag.h"
>  #include "xfs_bmap.h"
>  #include "xfs_defer.h"
>  #include "xfs_log_format.h"
> @@ -559,6 +560,10 @@ xfs_ag_shrink_space(
>  	be32_add_cpu(&agf->agf_length, -len);
>  
>  	err2 = xfs_ag_resv_init(agibp->b_pag, *tpp);
> +
> +	if (XFS_TEST_ERROR(false, mp, XFS_ERRTAG_SHRINKFS_AG_RESV_FAIL))
> +		err2 = -ENOSPC;
> +

Seems reasonable, but I feel like this could be broadened to serve as a
generic perag reservation error tag. I suppose we might not be able to
use it on a clean mount, but perhaps it could be reused for growfs and
remount. Hm?

Brian

>  	if (err2) {
>  		be32_add_cpu(&agi->agi_length, len);
>  		be32_add_cpu(&agf->agf_length, len);
> diff --git a/fs/xfs/libxfs/xfs_errortag.h b/fs/xfs/libxfs/xfs_errortag.h
> index 6ca9084b6934..5fd71a930b68 100644
> --- a/fs/xfs/libxfs/xfs_errortag.h
> +++ b/fs/xfs/libxfs/xfs_errortag.h
> @@ -40,6 +40,7 @@
>  #define XFS_ERRTAG_REFCOUNT_FINISH_ONE			25
>  #define XFS_ERRTAG_BMAP_FINISH_ONE			26
>  #define XFS_ERRTAG_AG_RESV_CRITICAL			27
> +
>  /*
>   * DEBUG mode instrumentation to test and/or trigger delayed allocation
>   * block killing in the event of failed writes. When enabled, all
> @@ -58,7 +59,8 @@
>  #define XFS_ERRTAG_BUF_IOERROR				35
>  #define XFS_ERRTAG_REDUCE_MAX_IEXTENTS			36
>  #define XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT		37
> -#define XFS_ERRTAG_MAX					38
> +#define XFS_ERRTAG_SHRINKFS_AG_RESV_FAIL		38
> +#define XFS_ERRTAG_MAX					39
>  
>  /*
>   * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
> diff --git a/fs/xfs/xfs_error.c b/fs/xfs/xfs_error.c
> index 185b4915b7bf..7bae34bfddd2 100644
> --- a/fs/xfs/xfs_error.c
> +++ b/fs/xfs/xfs_error.c
> @@ -168,6 +168,7 @@ XFS_ERRORTAG_ATTR_RW(iunlink_fallback,	XFS_ERRTAG_IUNLINK_FALLBACK);
>  XFS_ERRORTAG_ATTR_RW(buf_ioerror,	XFS_ERRTAG_BUF_IOERROR);
>  XFS_ERRORTAG_ATTR_RW(reduce_max_iextents,	XFS_ERRTAG_REDUCE_MAX_IEXTENTS);
>  XFS_ERRORTAG_ATTR_RW(bmap_alloc_minlen_extent,	XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT);
> +XFS_ERRORTAG_ATTR_RW(shrinkfs_ag_resv_fail, XFS_ERRTAG_SHRINKFS_AG_RESV_FAIL);
>  
>  static struct attribute *xfs_errortag_attrs[] = {
>  	XFS_ERRORTAG_ATTR_LIST(noerror),
> @@ -208,6 +209,7 @@ static struct attribute *xfs_errortag_attrs[] = {
>  	XFS_ERRORTAG_ATTR_LIST(buf_ioerror),
>  	XFS_ERRORTAG_ATTR_LIST(reduce_max_iextents),
>  	XFS_ERRORTAG_ATTR_LIST(bmap_alloc_minlen_extent),
> +	XFS_ERRORTAG_ATTR_LIST(shrinkfs_ag_resv_fail),
>  	NULL,
>  };
>  
> -- 
> 2.27.0
>