linux-kernel - Re: Q: perf_install_in_context/perf_event

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Message-ID: <1296148294.15234.242.camel@laptop>
Date:	Thu, 27 Jan 2011 18:11:34 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Oleg Nesterov <oleg@...hat.com>
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 Thu, 2011-01-27 at 17:57 +0100, Oleg Nesterov wrote:
> 
> > With, however, things are more interesting. 2 seems to be adequately
> > covered by the patch I just send, the IPI will bail and the next
> > sched-in of the relevant task will pick matters up. 1 otoh doesn't seem
> > covered, the IPI will bail, leaving us stranded.
> 
> Hmm, yes... Strangely, I missed that when I was thinking about in_ctxsw.
> 
> Perhaps, we can change task_oncpu_function_call() so that it returns
> -EAGAIN in case it hits in_ctxsw != 0? If the caller sees -EAGAIN, it
> should always retry even if !ctx->is_active.

That would be very easy to do, we can pass a return value through the
task_function_call structure.
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