Re: [RFC PATCH] xfs/179: modify test to trigger refcount update bugs

[Dave Chinner <david@fromorbit.com>]

On Tue, Nov 29, 2022 at 02:06:39PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Upon enabling fsdax + reflink for XFS, this test began to report
> refcount metadata corruptions after being run.  Specifically, xfs_repair
> noticed single-block refcount records that could be combined but had not
> been.
> 
> The root cause of this is improper MAXREFCOUNT edge case handling in
> xfs_refcount_merge_extents.  When we're trying to find candidates for a
> record merge, we compute the refcount of the merged record, but without
> accounting for the fact that once a record hits rc_refcount ==
> MAXREFCOUNT, it is pinned that way forever.
> 
> Adjust this test to use a sub-filesize write for one of the COW writes,
> because this is how we force the extent merge code to run.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>

Seems like a reasonable modification to the test....

> ---
>  tests/xfs/179 |   28 +++++++++++++++++++++++++---
>  1 file changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/tests/xfs/179 b/tests/xfs/179
> index ec0cb7e5b4..214558f694 100755
> --- a/tests/xfs/179
> +++ b/tests/xfs/179
> @@ -21,17 +21,28 @@ _require_scratch_nocheck
>  _require_cp_reflink
>  _require_test_program "punch-alternating"
>  
> +_fixed_by_kernel_commit XXXXXXXXXXXX "xfs: estimate post-merge refcounts correctly"

Though I really don't like these annotation because when the test
fails in future as I'm developing new code it's going to tell me I
need a fix I already have in the kernel. This is just extra noise
that I have to filter out of the results output. IMO a comment for
this information or a line in the commit message is fine - it
just doesn't belong in the test output....

Other than that:

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com