linux-kernel - Re: [RFC][PATCH] HWPOISON: only early kill processes who installed SIGBUS handler

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Date:	Wed, 17 Jun 2009 10:04:04 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Mel Gorman <mel@....ul.ie>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	"riel@...hat.com" <riel@...hat.com>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [RFC][PATCH] HWPOISON: only early kill processes who installed SIGBUS handler

On Wed, Jun 17, 2009 at 02:37:02PM +0800, Wu Fengguang wrote:
> On Mon, Jun 15, 2009 at 10:22:25PM +0800, Wu Fengguang wrote:
> > On Mon, Jun 15, 2009 at 08:25:28PM +0800, Nick Piggin wrote:
> > > On Mon, Jun 15, 2009 at 08:10:01PM +0800, Wu Fengguang wrote:
> > > > On Mon, Jun 15, 2009 at 03:19:07PM +0800, Nick Piggin wrote:
> > > > > > For KVM you need early kill, for the others it remains to be seen.
> > > > > 
> > > > > Right. It's almost like you need to do a per-process thing, and
> > > > > those that can handle things (such as the new SIGBUS or the new
> > > > > EIO) could get those, and others could be killed.
> > > > 
> > > > To send early SIGBUS kills to processes who has called
> > > > sigaction(SIGBUS, ...)?  KVM will sure do that. For other apps we
> > > > don't mind they can understand that signal at all.
> > > 
> > > For apps that hook into SIGBUS for some other means and
> > 
> > Yes I was referring to the sigaction(SIGBUS) apps, others will
> > be late killed anyway.
> > 
> > > do not understand the new type of SIGBUS signal? What about
> > > those?
> > 
> > We introduced two new SIGBUS codes:
> >         BUS_MCEERR_AO=5         for early kill
> >         BUS_MCEERR_AR=4         for late  kill
> > I'd assume a legacy application will handle them in the same way (both
> > are unexpected code to the application).
> > 
> > We don't care whether the application can be killed by BUS_MCEERR_AO
> > or BUS_MCEERR_AR depending on its SIGBUS handler implementation.
> > But (in the rare case) if the handler
> > - refused to die on BUS_MCEERR_AR, it may create a busy loop and
> >   flooding of SIGBUS signals, which is a bug of the application.
> >   BUS_MCEERR_AO is one time and won't lead to busy loops.
> > - does something that hurts itself (ie. data safety) on BUS_MCEERR_AO,
> >   it may well hurt the same way on BUS_MCEERR_AR. The latter one is
> >   unavoidable, so the application must be fixed anyway.
> 
> This patch materializes the automatically early kill idea.
> It aims to remove the vm.memory_failure_ealy_kill sysctl parameter.
> 
> This is mainly a policy change, please comment.

Well then you can still early-kill random apps that did not
want it, and you may still cause problems if its sigbus
handler does something nontrivial.

Can you use a prctl or something so it can expclitly
register interest in this?

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