linux-kernel - Re: [2/3] 2.6.22-rc2: known regressions v2

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Message-ID: <20070525101105.GA9268@elte.hu>
Date:	Fri, 25 May 2007 12:11:05 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Christoph Lameter <clameter@....com>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Cherwin R. Nooitmeer" <cherwin@...il.com>,
	linux-pcmcia@...ts.infradead.org,
	Robert de Rooy <robert.de.rooy@...il.com>,
	Alan Cox <alan@...hat.com>, Tejun Heo <htejun@...il.com>,
	sparclinux@...r.kernel.org, David Miller <davem@...emloft.net>,
	Mikael Pettersson <mikpe@...uu.se>,
	linux1394-devel@...ts.sourceforge.net,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Kristian H?gsberg <krh@...planet.net>,
	linux-pm@...ts.linux-foundation.org,
	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	Marcus Better <marcus@...ter.se>,
	Andrey Borzenkov <arvidjaar@...l.ru>,
	linux-usb-devel@...ts.sourceforge.net,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [2/3] 2.6.22-rc2: known regressions v2

* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> > i very much agree that this kmalloc_index() one shouldnt be called a 
> > "BUG: ", but if you look at the majority of WARN_ON() instances they 
> > are checks for clear, serious kernel bugs.
> 
> I _still_ disagree.
> 
> There's a huge difference between "You killed my father, prepare to 
> die", and "Btw, I didn't like that, but I'll just continue".

yeah ...

> And that's the difference between BUG_ON() and WARN_ON().

how about this solution: make WARN_ON() a "WARNING: " like you suggested 
(i still agree with that in principle), but also solve the additional 
problem i'm trying to outline: make BUG_ON() _not_ crash the box [only 
if the user asks for a crash to happen in such circumstances - this can 
be a sysctl.]. Then i can change the majority of the current WARN_ON()s 
to BUG_ON()s.

Most of the WARN_ON()s i personally add (and most of the WARN_ON()s i 
see others adding) are not WARN_ON()s because "i didnt like that and 
i'll just continue", they are WARN_ON() because i want _actual feedback 
from users_.

A BUG_ON() has a (much) lower likelyhood of being reported back - for 
most users it is a "X just hung hard, there was nothing in the syslog, i 
had to switch back to the older kernel" experience, and they do not have 
a serial console to hook up (newer hardware often doesnt even have a 
serial port). With the WARN_ON()s we have a _chance_ that despite the 
seriousness of the bug, the message makes it to the syslog, until the 
system comes to a screeching halt due to side-effects of the bug.

in that sense i am part of the problem: i was adding WARN_ON()s that 
werent true 'warnings' but 'bugs'. So i'd very much like to fix that 
problem, but i'd also like to solve the (very serious and existing) 
problem of BUG_ON()s making it less likely to get bugs reported back. 

	Ingo
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