linux-kernel - Re: [PATCH 1/5] ptrace: Prepare to fix racy accesses on task breakpoints

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Date:	Wed, 13 Apr 2011 17:10:44 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Will Deacon <will.deacon@....com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Prasad <prasad@...ux.vnet.ibm.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"v2.6.33.." <stable@...nel.org>
Subject: Re: [PATCH 1/5] ptrace: Prepare to fix racy accesses on task
 breakpoints

On Wed, Apr 13, 2011 at 03:34:18PM +0100, Will Deacon wrote:
> > Returning -ERSCH there would mean that the task struct doesn't exist,
> > or something confusing like this. Which is not true: the task exists.
> 
> Sure, we need a way of saying `you can't take a reference to the
> breakpoints for this task' without specifying why. So I guess -ESRCH is
> wrong but I don't know that -1 is correct either (then again, I'm not
> *too* bothered by it :).

-EBUSY perhaps? Well I took -1 by default...

> 
> > OTOH, the caller, which is ptrace, needs to take a decision when he
> > can't take a reference to the breakpoints. The behaviour is
> > to act as if the process does not exist anymore, which is about to
> > happen for real but we anticipate because the task has reached a
> > state in its exiting path where we can't manipulate the breakpoints
> > anymore.
> > 
> > So the rationale behind it is that -ERSCH is an interpretation
> > of the caller.
> > 
> > Right?
> 
> Yup.
> 
> For this and the ARM patch:
> 
> Acked-by: Will Deacon <will.deacon@....com>

Great! Thanks!
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