linux-kernel - Re: [PATCH v3 2.6.39-rc1-tip 15/26] 15: uprobes: Handing int3 and singlestep exception.

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Date:	Thu, 21 Apr 2011 19:41:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 2.6.39-rc1-tip 15/26] 15: uprobes: Handing int3 and
 singlestep exception.

On Thu, 2011-04-21 at 22:40 +0530, Srikar Dronamraju wrote:
> * Peter Zijlstra <peterz@...radead.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.



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