linux-kernel - Re: [PATCH] debug: Deprecate BUG_ON() use in new code, introduce CRASH

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Date:	Mon, 08 Jun 2015 11:22:03 +0200
From:	Alexander Holler <holler@...oftware.de>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Richard Weinberger <richard.weinberger@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tejun Heo <htejun@...il.com>,
	Louis Langholtz <lou_langholtz@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Trivial patch monkey <trivial@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] debug: Deprecate BUG_ON() use in new code, introduce
 CRASH_ON()

Am 08.06.2015 um 11:11 schrieb Ingo Molnar:
>
> * Ingo Molnar <mingo@...nel.org> wrote:
>
>> Firstly, the changelog of the patch that Greg rejected told nothing about all
>> that thinking, so at minimum it's a deficient changelog.
>>
>> Secondly and more importantly, instead of doing a BUG_ON() you could have done:
>>
>> 	if (WARN_ON_ONCE(port->itty))
>> 		return;
>>
>> This would probably have prevented the tty related memory corruption just as
>> much, at the cost of a (small and infrequent) memory leak.
>>
>> I.e. instead of crashing the machine, you need to try to find the least
>> destructive approach if a bug is detected.
>
> Also note that BUG_ON() will make data corruption _worse_ statistically. Why?
> Because most data corruptions are unlikely to be perfectly detected by a BUG_ON(),
> and the BUG_ON() delays the finding of the underlying bug, so the bug will hit
> more people before it's fixed for good.
>
> So even in the cases where you could argue that the system needs to stop, because
> we have evidence of data corruption, it's statistically the better approach to
> continue and get kernel log info back to developers.

Risking more, maybe even worse problems like corrupting file systems or 
similiar in order to have a slightly chance of save log info?

Sorry, that isn't something I would propose.

Anyway, CRASH_ON didn't exist, so I only had the choice between BUG_ON 
and WARN_ON, and for the latter you need a proper exit path which isn't 
always easy to find. So I appreciate CRASH_ON, thanks.

Alexander Holler
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