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Date: Mon, 30 Sep 2013 18:58:01 +0200
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [RFC] introduce synchronize_sched_{enter,exit}()
Message-ID: <20130930165801.GB25642@redhat.com>
References: <1378805550-29949-1-git-send-email-mgorman@suse.de> <1378805550-29949-38-git-send-email-mgorman@suse.de> <20130917143003.GA29354@twins.programming.kicks-ass.net> <20130929183634.GA15563@redhat.com> <20130930125942.GB12926@twins.programming.kicks-ass.net> <20130930142400.GK26785@twins.programming.kicks-ass.net> <20130930150653.GL26785@twins.programming.kicks-ass.net>
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>, Srikar Dronamraju <srikar@linux.vnet.ibm.com>, Ingo Molnar <mingo@kernel.org>, Andrea Arcangeli <aarcange@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, Paul McKenney <paulmck@linux.vnet.ibm.com>, Thomas Gleixner <tglx@linutronix.de>, Steven Rostedt <rostedt@goodmis.org>, Linus Torvalds <torvalds@linux-foundation.org>

On 09/30, Peter Zijlstra wrote:
>
> On Mon, Sep 30, 2013 at 04:24:00PM +0200, Peter Zijlstra wrote:
> > For that we'd have to decrement xxx->gp_count from cb_rcu_func(),
> > wouldn't we?
> >
> > Without that there's no guarantee the fast path readers will have a MB
> > to observe the write critical section, unless I'm completely missing
> > something obviuos here.
>
> Duh.. we should be looking at gp_state like Paul said.

Yes, yes, that is why we have xxx_is_idle(). Its name is confusing
even ignoring "xxx".

OK, I'll try to invent the naming (but I'd like to hear suggestions ;)
and send the patch. I am going to add "exclusive" and "rcu_domain/ops"
later, currently percpu_rw_semaphore needs ->rw_sem anyway.

Oleg.

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