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

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Date:	Tue, 15 Sep 2015 17:26:22 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	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>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace
 signal_struct->group_rwsem with a global percpu_rwsem) causes regression for
 libvirt/kvm

Hello,

On Tue, Sep 15, 2015 at 11:11:45PM +0200, Christian Borntraeger wrote:
> > In fact, I would say that any userspace-controlled call to *_expedited()
> > is a bug waiting to happen and a bad idea---because userspace can, with
> > little effort, end up calling it in a loop.
> 
> Right. This also implies that we should fix this for 4.2 - I guess.

Are the percpu_rwsem changes enough?  If so, we can try to backport
those.  If those are too risky, we can revert the patches which
switched threadgroup lock to percpu_rwsem.

Thanks.

-- 
tejun
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