From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <systemtap-return-17848-listarch-systemtap=sources.redhat.com@sourceware.org>
Received: (qmail 32581 invoked by alias); 21 Apr 2011 17:39:24 -0000
Received: (qmail 32251 invoked by uid 22791); 21 Apr 2011 17:39:21 -0000
X-SWARE-Spam-Status: No, hits=-3.0 required=5.0	tests=AWL,BAYES_00,TW_JL,T_RP_MATCHES_RCVD
X-Spam-Check-By: sourceware.org
Received: from casper.infradead.org (HELO casper.infradead.org) (85.118.1.10)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 21 Apr 2011 17:39:07 +0000
Received: from j77219.upc-j.chello.nl ([24.132.77.219] helo=dyad.programming.kicks-ass.net)	by casper.infradead.org with esmtpsa (Exim 4.72 #1 (Red Hat Linux))	id 1QCxqN-0008Uu-Ug	for systemtap@sources.redhat.com; Thu, 21 Apr 2011 17:39:08 +0000
Received: by dyad.programming.kicks-ass.net (Postfix, from userid 65534)	id B9D9F410B9EA; Thu, 21 Apr 2011 19:43:33 +0200 (CEST)
Received: from [IPv6:::1] (dyad [192.168.0.60])	by dyad.programming.kicks-ass.net (Postfix) with ESMTP id 4A94C404CC6C;	Thu, 21 Apr 2011 19:43:27 +0200 (CEST)
Subject: Re: [PATCH v3 2.6.39-rc1-tip 15/26] 15: uprobes: Handing int3 and singlestep exception.
From: Peter Zijlstra <peterz@infradead.org>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>, Linux-mm <linux-mm@kvack.org>, Arnaldo Carvalho de Melo <acme@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Jonathan Corbet <corbet@lwn.net>, Christoph Hellwig <hch@infradead.org>, Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,  Thomas Gleixner <tglx@linutronix.de>, Ananth N Mavinakayanahalli <ananth@in.ibm.com>, Oleg Nesterov <oleg@redhat.com>, LKML <linux-kernel@vger.kernel.org>, SystemTap <systemtap@sources.redhat.com>, Jim Keniston <jkenisto@linux.vnet.ibm.com>, Roland McGrath <roland@hack.frob.com>, Andi Kleen <andi@firstfloor.org>, Andrew Morton <akpm@linux-foundation.org>
In-Reply-To: <20110421171042.GI10698@linux.vnet.ibm.com>
References:	 <20110401143223.15455.19844.sendpatchset@localhost6.localdomain6>	 <20110401143527.15455.32854.sendpatchset@localhost6.localdomain6>	 <1303218185.8345.0.camel@twins> <20110421171042.GI10698@linux.vnet.ibm.com>
Content-Type: text/plain; charset="UTF-8"
Date: Thu, 21 Apr 2011 17:39:00 -0000
Message-ID: <1303407698.2035.159.camel@laptop>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm
Precedence: bulk
List-Id: <systemtap.sourceware.org>
List-Subscribe: <mailto:systemtap-subscribe@sourceware.org>
List-Post: <mailto:systemtap@sourceware.org>
List-Help: <mailto:systemtap-help@sourceware.org>, <http://sourceware.org/lists.html#faqs>
Sender: systemtap-owner@sourceware.org
X-SW-Source: 2011-q2/txt/msg00140.txt.bz2

On Thu, 2011-04-21 at 22:40 +0530, Srikar Dronamraju wrote:
> * Peter Zijlstra <peterz@infradead.org> [2011-04-19 15:03:05]:
> 
> > On Fri, 2011-04-01 at 20:05 +0530, Srikar Dronamraju wrote:
> > > +       if (unlikely(!utask)) {
> > > +               utask = add_utask();
> > > +
> > > +               /* Failed to allocate utask for the current task. */
> > > +               BUG_ON(!utask);
> > 
> > That's not really nice is it ;-) means I can make the kernel go BUG by
> > simply applying memory pressure.
> > 
> 
> The other option would be remove the probe and set the ip to
> the breakpoint address and restart the thread.

While its better than GFP_NOFAIL since its a return to userspace and
hence cannot be holding locks etc.. it's still not pretty. But heaps
better than simply bailing the kernel.