linux-kernel - Re: [PATCH v5 3.1.0-rc4-tip 17/26] x86: arch specific hooks for pre/post singlestep handling.

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Date:	Tue, 27 Sep 2011 13:44:12 +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>,
	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>,
	Jonathan Corbet <corbet@....net>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	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 v5 3.1.0-rc4-tip 17/26]   x86: arch specific hooks for
 pre/post singlestep handling.

On Mon, 2011-09-26 at 22:04 +0530, Srikar Dronamraju wrote:
> * Peter Zijlstra <peterz@...radead.org> [2011-09-26 16:23:53]:
> 
> > On Tue, 2011-09-20 at 17:33 +0530, Srikar Dronamraju wrote:
> > > +fail:
> > > +       pr_warn_once("uprobes: Failed to adjust return address after"
> > > +               " single-stepping call instruction;"
> > > +               " pid=%d, sp=%#lx\n", current->pid, sp);
> > > +       return -EFAULT; 
> > 
> > So how can that happen? Single-Step while someone unmapped the stack?
> 
> We do a copy_to_user, copy_from_user just above this,

I saw that,

>  Now if either of
> them fail, we have no choice but to Bail out.

Agreed,

>  What caused this EFault may not be under Uprobes's Control.

I never said it was.. All I asked is what (outside of uprobe) was done
to cause this, and why is this particular error important enough to
warrant a warn.
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