linux-kernel - Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu

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Message-ID: <20150915233818.GU4029@linux.vnet.ibm.com>
Date:	Tue, 15 Sep 2015 16:38:18 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org >> Linux Kernel Mailing List" 
	<linux-kernel@...r.kernel.org>, KVM list <kvm@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace
 signal_struct->group_rwsem with a global percpu_rwsem) causes regression for
 libvirt/kvm

On Tue, Sep 15, 2015 at 06:28:11PM -0400, Tejun Heo wrote:
> Hello,
> 
> On Tue, Sep 15, 2015 at 02:38:30PM -0700, Paul E. McKenney wrote:
> > I did take a shot at adding the rcu_sync stuff during this past merge
> > window, but it did not converge quickly enough to make it.  It looks
> > quite good for the next merge window.  There have been changes in most
> > of the relevant areas, so probably best to just try them and see which
> > works best.
> 
> Heh, I'm having a bit of trouble following.  Are you saying that the
> changes would be too big for -stable?  If so, I'll send out reverts of
> the culprit patches and then reapply them for this cycle so that it
> can land together with the rcu changes in the next merge window, but
> it'd be great to find out whether the rcu changes are enough for the
> issue that Christian is seeing to go away.  If not, I'll switch to a
> different locking scheme and mark those patches w/ stable tag.

Well, the decision as to what is too big for -stable is owned by the
-stable maintainers, not by me.

I am suggesting trying the options and seeing what works best, then
working to convince people as needed.

							Thanx, Paul

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