linux-kernel - Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical section?

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Message-ID: <00000141128b3e55-996e72db-3257-4d38-801a-ab70a7a20ca2-000000@email.amazonses.com>
Date:	Thu, 12 Sep 2013 14:20:18 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Ingo Molnar <mingo@...nel.org>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...icios.com, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, sbw@....edu
Subject: Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical
 section?

On Thu, 12 Sep 2013, Ingo Molnar wrote:

>
> * Christoph Lameter <cl@...ux.com> wrote:
>
> > On Mon, 9 Sep 2013, Ingo Molnar wrote:
> >
> > > I saw those, he posted 'needs testing' patches. He still behaved
> > > passive-aggressively, pretending that it was some difficult task to
> > > perform, as if we were pulling his teeth.
> >
> > I need your review of those. I will rediff as soon as rc1 is out to send
> > something that can be put into -next. Please tell me until then if the
> > approach is ok. I dont think we can do anything in the merge window.
>
> The patch looked OK. Have you tested it, such as using a this_cpu op on a
> PREEMPT=y kernel in a preemptible section? That should trigger the preempt
> warning.

The reason that certain __this_cpu ops were converted to raw_cpu ops is
because they triggered the preemption check. The test was done in a kvm
environment (as evident from the description).



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