netdev - Re: [Intel-wired-lan] [PATCH 1/2] e1000e: Don't return uninitialized stats

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Date:   Tue, 25 Apr 2017 10:54:33 -0700
From:   Benjamin Poirier <bpoirier@...e.com>
To:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:     "Brown, Aaron F" <aaron.f.brown@...el.com>,
        "Neftin, Sasha" <sasha.neftin@...el.com>,
        David S Miller <davem@...emloft.net>,
        stephen@...workplumber.org,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        Stefan Priebe <s.priebe@...fihost.ag>
Subject: Re: [Intel-wired-lan] [PATCH 1/2] e1000e: Don't return uninitialized
 stats

On 2017/04/25 02:07, Jeff Kirsher wrote:
[...]
> > > 
> > > I don't see any memset in e1000e_get_stats64(). What kernel version
> > > are
> > > you looking at?
> > 
> > The call to memset was removed from the upstream kernel with:
> > -------------------------------------------------------------------
> > -----------------
> > commit 5944701df90d9577658e2354cc27c4ceaeca30fe
> > Author: stephen hemminger <stephen@...workplumber.org>
> > Date:   Fri Jan 6 19:12:53 2017 -0800
> > 
> >     net: remove useless memset's in drivers get_stats64
> > 
> >     In dev_get_stats() the statistic structure storage has already
> > been
> >     zeroed. Therefore network drivers do not need to call memset()
> > again.
> > ...
> > < changes to other drivers snipped out >
> > ...
> > diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c
> > b/drivers/net/ethernet/int
> > index 723025b..79651eb 100644
> > --- a/drivers/net/ethernet/intel/e1000e/netdev.c
> > +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
> > @@ -5925,7 +5925,6 @@ void e1000e_get_stats64(struct net_device
> > *netdev,
> >  {
> >         struct e1000_adapter *adapter = netdev_priv(netdev);
> > 
> > -       memset(stats, 0, sizeof(struct rtnl_link_stats64));
> >         spin_lock(&adapter->stats64_lock);
> >         e1000e_update_stats(adapter);
> >         /* Fill out the OS statistics structure */
> > -------------------------------------------------------------------
> > -----------------
> > 
> > This also is where the bad counters start to show up for e1000e for
> > my test systems.  From this driver on I see (very) large values for
> > tx_dropped, rx_over_errors and tx_fifo_errors on driver load (even
> > before bringing the interface up.  It seems the memset is not so
> > useless for this driver after all.  Would simply reverting the e1000e
> > portion of this patch resolve the issue?
> 
> Looks like Aaron beat me to the punch on pointing out that we had this
> very code in there before.  It appears that Stephen's
> assertion/assumption was incorrect about the stats structure being
> zero'd out, which is why we are seeing the issue.
> 
> I have no issue reverting Stephen's earlier patch, or do we want to
> pursue why the stats structure is not zero'd out and resolve that
> instead.  Either way, just want to make sure we are all on the same
> page as to the right solution so that we do not end up repeating this
> in the future.

If you revert the e1000e part of 5944701df90d ("net: remove useless
memset's in drivers get_stats64", v4.11-rc1) it will fix the issue with
ethtool but memset will be done twice for code paths that call
dev_get_stats() (sysfs, rtnl, ...). Not a big deal but this is not a
problem in the approach I initially suggested. Alternatively, we could
put a memset in e1000_get_ethtool_stats().

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