Re: [PATCH] net: ena: initialize dim_sample

[Tom Rix]

On 1/10/23 8:58 AM, Shay Agroskin wrote:
> Eric Dumazet <edumazet@xxxxxxxxxx> writes:
>
> > On Sun, Jan 8, 2023 at 3:38 PM Tom Rix <trix@xxxxxxxxxx> 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