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Subject: Re: [PATCH] net: ena: initialize dim_sample
To:     Shay Agroskin <shayagr@amazon.com>
Cc:     Eric Dumazet <edumazet@google.com>, 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>
 <db824c89-13f2-3349-9dd0-0fb7559c6273@redhat.com>
 <pj41zllem9bglr.fsf@u570694869fb251.ant.amazon.com>
From:   Tom Rix <trix@redhat.com>
Message-ID: <010f0cef-0f6e-1d4e-47ec-29a3c667b97a@redhat.com>
Date:   Wed, 11 Jan 2023 06:29:53 -0800
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On 1/11/23 12:46 AM, Shay Agroskin wrote:
>
> Tom Rix <trix@redhat.com> writes:
>
>> 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
>>
>
> 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' ?

No, I think it a better approach and if Eric can take it forward that 
would be great.

However when you start refactoring, it may grow larger than the single fix.

For instance, passing the structure by value could be changed to passing 
by reference.

Tom

>
> Shay
>
>>>
>>> Thanks,
>>> Shay
>>>
>