netdev - Re: [PATCH net-next 03/11] mlxsw: spectrum

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Date:   Tue, 18 Aug 2020 07:10:04 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Petr Machata <petrm@...dia.com>
Cc:     Ido Schimmel <idosch@...sch.org>, netdev@...r.kernel.org,
        davem@...emloft.net, kuba@...nel.org, jiri@...lanox.com,
        mlxsw@...lanox.com, Ido Schimmel <idosch@...lanox.com>
Subject: Re: [PATCH net-next 03/11] mlxsw: spectrum_policer: Add policer core

On Tue, Aug 18, 2020 at 11:37:45AM +0200, Petr Machata wrote:
> Ido Schimmel <idosch@...sch.org> writes:
> > On Mon, Aug 17, 2020 at 10:38:24AM -0500, Bjorn Helgaas wrote:
> >> You've likely seen this already, but Coverity found this problem:
> >> 
> >>   *** CID 1466147:  Control flow issues  (DEADCODE)
> >>   /drivers/net/ethernet/mellanox/mlxsw/spectrum_policer.c: 380 in mlxsw_sp_policers_init()
> >>   374     	}
> >>   375     
> >>   376     	return 0;
> >>   377     
> >>   378     err_family_register:
> >>   379     	for (i--; i >= 0; i--) {
> >>   >>>     CID 1466147:  Control flow issues  (DEADCODE)
> >>   >>>     Execution cannot reach this statement: "struct mlxsw_sp_policer_fam...".
> >>   380     		struct mlxsw_sp_policer_family *family;
> >>   381     
> >>   382     		family = mlxsw_sp->policer_core->family_arr[i];
> >>   383     		mlxsw_sp_policer_family_unregister(mlxsw_sp, family);
> >>   384     	}
> >>   385     err_init:
> >> 
> >> I think the problem is that MLXSW_SP_POLICER_TYPE_MAX is 0 because
> >> 
> >> > +enum mlxsw_sp_policer_type {
> >> > +	MLXSW_SP_POLICER_TYPE_SINGLE_RATE,
> >> > +
> >> > +	__MLXSW_SP_POLICER_TYPE_MAX,
> >> > +	MLXSW_SP_POLICER_TYPE_MAX = __MLXSW_SP_POLICER_TYPE_MAX - 1,
> >> > +};
> >> 
> >> so we can only execute the family_register loop once, with i == 0,
> >> and if we get to err_family_register via the error exit:
> >> 
> >> > +	for (i = 0; i < MLXSW_SP_POLICER_TYPE_MAX + 1; i++) {
> >> > +		err = mlxsw_sp_policer_family_register(mlxsw_sp, mlxsw_sp_policer_family_arr[i]);
> >> > +		if (err)
> >> > +			goto err_family_register;
> >> 
> >> i will be 0, so i-- sets i to -1, so we don't enter the
> >> family_unregister loop body since -1 is not >= 0.
> >
> > Thanks for the report, but isn't the code doing the right thing here? I
> > mean, it's dead code now, but as soon as we add another family it will
> > be executed. It seems error prone to remove it only to please Coverity
> > and then add it back when it's actually needed.
> 
> Agreed.

You're right, I missed the forest for the trees.  Sorry for the noise.

Bjorn