netdev - Re: dim_calc_stats() may cause uninitialized values to be used

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Message-ID: <YajhdLVPnuZkuKMU@unreal>
Date:   Thu, 2 Dec 2021 17:08:36 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Tony Battersby <tonyb@...ernetics.com>,
        Tal Gilboa <talgi@...dia.com>
Cc:     netdev@...r.kernel.org
Subject: Re: dim_calc_stats() may cause uninitialized values to be used

On Wed, Dec 01, 2021 at 02:40:47PM -0500, Tony Battersby wrote:
> I am reporting the following possible logic bug:
> 
> lib/dim/dim.c::dim_calc_stats() doesn't set curr_stats if delta_us == 0,
> which would result in using uninitialized values in net_dim_decision()
> and rdma_dim_decision().
> 
> I don't know anything about this code.  I encountered this only as a
> compiler warning compiling an out-of-tree module that had a copy of
> dim_calc_stats() inlined for compatibility with old kernels, and I
> decided to investigate and report.  There is no compiler warning in
> mainline since dim_calc_stats() and net_dim() are in separate C files so
> the compiler can't fully analyze it, but it looks like mainline has the
> problem also, if the delta_us == 0 condition is possible.

IMHO, it is false alarm, I don't see how delta_us can be 0. I would remove
this if (!delta_us) check.

Tal?

Thanks

> 
> Tony Battersby
> Cybernetics
>