From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934046AbbBDOQd (ORCPT ); Wed, 4 Feb 2015 09:16:33 -0500 Received: from mailout2.w1.samsung.com ([210.118.77.12]:30116 "EHLO mailout2.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933746AbbBDOQb (ORCPT ); Wed, 4 Feb 2015 09:16:31 -0500 MIME-version: 1.0 Content-type: text/plain; charset=UTF-8 X-AuditID: cbfec7f5-b7fc86d0000066b7-43-54d2292aa278 Content-transfer-encoding: 8BIT Message-id: <1423059387.24415.2.camel@AMDC1943> Subject: Re: [rcu] [ INFO: suspicious RCU usage. ] From: Krzysztof Kozlowski To: paulmck@linux.vnet.ibm.com Cc: Russell King - ARM Linux , Fengguang Wu , LKP , linux-kernel@vger.kernel.org, Bartlomiej Zolnierkiewicz , linux-arm-kernel@lists.infradead.org, Arnd Bergmann , MarkRutland Date: Wed, 04 Feb 2015 15:16:27 +0100 In-reply-to: <20150204131420.GC5370@linux.vnet.ibm.com> References: <20150201025922.GA16820@wfg-t540p.sh.intel.com> <1422957702.17540.1.camel@AMDC1943> <20150203162704.GR19109@linux.vnet.ibm.com> <1423049947.19547.6.camel@AMDC1943> <20150204130018.GG8656@n2100.arm.linux.org.uk> <20150204131420.GC5370@linux.vnet.ibm.com> X-Mailer: Evolution 3.10.4-0ubuntu2 X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFrrGLMWRmVeSWpSXmKPExsVy+t/xK7pampdCDCZM07T4O+kYu8XGGetZ Ld4/X89ssenxNVaLy7vmsFncvsxrsfJ4O6vF0usXmSzebv7O6sDpcX8vu8eaeWsYPVqae9g8 fv+axOixeM9LJo8HhzazeGxeUu/Rt2UVo8fnTXIBnFFcNimpOZllqUX6dglcGctXahbc5a7Y /babuYGxn7OLkZNDQsBEoufXHDYIW0ziwr31QDYXh5DAUkaJPY/3sIIkeAUEJX5MvsfSxcjB wSwgL3HkUjZImFlAXWLSvEXMEPWfGSXOrNvBBFGvL3F/2UNGEFtYwEhi5bupYHE2AWOJzcuX sIHMERGQk1gzMQmkl1lgK5PEhuu7wI5gEVCVuPnvLQuIzSlgLnF+7m2oBZOZJE4u+88E0iwh oCzR2O82gVFgFpLzZiGcNwvJeQsYmVcxiqaWJhcUJ6XnGukVJ+YWl+al6yXn525ihMTF1x2M S49ZHWIU4GBU4uHt6L0YIsSaWFZcmXuIUYKDWUmEd6vypRAh3pTEyqrUovz4otKc1OJDjEwc nFINjJw5rDodWjff3Xa6Jyhs5KT+JKj5dlNN4PqHGt9L96pyesy0zbP19tlkLT5z/x++64em Omholm5bdOvUbLNkbXYuuce9iROvxDI6L13J9mTmzOLfH88uVj7p/ynqjlOj3eUFk/asPhcf I+Be8MfwUU/UaU6Jzru5riuuLl8ioBW1e3brOnHVMCWW4oxEQy3mouJEAJjoENRpAgAA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On śro, 2015-02-04 at 05:14 -0800, Paul E. McKenney wrote: > On Wed, Feb 04, 2015 at 01:00:18PM +0000, Russell King - ARM Linux wrote: > > On Wed, Feb 04, 2015 at 12:39:07PM +0100, Krzysztof Kozlowski wrote: > > > +Cc some ARM people > > > > I wish that people would CC this list with problems seen on ARM. I'm > > minded to just ignore this message because of this in the hope that by > > doing so, people will learn something... > > > > > > Another thing I could do would be to have an arch-specific Kconfig > > > > variable that made ARM responsible for informing RCU that the CPU > > > > was departing, which would allow a call to as follows to be placed > > > > immediately after the complete(): > > > > > > > > rcu_cpu_notify(NULL, CPU_DYING_IDLE, (void *)(long)smp_processor_id()); > > > > > > > > Note: This absolutely requires that the rcu_cpu_notify() -always- > > > > be allowed to execute!!! This will not work if there is -any- possibility > > > > of __cpu_die() powering off the outgoing CPU before the call to > > > > rcu_cpu_notify() returns. > > > > Exactly, so that's not going to be possible. The completion at that > > point marks the point at which power _could_ be removed from the CPU > > going down. > > OK, sounds like a polling loop is required. I thought about using wait_on_bit() in __cpu_die() (the waiting thread) and clearing the bit on CPU being powered down. What do you think about such idea? Best regards, Krzysztof