netdev - Re: bugs/regressions: report in LKML or in bugzilla?

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Date:	Tue, 7 Dec 2010 22:11:39 +0100
From:	Martin Steigerwald <Martin@...htvoll.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: bugs/regressions: report in LKML or in bugzilla?

Am Dienstag 07 Dezember 2010 schrieb Eric Dumazet:
> Le mardi 07 décembre 2010 à 16:39 +0100, Martin Steigerwald a écrit :
> > A participant of a linux performance training I hold found a bug with
> > window scaling which did not receive any reply as well:
> > 
> > Bug 20312 -  System freeze with multiples of 32 in
> > /proc/sys/net/ipv4/tcp_adv_win_scale
> > https://bugzilla.kernel.org/show_bug.cgi?id=20312
> 
> User bug ?

Sure, but whats the point?

> Documentation/networking/ip-sysctl.txt
> 
> tcp_adv_win_scale - INTEGER
> 	Count buffering overhead as bytes/2^tcp_adv_win_scale
> 	(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
> 	if it is <= 0.
> 	Default: 2
> 
> Given we use 32bit numbers, using values outside of [-31 ... 31] makes
> litle sense.

Granted, it does not make sense. The user tried that on an exercise to 
make TCP/IP networking in Linux as slow as possible (to understand why its 
fast at all).

Still: Here isn't documented that the kernel freezes when writing a wrong 
value in there.

> We could add sysctl range limit, but user should not mess with
> /proc/sys/net/ipv4/parameters unless he knows what he is doing ?
> 
> Almost all /proc/sys/net/ipv4/parameters dont have range limits and
> unexpected results with insane values feeded.

Well I disagree. Its a user interface, even tough a root user interface, 
that is even writable without writing a program. And as far as I 
understand even at least some system calls do some basic sanity checking 
on arguments.

If it doesn't cost too much overhead, arguments in there should receive at 
least some basic sanity checking.

> An other way to freeze a machine being root is :
> 
> halt

It won't freeze the machine. It does a clean halt which reduces the chance 
to reduce valuable data in yet unwritten pages.

And here it is documented that this will halt the machine.

Ciao,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
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