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

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Date:   Mon, 9 Jan 2023 11:34:28 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Tom Rix <trix@...hat.com>
Cc:     shayagr@...zon.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

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;
 }

 /**