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Subject: Re: [PATCH] net: ena: initialize dim_sample
To:     Shay Agroskin <shayagr@amazon.com>,
        Eric Dumazet <edumazet@google.com>
Cc:     akiyano@amazon.com, darinzon@amazon.com, ndagan@amazon.com,
        saeedb@amazon.com, davem@davemloft.net, kuba@kernel.org,
        pabeni@redhat.com, nathan@kernel.org, ndesaulniers@google.com,
        khalasa@piap.pl, wsa+renesas@sang-engineering.com,
        yuancan@huawei.com, tglx@linutronix.de, 42.hyeyoo@gmail.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
References: <20230108143843.2987732-1-trix@redhat.com>
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 <pj41zlpmbmba16.fsf@u570694869fb251.ant.amazon.com>
From:   Tom Rix <trix@redhat.com>
Message-ID: <db824c89-13f2-3349-9dd0-0fb7559c6273@redhat.com>
Date:   Tue, 10 Jan 2023 09:17:56 -0800
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On 1/10/23 8:58 AM, Shay Agroskin wrote:
>
> Eric Dumazet <edumazet@google.com> writes:
>
>> On Sun, Jan 8, 2023 at 3:38 PM Tom Rix <trix@redhat.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

>
> Thanks,
> Shay
>