Re: [PATCH v2 2/4] xfs: add an error tag to inject a ->writeback_submit() failure

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

On Thu, Sep 24, 2026 at 11:11:52AM +0200, Andrea Parri wrote:
> The only in-tree way for xfs_writeback_submit() to fail is a failing
> xfs_reflink_convert_cow(), which requires a shared (reflinked) CoW
> extent.  There was previously no way to exercise that failure path
> from userspace, which made it hard to write an xfstest for it, e.g.
> for "iomap: don't resubmit an ioend after ->writeback_submit()
> failed".
> 
> Add XFS_ERRTAG_WB_COW_CONVERT_ERROR to force xfs_reflink_convert_cow()
> to fail with -EIO, so that ->writeback_submit() failure and its
> callers' error handling can be exercised with error injection alone,
> without needing a corrupted or racy COW fork.
> 
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Assisted-by: LLM
> Signed-off-by: Andrea Parri <parri.andrea@gmail.com>

Looks good to me,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/xfs/libxfs/xfs_errortag.h | 6 ++++--
>  fs/xfs/xfs_reflink.c         | 5 +++++
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_errortag.h b/fs/xfs/libxfs/xfs_errortag.h
> index 6de207fed2d89..e6b0864051b0a 100644
> --- a/fs/xfs/libxfs/xfs_errortag.h
> +++ b/fs/xfs/libxfs/xfs_errortag.h
> @@ -75,7 +75,8 @@
>  #define XFS_ERRTAG_METAFILE_RESV_CRITICAL		45
>  #define XFS_ERRTAG_FORCE_ZERO_RANGE			46
>  #define XFS_ERRTAG_ZONE_RESET				47
> -#define XFS_ERRTAG_MAX					48
> +#define XFS_ERRTAG_WB_COW_CONVERT_ERROR		48
> +#define XFS_ERRTAG_MAX					49
>  
>  /*
>   * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
> @@ -137,7 +138,8 @@ XFS_ERRTAG(WRITE_DELAY_MS,	write_delay_ms,		3000) \
>  XFS_ERRTAG(EXCHMAPS_FINISH_ONE,	exchmaps_finish_one,	1) \
>  XFS_ERRTAG(METAFILE_RESV_CRITICAL, metafile_resv_crit,	4) \
>  XFS_ERRTAG(FORCE_ZERO_RANGE,	force_zero_range,	4) \
> -XFS_ERRTAG(ZONE_RESET,		zone_reset,		1)
> +XFS_ERRTAG(ZONE_RESET,		zone_reset,		1) \
> +XFS_ERRTAG(WB_COW_CONVERT_ERROR, wb_cow_convert_error,	1)
>  #endif /* XFS_ERRTAG */
>  
>  #endif /* __XFS_ERRORTAG_H_ */
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 4801361366359..104542b10d9e0 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -34,6 +34,8 @@
>  #include "xfs_rtalloc.h"
>  #include "xfs_rtgroup.h"
>  #include "xfs_metafile.h"
> +#include "xfs_errortag.h"
> +#include "xfs_error.h"
>  
>  /*
>   * Copy on Write of Shared Blocks
> @@ -346,6 +348,9 @@ xfs_reflink_convert_cow(
>  
>  	ASSERT(count != 0);
>  
> +	if (XFS_TEST_ERROR(mp, XFS_ERRTAG_WB_COW_CONVERT_ERROR))
> +		return -EIO;
> +
>  	xfs_ilock(ip, XFS_ILOCK_EXCL);
>  	error = xfs_reflink_convert_cow_locked(ip, offset_fsb, count_fsb);
>  	xfs_iunlock(ip, XFS_ILOCK_EXCL);
> -- 
> 2.53.0
> 
>