netdev - Re: [PATCH v6 net-next 11/15] net: catch errors from dev_get

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Date:   Mon, 18 Jan 2021 12:31:19 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Saeed Mahameed <saeed@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Eric Dumazet <edumazet@...gle.com>,
        George McCollister <george.mccollister@...il.com>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Arnd Bergmann <arnd@...db.de>, Taehee Yoo <ap420073@...il.com>,
        Jiri Pirko <jiri@...nulli.us>, Florian Westphal <fw@...len.de>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Pravin B Shelar <pshelar@....org>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>
Subject: Re: [PATCH v6 net-next 11/15] net: catch errors from dev_get_stats

On Mon, Jan 11, 2021 at 03:51:39PM -0800, Saeed Mahameed wrote:
> On Tue, 2021-01-12 at 01:15 +0200, Vladimir Oltean wrote:
> > On Mon, Jan 11, 2021 at 02:54:50PM -0800, Saeed Mahameed wrote:
> > > On Sat, 2021-01-09 at 19:26 +0200, Vladimir Oltean wrote:
> > > > From: Vladimir Oltean <vladimir.oltean@....com>
> > > >
> > > > dev_get_stats can now return error codes. Convert all remaining call
> > > > sites to look at that error code and stop processing.
> > > >
> > > > The effects of simulating a kernel error (returning -ENOMEM) upon
> > > > existing programs or kernel interfaces:
> > > >
> > > > - ifconfig and "cat /proc/net/dev" print up until the interface that
> > > >   failed, and there they return:
> > > > cat: read error: Cannot allocate memory
> > > >
> > > > - ifstat and "ip -s -s link show":
> > > > RTNETLINK answers: Cannot allocate memory
> > > > Dump terminated
> > > >
> > > > Some call sites are coming from a context that returns void (ethtool
> > > > stats, workqueue context). So since we can't report to the upper layer,
> > > > do the next best thing: print an error to the console.
> > > >
> > >
> > > another concern, one buggy netdev driver in a system will cause
> > > unnecessary global failures when reading stats via netlink/procfs
> > > for all the netdev in a netns, when other drivers will be happy to
> > > report.
> > >
> > > can't we just show a message in that driver's stats line about the
> > > occurred err ? and show the normal stats line of all others ?
> >
> > So you're worried that user space apps won't handle an error code when
> > reading from a file, but you're not worried that they'll start scraping
> > junk from procfs when we print this?
>
> both are equivalently concerning.
> to avoid any user crashes, we can just toss failed netdevs out from the
> output.

I'm not sure I'm on the same page here, basically I churned through the
whole kernel to propagate the error code from dev_get_stats, just to not
report it anywhere?