linux-kernel - Re: [PATCH][next] mlxsw: spectrum_router: remove redundant initialization of variable force

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Message-ID: <YGF+D6fXNIbNVzff@shredder.lan>
Date:   Mon, 29 Mar 2021 10:13:19 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     Colin King <colin.king@...onical.com>
Cc:     Jiri Pirko <jiri@...dia.com>, Ido Schimmel <idosch@...dia.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        petrm@...dia.com
Subject: Re: [PATCH][next] mlxsw: spectrum_router: remove redundant
 initialization of variable force

On Sat, Mar 27, 2021 at 10:33:34PM +0000, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The variable force is being initialized with a value that is
> never read and it is being updated later with a new value. The
> initialization is redundant and can be removed.
> 
> Addresses-Coverity: ("Unused value")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> index 6ccaa194733b..ff240e3c29f7 100644
> --- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> +++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> @@ -5059,7 +5059,7 @@ mlxsw_sp_nexthop_obj_bucket_adj_update(struct mlxsw_sp *mlxsw_sp,
>  {
>  	u16 bucket_index = info->nh_res_bucket->bucket_index;
>  	struct netlink_ext_ack *extack = info->extack;
> -	bool force = info->nh_res_bucket->force;
> +	bool force;

Actually, there is a bug to be fixed here:

```
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
index 6ccaa194733b..41259c0004d1 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
@@ -5068,8 +5068,9 @@ mlxsw_sp_nexthop_obj_bucket_adj_update(struct mlxsw_sp *mlxsw_sp,
        /* No point in trying an atomic replacement if the idle timer interval
         * is smaller than the interval in which we query and clear activity.
         */
-       force = info->nh_res_bucket->idle_timer_ms <
-               MLXSW_SP_NH_GRP_ACTIVITY_UPDATE_INTERVAL;
+       if (!force && info->nh_res_bucket->idle_timer_ms <
+           MLXSW_SP_NH_GRP_ACTIVITY_UPDATE_INTERVAL)
+               force = true;
 
        adj_index = nh->nhgi->adj_index + bucket_index;
        err = mlxsw_sp_nexthop_update(mlxsw_sp, adj_index, nh, force, ratr_pl);
```

We should only fallback to a non-atomic replacement when the current
replacement is atomic and the idle timer is too short.

We currently ignore the value of 'force'. This means that a non-atomic
replacement ('force' is true) can be made atomic if idle timer is larger
than 1 second.

Colin, do you mind if I submit it formally as a fix later this week? I
want to run it through our usual process. Will mention you in
Reported-by, obviously.

>  	char ratr_pl_new[MLXSW_REG_RATR_LEN];
>  	char ratr_pl[MLXSW_REG_RATR_LEN];
>  	u32 adj_index;
> -- 
> 2.30.2
>