Re: [PATCH 5.10 038/146] mptcp: do not warn on bad input from the network

[Mat Martineau]

On Wed, 23 Jun 2021, Paolo Abeni wrote:

> Hello,
>
> On Wed, 2021-06-23 at 16:22 +0200, Pavel Machek wrote:
> > Hi!
> >
> > > From: Paolo Abeni <pabeni@xxxxxxxxxx>
> > >
> > > [ Upstream commit 61e710227e97172355d5f150d5c78c64175d9fb2 ]
> > >
> > > warn_bad_map() produces a kernel WARN on bad input coming
> > > from the network. Use pr_debug() to avoid spamming the system
> > > log.
> >
> > So... we switched from WARN _ONCE_ to pr_debug, as many times as we
> > detect the problem.
> >
> > Should this be pr_debug_once?
>
> Thank you for double checking this!
>
> In the MPTCP code, we use pr_debug() statements as a debug tool, e.g.
> when enabled, it could print per-packet info with no restriction.
>
> There are (a few) similar use in the plain TCP code.
>
> pr_debug() is not supposed to be enabled on any production system,
> while the WARN_ONCE could trigger automated tools for irrelevant
> network noise.
>
> I thing pr_debug() is fine here.

Hi Pavel -

I agree with Paolo. This is not a frequently encountered condition, even 
when turning on this specific pr_debug(). I'd say the previous use of the 
_ONCE() variant was mostly because the effects were not optional (not 
because of frequency).

For protocol development, pr_debug() is both off by default and more
useful when it _is_ enabled. I'd prefer to keep this patch as-is.

Thanks,


--
Mat Martineau
Intel