From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id 70CD96B005C for ; Wed, 17 Jun 2009 07:55:04 -0400 (EDT) Date: Wed, 17 Jun 2009 19:56:34 +0800 From: Wu Fengguang Subject: Re: [RFC][PATCH] HWPOISON: only early kill processes who installed SIGBUS handler Message-ID: <20090617115634.GA5924@localhost> References: <20090615064447.GA18390@wotan.suse.de> <20090615070914.GC31969@one.firstfloor.org> <20090615071907.GA8665@wotan.suse.de> <20090615121001.GA10944@localhost> <20090615122528.GA13256@wotan.suse.de> <20090615142225.GA11167@localhost> <20090617063702.GA20922@localhost> <20090617080404.GB31192@wotan.suse.de> <20090617095532.GA25001@localhost> <20090617100006.GC14915@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090617100006.GC14915@wotan.suse.de> Sender: owner-linux-mm@kvack.org To: Nick Piggin Cc: Andi Kleen , Balbir Singh , Andrew Morton , LKML , Ingo Molnar , Mel Gorman , Thomas Gleixner , "H. Peter Anvin" , Peter Zijlstra , Hugh Dickins , "riel@redhat.com" , "chris.mason@oracle.com" , "linux-mm@kvack.org" List-ID: On Wed, Jun 17, 2009 at 06:00:06PM +0800, Nick Piggin wrote: > On Wed, Jun 17, 2009 at 05:55:32PM +0800, Wu Fengguang wrote: > > On Wed, Jun 17, 2009 at 04:04:04PM +0800, Nick Piggin wrote: > > > 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? > > > > No I don't think prctl would be much better. > > > > - if an application want early/late kill, it can do so with a proper > > written SIGBUS handler: the prctl call is redundant. > > s/proper written/is switched to new semantics based on the existance > of a/ Not necessarily so. If an application - did not has a SIGBUS handler, and want to be - early killed: must install a handler, this is not a big problem because it may well want to rescue something on the event. - late killed: just do nothing. (here kill = 'notification') - had a SIGBUS hander, and want to - early die: call exit(0) in the handler. - late die: intercept and ignore the signal. So if source code modification is viable, prctl is not necessary at all. > > - if an admin want to control early/late kill for an unmodified app, > > prctl is as unhelpful as this patch(*). > > Clearly you can execute a process with a given prctl. OK, right. > > - prctl does can help legacy apps whose SIGBUS handler has trouble > > with the new SIGBUS codes, however such application should be rare > > and the application should be fixed(why shall it do something wrong > > on newly introduced code at all? Shall we stop introducing new codes > > just because some random buggy app cannot handle new codes?) > > Backwards compatibility? Kind of important. Maybe. > > So I still prefer this patch, until we come up with some solution that > > allows both app and admin to change the setting. > > Not only does it allow that, but it also provides backwards > compatibility. Your patch does not allow admin to change > anything nor does it guarantee 100% back compat so I can't > see how you think it is better. I didn't say it is better, but clearly mean that prctl is not better enough to warrant a new user interface, if(!adm_friendly). Now it's obvious that adm_friendly=1, so I agree prctl is a good interface :) > Also it does not allow for an app with a SIGBUS handler to > use late kill. If late kill is useful to anyone, why would > it not be useful to some app with a SIGBUS handler (that is > not KVM)? Late kill will always be sent. Ignore the early kill signal in the SIGBUS handler does the trick (see above analyzes). Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org