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Date: Fri, 6 Sep 2024 15:12:11 +0200
From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>,
	Z qiang <qiang.zhang1211@gmail.com>, rcu@vger.kernel.org
Subject: Re: One-off rcu_nocb_rdp_deoffload bug
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In-Reply-To: <3e62cd89-441f-4a9a-aff7-7ca1dda3c34d@paulmck-laptop>

Le Thu, Sep 05, 2024 at 11:04:22PM -0700, Paul E. McKenney a écrit :
> On Thu, Sep 05, 2024 at 08:41:02PM +0200, Frederic Weisbecker wrote:
> > Le Thu, Sep 05, 2024 at 08:32:16PM +0200, Frederic Weisbecker a écrit :
> > > Le Wed, Sep 04, 2024 at 06:52:36AM -0700, Paul E. McKenney a écrit :
> > > > > Yes, I'm preparing an update for the offending patch (which has one more
> > > > > embarassing issue while I'm going through it again).
> > > > 
> > > > Very good, thank you!
> > > 
> > > So my proposal for a replacement patch is this (to replace the patch
> > > of the same name in Neeraj tree):
> > 
> > FYI, the diffstat against the previous version of the same patch is as follows.
> > The rationale being:
> > 
> > 1) rdp->nocb_cb_kthread doesn't need to be protected by nocb_gp_kthread_mutex
> > 
> > 2) Once rcuoc is parked, we really _must_ observe the callback list counter decremented
> >    after the barrier's completion.
> > 
> > 3) This fixes another issue: rcuoc must be parked _before_
> >    rcu_nocb_queue_toggle_rdp() is called, otherwise a nocb locked sequence
> >    within rcuoc would race with rcuog clearing SEGCBLIST_OFFLOADED concurrently,
> >    leaving the nocb locked forever.
> 
> Thank you!!!
> 
> Just to make sure that I understand, I apply this patch on top of
> Neeraj's current set of branches to get the fix, correct?

Exactly!

Thanks.