Re: [PATCH] xfs: xchk_xattr_listent() fix context->seen_enough to -ECANCELED

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On Wed, Feb 05, 2020 at 01:04:55PM -0600, Bill O'Donnell wrote:
> Commit e7ee96dfb8c (xfs: remove all *_ITER_ABORT values)
> replaced *_ITER_ABORT values with -ECANCELED. The replacement
> in the case of scrub/attr.c xchk_xattr_listent() is in
> error (context->seen_enough = 1;). Instead of '1', use
> the intended -ECANCELED.
> 
> Fixes: e7ee96dfb8c (xfs: remove all *_ITER_ABORT values)
> Signed-off-by: Bill O'Donnell <billodo@xxxxxxxxxx>
> ---
>  fs/xfs/scrub/attr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/scrub/attr.c b/fs/xfs/scrub/attr.c
> index d9f0dd444b80..5d0590f78973 100644
> --- a/fs/xfs/scrub/attr.c
> +++ b/fs/xfs/scrub/attr.c
> @@ -171,7 +171,7 @@ xchk_xattr_listent(
>  					     args.blkno);
>  fail_xref:
>  	if (sx->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
> -		context->seen_enough = 1;

Hmm.  The attr list functions do:

	if (context->seen_enough)
		break;

to stop iteration of the attributes.  Any nonzero value will work,
positive or negative.  Further down in the scrub/attr.c, xchk_xattr
does:

	/* Did our listent function try to return any errors? */
	if (sx.context.seen_enough < 0)
		error = sx.context.seen_enough;

Which means that if seen_enough is set to a negative value, we'll return
that negative value all the way back to userspace, which means that the
userspace buffer is not updated and xfs_scrub will think there was a
runtime error.

> +		context->seen_enough = -ECANCELED;

So this will cause xfs_scrub to abort with "Operation Canceled" if it
found a corruption error.  The patch I sent to the list had -ECANCELED,
but then I noticed the scrub breakage and changed it to 1 before
committing.  Other parts of the attr code use 1 to stop an attr walk
without returning errors to userspace.

Perhaps it's time to replace that novel use of "1" (and audit all the
branching and whatnot) with -ECANCELED so that we can go on cargoculting
negative int errors in peace.

(*UGH* I remembered that I was the one who applied negative int error
semantics to seen_enough in the first place; before that, its meaning
was purely boolean.  It's still screaming for a cleanup though...)

--D

>  	return;
>  }
>  
> -- 
> 2.24.1
> 



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