linux-kernel - Re: [PATCH] uprobes: don't enable/disable signle step if the user did it

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Date:	Mon, 30 Jul 2012 16:36:58 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] uprobes: don't enable/disable signle step if the user
	did it

On Thu, Jul 26, 2012 at 05:20:43PM +0200, Sebastian Andrzej Siewior wrote:
> If someone is using single stepping over uprobe brackpoint then after
> we pass the uprobe single step, single stepping is disabled and the user
> who enebaled them in the first place does not know anything about this.
> 
> This patch avoids enabling / disabling the single step mode if it is
> already enabled.

This could happen any time 2 different entities call the
user_(en/dis)able_single_step() helpers on the same thread.

Wouldn't the right way to fix it be to teach these helpers
to honor what the TIF_SINGLESTEP flag setting was in the first place?
This way you'd get rid of the portability concerns too, since these
helpers are available on most architectures.

Ananth

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