From: Joe Korty <joe.korty@ccur.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: "fweisbec@gmail.com" <fweisbec@gmail.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"laijs@cn.fujitsu.com" <laijs@cn.fujitsu.com>,
"mathieu.desnoyers@efficios.com" <mathieu.desnoyers@efficios.com>,
"dhowells@redhat.com" <dhowells@redhat.com>,
"loic.minier@linaro.org" <loic.minier@linaro.org>,
"dhaval.giani@gmail.com" <dhaval.giani@gmail.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"josh@joshtriplett.org" <josh@joshtriplett.org>,
"houston.jim@comcast.net" <houston.jim@comcast.net>,
"andi@firstfloor.org" <andi@firstfloor.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 8/9] jrcu: fix broken rcu_barrier
Date: Mon, 14 Mar 2011 18:09:28 -0400 [thread overview]
Message-ID: <20110314220928.GA1348@tsunami.ccur.com> (raw)
In-Reply-To: <20110314084718.GH2167@linux.vnet.ibm.com>
On Mon, Mar 14, 2011 at 04:47:18AM -0400, Paul E. McKenney wrote:
> On Sun, Mar 13, 2011 at 11:50:44PM -0400, Joe Korty wrote:
> > +void rcu_barrier(void)
> > +{
> > + synchronize_sched();
> > + synchronize_sched();
> > +}
>
> This is still broken. You need to wait until all pre-existing RCU
> callbacks on all CPUs have been invoked. Although this does guarantee
> that all callbacks on the current CPU have been invoked, if one of the
> other CPUs is busy, it might not yet have processed the callbacks from
> earlier grace periods. The usual way to take care of this is to post
> a callback on each CPU, then wait for them all to be invoked.
Hi Paul,
JRCU (eventually) chains together all callbacks from all
cpus into a single queue and then it expires that single
queue. So the double synchronize_sched() should work as
a rcu_barrier implementation.
Thanks,
Joe
next prev parent reply other threads:[~2011-03-14 22:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-14 3:50 [PATCH 8/9] jrcu: fix broken rcu_barrier Joe Korty
2011-03-14 8:47 ` Paul E. McKenney
2011-03-14 22:09 ` Joe Korty [this message]
2011-03-23 6:35 ` Paul E. McKenney
2011-03-23 13:46 ` Joe Korty
2011-03-24 0:23 ` Paul E. McKenney
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