From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [Xen-devel] [PATCH 05/27] xen, cpu hotplug: Don't call cpu_bringup() in xen_play_dead() Date: Fri, 01 Jun 2012 16:36:28 +0100 Message-ID: <4FC8FD9C0200007800087DF5@nat28.tlf.novell.com> References: <20120601090952.31979.24799.stgit@srivatsabhat.in.ibm.com> <20120601091124.31979.91984.stgit@srivatsabhat.in.ibm.com> <4FC8D8E30200007800087D2B@nat28.tlf.novell.com> <4FC8DC19.4000007@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Return-path: Received: from nat28.tlf.novell.com ([130.57.49.28]:42794 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759952Ab2FAPgf convert rfc822-to-8bit (ORCPT ); Fri, 1 Jun 2012 11:36:35 -0400 In-Reply-To: <4FC8DC19.4000007@linux.vnet.ibm.com> Content-Disposition: inline Sender: linux-arch-owner@vger.kernel.org List-ID: To: "Srivatsa S. Bhat" Cc: Russell King , yong.zhang0@gmail.com, Jeremy Fitzhardinge , peterz@infradead.org, mingo@kernel.org, x86@kernel.org, Thomas Gleixner , akpm@linux-foundation.org, nikunj@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com, vatsa@linux.vnet.ibm.com, virtualization@lists.linux-foundation.org, xen-devel@lists.xensource.com, Konrad Rzeszutek Wilk , Ingo Molnar , rusty@rustcorp.com.au, rjw@sisk.pl, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Keir Fraser , "H. Peter Anvin" >>> On 01.06.12 at 17:13, "Srivatsa S. Bhat" wrote: > On 06/01/2012 06:29 PM, Jan Beulich wrote: > >>>>> On 01.06.12 at 11:11, "Srivatsa S. Bhat" >> wrote: >>> xen_play_dead calls cpu_bringup() which looks weird, because xen_play_dead() >>> is invoked in the cpu down path, whereas cpu_bringup() (as the name >>> suggests) is useful in the cpu bringup path. >> >> This might not be correct - the code as it is without this change is >> safe even when the vCPU gets onlined back later by an external >> entity (e.g. the Xen tool stack), and it would in that case resume >> at the return point of the VCPUOP_down hypercall. That might >> be a heritage from the original XenoLinux tree though, and be >> meaningless in pv-ops context - Jeremy, Konrad? >> >> Possibly it was bogus/unused even in that original tree - Keir? >> > > > Thanks for your comments Jan! > > In case this change is wrong, the other method I had in mind was to call > cpu_bringup_and_idle() in xen_play_dead(). (Even ARM does something similar, > in the sense that it runs the cpu bringup code including cpu_idle(), in the > cpu offline path, namely the cpu_die() function). Would that approach work > for xen as well? If yes, then we wouldn't have any issues to convert xen to > generic code. No, that wouldn't work either afaict - the function is expected to return. Jan