linux-kernel - Re: [PATCH 12/X] uprobes: x86: introduce abort

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Date:	Fri, 21 Oct 2011 18:22:19 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, 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>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 12/X] uprobes: x86: introduce abort_xol()

On 10/21, Srikar Dronamraju wrote:
>
> > If it is not clear, abort_xol() is needed when we should
> > re-execute the original insn (replaced with int3), see the
> > next patch.
>
> We should be removing the breakpoint in abort_xol().

Why? See also below.

> Otherwise if we just set the instruction pointer to int3 and signal a
> sigill, then the user may be confused why a breakpoint is generating
> SIGILL.

Which user?

gdb? Of course it can be confused. But it can be confused in any case.

> > +void abort_xol(struct pt_regs *regs)
> > +{
> > +	// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> > +	// !!! Dear Srikar and Ananth, please implement me !!!
> > +	// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> > +	struct uprobe_task *utask = current->utask;
> > +	regs->ip = utask->vaddr;
>
> nit:
> Shouldnt we be setting the ip to the next instruction after this
> instruction?

Not sure...

We should restart the same insn. Say, if the probed insn
was "*(int*)0 = 0", it should be executed again after SIGSEGV. Unless
the task was killed by this signal.

And in this case we should call uprobe_consumer()->handler() again,
we shouldn't remove "int3".

> I have applied all your patches and ran tests, the tests are all
> passing.
>
> I will fold them into my patches and send them out.

Great, thanks.

Oleg.

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