linux-kernel - Re: [RFC] Make need_resched() return true when rcu_urgent

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Date:   Thu, 19 Jul 2018 10:09:53 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        Peter Zijlstra <peterz@...radead.org>, mhillenb@...zon.de,
        linux-kernel <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>
Subject: Re: [RFC] Make need_resched() return true when rcu_urgent_qs
 requested

On Wed, Jul 18, 2018 at 09:37:12AM -0700, Paul E. McKenney wrote:
> On Wed, Jul 18, 2018 at 06:01:51PM +0200, David Woodhouse wrote:
> > On Wed, 2018-07-18 at 08:36 -0700, Paul E. McKenney wrote:
> > > And I finally did get some near misses from an earlier commit, so we
> > > should consider your patch to be officially off the hook.
> > 
> > Yay, I like it when it's not my fault. I'll redo it with the ifdef
> > CONFIG_NO_HZ_FULL.
> 
> Hey, I didn't say it wasn't your fault, only that it -officially- wasn't
> your fault.  ;-)

And I believe that I found my bug in this commit (lots more testing still
required, but the preponderance of evidence and all that):

2cc0c7f07143 ("rcu: Eliminate ->rcu_qs_ctr from the rcu_dynticks structure")

So it really isn't your fault.

Of course, the real reason for the lack of fault on your part will not
because I believe I found the bug elsewhere, but instead because I will
be dropping your patch (and mine as well) on Frederic's advice.  ;-)

							Thanx, Paul