netdev - Re: [PATCH] net: ena: initialize dim

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Date:   Wed, 11 Jan 2023 10:46:50 +0200
From:   Shay Agroskin <shayagr@...zon.com>
To:     Tom Rix <trix@...hat.com>
CC:     Eric Dumazet <edumazet@...gle.com>, <akiyano@...zon.com>,
        <darinzon@...zon.com>, <ndagan@...zon.com>, <saeedb@...zon.com>,
        <davem@...emloft.net>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <nathan@...nel.org>, <ndesaulniers@...gle.com>, <khalasa@...p.pl>,
        <wsa+renesas@...g-engineering.com>, <yuancan@...wei.com>,
        <tglx@...utronix.de>, <42.hyeyoo@...il.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <llvm@...ts.linux.dev>
Subject: Re: [PATCH] net: ena: initialize dim_sample


Tom Rix <trix@...hat.com> writes:

> On 1/10/23 8:58 AM, Shay Agroskin wrote:
>>
>> Eric Dumazet <edumazet@...gle.com> writes:
>>
>>> On Sun, Jan 8, 2023 at 3:38 PM Tom Rix <trix@...hat.com> 
>>> wrote:
>>>>
>>>> clang static analysis reports this problem
>>>> drivers/net/ethernet/amazon/ena/ena_netdev.c:1821:2: warning:
>>>> Passed-by-value struct
>>>>   argument contains uninitialized data (e.g., field: 
>>>> 'comp_ctr')
>>>> [core.CallAndMessage]
>>>>         net_dim(&ena_napi->dim, dim_sample);
>>>>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>
>>>> net_dim can call dim_calc_stats() which uses the comp_ctr 
>>>> element,
>>>> so it must be initialized.
>>>
>>> This seems to be a dim_update_sample() problem really, when 
>>> comp_ctr
>>> has been added...
>>>
>>> Your patch works, but we could avoid pre-initializing 
>>> dim_sample in
>>> all callers,
>>> then re-writing all but one field...
>>>
>>> diff --git a/include/linux/dim.h b/include/linux/dim.h
>>> index
>>> 6c5733981563eadf5f06c59c5dc97df961692b02..4604ced4517268ef8912cd8053ac8f4d2630f977
>>> 100644
>>> --- a/include/linux/dim.h
>>> +++ b/include/linux/dim.h
>>> @@ -254,6 +254,7 @@ dim_update_sample(u16 event_ctr, u64 
>>> packets, u64
>>> bytes, struct dim_sample *s)
>>>         s->pkt_ctr   = packets;
>>>         s->byte_ctr  = bytes;
>>>         s->event_ctr = event_ctr;
>>> +       s->comp_ctr  = 0;
>>>  }
>>>
>>>  /**
>>
>> Hi,
>>
>> I'd rather go with Eric's solution to this issue than zero the 
>> whole
>> struct in ENA
>
> Please look at the other callers of dim_update_sample.  The 
> common
> pattern is to initialize the struct.
>
> This alternative will work, but the pattern of initializing the 
> struct
> the other (~20) callers should be refactored.
>
> Tom
>

While Eric's patch might be bigger if you also remove the 
pre-initialization in the other drivers, the Linux code itself 
would be smaller (granted not significantly) and
it make less room for pitfalls in adding DIM support in other 
drivers.

Is there a good argument against using Eric's patch other than 
'the other patch would be bigger' ?

Shay

>>
>> Thanks,
>> Shay
>>