linux-kernel - Re: Q: perf_install_in_context/perf_event

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Message-ID: <20110127155202.GA25060@redhat.com>
Date:	Thu, 27 Jan 2011 16:52:02 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Alan Stern <stern@...land.harvard.edu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Prasad <prasad@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Q: perf_install_in_context/perf_event_enable are racy?

On 01/27, Peter Zijlstra wrote:
>
> On Wed, 2011-01-26 at 22:33 +0100, Oleg Nesterov wrote:
> >
> > This is what I had in mind initially but I didn't dare to add the
> > new member into rq, it is only needed for perf.
>
> Right, but its a weakness in the task_oncpu_function_call()
> implementation, wouldn't any user run into this problem eventually?

I think that other users are fine, they do not try to change ctx.

OTOH, probably your change in task_oncpu_function_call() makes sense
anyway, this way func() can never have some other subtle problems
witht context_switch in progress.

Oleg.

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