Re: [PATCH] mkfs: avoid divide-by-zero when hardware reports optimal i/o size as 0

[Carlos Maiolino <cmaiolino@redhat.com>]

On Thu, Jul 19, 2018 at 05:23:22PM -0400, Jeff Mahoney wrote:
> Commit 051b4e37f5e (mkfs: factor AG alignment) factored out the
> AG alignment code into a separate function.  It got rid of
> redundant checks for dswidth != 0 since calc_stripe_factors was
> supposed to guarantee that if dsunit is non-zero dswidth will be
> as well.  Unfortunately, there's hardware out there that reports its
> optimal i/o size as larger than the maximum i/o size, which the kernel
> treats as broken and zeros out the optimal i/o size.  We'll accept
> the multi-sector dsunit but have a zero dswidth and hit a divide-by-zero
> in align_ag_geometry.
> 
> To resolve this we can check the topology before consuming it, default
> to using the stripe unit as the stripe width, and warn the user about it.
> 

I wonder if this shouldn't go into blkid_get_topology since something is wrong
with the information reported by the storage.
And require a force_overwrite to continue, at this point, something looks quite
wrong in the storage, and I think this is the last 'resource' a sysadmin will
have to notice this before making the FS, and start using it, so, maybe requiring
force_overwrite would bring more attention.

> Fixes: 051b4e37f5e (mkfs: factor AG alignment)
> Signed-off-by: Jeff Mahoney <jeffm@suse.com>
> ---
>  mkfs/xfs_mkfs.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> index a135e06e..35542e57 100644
> --- a/mkfs/xfs_mkfs.c
> +++ b/mkfs/xfs_mkfs.c
> @@ -2295,6 +2295,12 @@ _("data stripe width (%d) must be a multiple of the data stripe unit (%d)\n"),
>  	if (!dsunit) {
>  		dsunit = ft->dsunit;
>  		dswidth = ft->dswidth;
> +		if (dsunit && dswidth == 0) {
> +			fprintf(stderr,
> +_("%s: Volume reports stripe unit of %d bytes but stripe width of 0.  Using stripe width of %d bytes, which may not be optimal.\n"),
> +				progname, dsunit << 9, dsunit << 9);
> +			dswidth = dsunit;
> +		}
>  		use_dev = true;
>  	} else {
>  		/* check and warn is alignment is sub-optimal */
> -- 
> 2.16.4
> 
> 
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-- 
Carlos