linux-kernel - Re: [Intel-wired-lan] [PATCH v3] net: ethernet: fix uninitialized pointers with free attribute

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Message-ID: <d614bc7b-a2d9-4213-9bdb-cc43b325c36d@intel.com>
Date: Wed, 19 Nov 2025 12:25:05 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
CC: Ally Heev <allyheev@...il.com>, Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>, Andrew Lunn
	<andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, "Eric
 Dumazet" <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, "K. Y. Srinivasan" <kys@...rosoft.com>, Haiyang Zhang
	<haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, Dexuan Cui
	<decui@...rosoft.com>, Aleksandr Loktionov <aleksandr.loktionov@...el.com>,
	<intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-hyperv@...r.kernel.org>
Subject: Re: [Intel-wired-lan] [PATCH v3] net: ethernet: fix uninitialized
 pointers with free attribute

From: Dan Carpenter <dan.carpenter@...aro.org>
Date: Mon, 17 Nov 2025 21:11:44 +0300

> On Mon, Nov 17, 2025 at 03:37:30PM +0100, Alexander Lobakin wrote:
>> From: Dan Carpenter <dan.carpenter@...aro.org>
>> Date: Mon, 17 Nov 2025 16:11:32 +0300
>>
>>> On Thu, Nov 06, 2025 at 03:07:26PM +0100, Alexander Lobakin wrote:
>>>>> diff --git a/drivers/net/ethernet/intel/ice/ice_flow.c b/drivers/net/ethernet/intel/ice/ice_flow.c
>>>>> index 6d5c939dc8a515c252cd2b77d155b69fa264ee92..3590dacf3ee57879b3809d715e40bb290e40c4aa 100644
>>>>> --- a/drivers/net/ethernet/intel/ice/ice_flow.c
>>>>> +++ b/drivers/net/ethernet/intel/ice/ice_flow.c
>>>>> @@ -1573,12 +1573,13 @@ ice_flow_set_parser_prof(struct ice_hw *hw, u16 dest_vsi, u16 fdir_vsi,
>>>>>  			 struct ice_parser_profile *prof, enum ice_block blk)
>>>>>  {
>>>>>  	u64 id = find_first_bit(prof->ptypes, ICE_FLOW_PTYPE_MAX);
>>>>> -	struct ice_flow_prof_params *params __free(kfree);
>>>>>  	u8 fv_words = hw->blk[blk].es.fvw;
>>>>>  	int status;
>>>>>  	int i, idx;
>>>>>  
>>>>> -	params = kzalloc(sizeof(*params), GFP_KERNEL);
>>>>> +	struct ice_flow_prof_params *params __free(kfree) =
>>>>> +		kzalloc(sizeof(*params), GFP_KERNEL);
>>>>
>>>> Please don't do it that way. It's not C++ with RAII and
>>>> declare-where-you-use.
>>>> Just leave the variable declarations where they are, but initialize them
>>>> with `= NULL`.
>>>>
>>>> Variable declarations must be in one block and sorted from the longest
>>>> to the shortest.
>>>>
>>>
>>> These days, with __free the trend is to say yes this is RAII and we
>>> should declare it where you use it.  I personally don't have a strong
>>
>> Sorta, but we can't "declare it where you use it" since we don't allow
>> declaration-after-statement in the kernel.
> 
> That changed when we merged cleanup.h.  It is allowed now.  I still don't
> like to declare variables anywhere unless it's a __free() variable and I
> think almost everyone else agrees.  The only subsystem which I know that
> completely moved to declaring variables willy-nilly was bcachefs.

Oops, seems like I completely missed that.
So does it mean we're now allowed to write code in C++ style:

int a = func_a();

func_b();

int c = func_c();

?

Anyway, I have the same preferences as you: to declare everything at the
top of the function (or the scope if it's a loop/if/whatever). And
didn't plan to change this :D

> 
> regards,
> dan carpenter

Thanks,
Olek