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

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Date:	Thu, 16 Jun 2011 17:34:42 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
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.

> > +
> > +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.

> 
> > +                       atomic_dec(&mm->uprobes_count);
> > +               up_read(&mm->mmap_sem);
> > +               put_uprobe(u);
> > +       } else {
> > +       /*TODO Return SIGTRAP signal */
> > +       }
> > +       if (utask) {
> > +               utask->active_uprobe = NULL;
> > +               utask->state = UTASK_RUNNING;
> > +       }
> > +       set_instruction_pointer(regs, probept);
> > +} 
> 
> Also, there's a scary amount of TODO in there...

All of those deal with delaying the signals. I am working on it at this
moment. 

-- 
Thanks and Regards
Srikar
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