linux-kernel - Re: Q: perf_install_in_context/perf_event

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Date:	Mon, 31 Jan 2011 20:29:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
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 Mon, 2011-01-31 at 20:11 +0100, Oleg Nesterov wrote:
> 
> > > >   raw_spin_lock(&ctx->lock);
> > > > - ctx->is_active = 1;
> > > > + WARN_ON_ONCE(!ctx->is_active);
> > >
> > > This looks wrong if ctx->task == NULL.
> >
> > cpuctx->ctx should still have ->is_active = 1 I think.
> 
> Unless this is the first cpu counter, no? 

Ah, indeed.. 

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