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

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Date:   Tue, 18 Aug 2020 11:37:45 +0200
From:   Petr Machata <petrm@...dia.com>
To:     Ido Schimmel <idosch@...sch.org>
CC:     Bjorn Helgaas <helgaas@...nel.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


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.