linux-kernel - Re: [PATCH] net: ena: initialize dim

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Date:   Tue, 10 Jan 2023 18:58:37 +0200
From:   Shay Agroskin <shayagr@...zon.com>
To:     Eric Dumazet <edumazet@...gle.com>
CC:     Tom Rix <trix@...hat.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


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

Thanks,
Shay