From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752247AbbIOV02 (ORCPT ); Tue, 15 Sep 2015 17:26:28 -0400 Received: from mail-yk0-f174.google.com ([209.85.160.174]:36669 "EHLO mail-yk0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751670AbbIOV00 (ORCPT ); Tue, 15 Sep 2015 17:26:26 -0400 Date: Tue, 15 Sep 2015 17:26:22 -0400 From: Tejun Heo To: Christian Borntraeger Cc: Paolo Bonzini , Peter Zijlstra , Ingo Molnar , "linux-kernel@vger.kernel.org >> Linux Kernel Mailing List" , KVM list , Oleg Nesterov , Paul McKenney Subject: Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem) causes regression for libvirt/kvm Message-ID: <20150915212622.GC495@htj.duckdns.org> References: <55F8097A.7000206@de.ibm.com> <20150915130550.GC16853@twins.programming.kicks-ass.net> <55F81EE2.4090708@de.ibm.com> <55F84A6B.1010207@redhat.com> <55F88991.7040406@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55F88991.7040406@de.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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