linux-kernel - Re: [PATCH v4 3.0-rc2-tip 13/22] 13: uprobes: Handing int3 and singlestep exception.

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Message-ID: <1308227724.13240.58.camel@twins>
Date:	Thu, 16 Jun 2011 14:35:24 +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>,
	Andi Kleen <andi@...stfloor.org>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jonathan Corbet <corbet@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 3.0-rc2-tip 13/22] 13: uprobes: Handing int3 and
 singlestep exception.

On Thu, 2011-06-16 at 17:34 +0530, Srikar Dronamraju wrote:
> > > +
> > > +cleanup_ret:
> > > +       if (u) {
> > > +               down_read(&mm->mmap_sem);
> > > +               if (!set_orig_insn(current, u, probept, true))
> > 
> > we try to undo the probe? That doesn't make any sense. I thought you
> > meant to return to userspace, let it re-take the trap and try again
> > until you do manage to allocate the user resource.
> 
> I meant removing the probe itself
> https://lkml.org/lkml/2011/4/21/279
> 
> We could try reseting and retrying the trap. Just that we might end up
> looping under memory pressure.
> 
> > 
> > This behaviour makes probes totally unreliable under memory pressure. 
> 
> Under memory pressure we could be unreliable. 

But that is total crap, there's nothing worse than unreliable debug
tools.


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