linux-kernel - Re: [PATCH 04/10] x86: mce: fix error handling

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Date:	Sat, 31 Jul 2010 22:18:45 +0400
From:	Vasiliy Kulikov <segooon@...il.com>
To:	walter harms <wharms@....de>
Cc:	Andi Kleen <ak@...ux.intel.com>, kernel-janitors@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Borislav Petkov <borislav.petkov@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/10] x86: mce: fix error handling

On Thu, Jul 29, 2010 at 12:10 +0200, walter harms wrote:
> 
> 
> Andi Kleen schrieb:
> > 
> >> IMO memmory allocation fails are dangerous in kernel mode. As it is
> >> probably not exploitable because of boot time, it can destroy some
> >> sensitive data like dirty disk caches those are going to be written on
> >> disk.
> > 
> > It's true for runtime, but not for normal boot time.
> > 
> > Anyways if it happens on boot time the only thing you can do is panic,
> > but someone else
> > will likely panic anyways for you. Just ignoring it like your patch
> > effectively does
> > (because nothing will ever look at the ENOMEMs for an initcall) is wrong
> > though
> > In this case it's actually better to oops like the original code does.
> > 
> > BTW even with your patch likely later code will crash anyways because it
> > doesn't
> > expect init code to fail.
> > 
> 
> NTL it is nice to have a error message. for users it is worse if you crash suddenly
> with out warning than having a crash with "OOM" before because it gives you a clue
> what is going on.
> short:
> please think of users that are not kernel developers give them a hint what went wrong.
> 
> to make thinks more easy on boot we could replace kalloc() with kmalloc_or_die().
The thing is that this driver does not call kmalloc() explicitly, it
uses function those call functions those call kmalloc() :)

If we call BUG_ON() in init code, it would not make big overhead and
would make fault exactly when bug was detected, independent from caller
checks. Andi, are you fine with it?

> When anyone runs out of mem on boottime you can panic() instantly.
> 
> just my to cents,
>  wh
> 
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