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Date: Mon, 31 Jan 2011 20:11:09 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@elte.hu>,
        Alan Stern <stern@rowland.harvard.edu>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Paul Mackerras <paulus@samba.org>, Prasad <prasad@linux.vnet.ibm.com>,
        Roland McGrath <roland@redhat.com>, linux-kernel@vger.kernel.org
Subject: Re: Q: perf_install_in_context/perf_event_enable are racy?
Message-ID: <20110131191109.GA10906@redhat.com>
References: <1296134077.15234.161.camel@laptop> <20110127165712.GC25060@redhat.com> <1296148294.15234.242.camel@laptop> <20110127221856.GA10539@redhat.com> <1296215577.15234.333.camel@laptop> <1296226667.15234.337.camel@laptop> <20110128162847.GA25088@redhat.com> <1296238278.15234.340.camel@laptop> <20110131172626.GA5407@redhat.com> <1296498205.26581.54.camel@laptop>
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On 01/31, Peter Zijlstra wrote:
>
> On Mon, 2011-01-31 at 18:26 +0100, Oleg Nesterov wrote:
>
> > I do not understand the point of cpu_function_call() though, it looks
> > equal to smp_call_function_single() ?
>
> Very nearly so, except it takes a function that returns an int..

Ah, indeed...

> > >  	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?

Oleg.