netdev - Re: [PATCH net-next] mlxsw: spectrum_router: fix xa

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Message-ID: <8734kxix77.fsf@nvidia.com>
Date: Tue, 15 Oct 2024 10:06:19 +0200
From: Petr Machata <petrm@...dia.com>
To: Yuan Can <yuancan@...wei.com>
CC: <idosch@...dia.com>, <petrm@...dia.com>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] mlxsw: spectrum_router: fix xa_store() error
 checking


Yuan Can <yuancan@...wei.com> writes:

> It is meant to use xa_err() to extract the error encoded in the return
> value of xa_store().
>
> Fixes: 44c2fbebe18a ("mlxsw: spectrum_router: Share nexthop counters in resilient groups")
> Signed-off-by: Yuan Can <yuancan@...wei.com>

Reviewed-by: Petr Machata <petrm@...dia.com>

What's the consequence of using IS_ERR()/PTR_ERR() vs. xa_err()? From
the documentation it looks like IS_ERR() might interpret some valid
pointers as errors[0]. Which would then show as leaks, because we bail
out early and never clean up?

I.e. should this aim at net rather than net-next? It looks like it's not
just semantics, but has actual observable impact.

[0] "The XArray does not support storing IS_ERR() pointers as some
    conflict with value entries or internal entries."

> ---
>  drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> index 800dfb64ec83..7d6d859cef3f 100644
> --- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> +++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> @@ -3197,7 +3197,6 @@ mlxsw_sp_nexthop_sh_counter_get(struct mlxsw_sp *mlxsw_sp,
>  {
>  	struct mlxsw_sp_nexthop_group *nh_grp = nh->nhgi->nh_grp;
>  	struct mlxsw_sp_nexthop_counter *nhct;
> -	void *ptr;
>  	int err;
>  
>  	nhct = xa_load(&nh_grp->nhgi->nexthop_counters, nh->id);
> @@ -3210,12 +3209,10 @@ mlxsw_sp_nexthop_sh_counter_get(struct mlxsw_sp *mlxsw_sp,
>  	if (IS_ERR(nhct))
>  		return nhct;
>  
> -	ptr = xa_store(&nh_grp->nhgi->nexthop_counters, nh->id, nhct,
> -		       GFP_KERNEL);
> -	if (IS_ERR(ptr)) {
> -		err = PTR_ERR(ptr);
> +	err = xa_err(xa_store(&nh_grp->nhgi->nexthop_counters, nh->id, nhct,
> +			      GFP_KERNEL));
> +	if (err)
>  		goto err_store;
> -	}