From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756283Ab2D3QXE (ORCPT ); Mon, 30 Apr 2012 12:23:04 -0400 Received: from acsinet15.oracle.com ([141.146.126.227]:33209 "EHLO acsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754669Ab2D3QXC (ORCPT ); Mon, 30 Apr 2012 12:23:02 -0400 Date: Mon, 30 Apr 2012 12:17:16 -0400 From: Konrad Rzeszutek Wilk To: Greg KH Cc: linux-kernel@vger.kernel.org Subject: Re: udev races with 'arch_register_cpu' to write 1 to /sys/devices/system/cpu/cpu1/online (which is not yet created). Message-ID: <20120430161716.GA991@phenom.dumpdata.com> References: <20120430153623.GA23485@phenom.dumpdata.com> <20120430155018.GA16794@kroah.com> <20120430155149.GB16794@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120430155149.GB16794@kroah.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 30, 2012 at 11:51:49AM -0400, Greg KH wrote: > On Mon, Apr 30, 2012 at 11:50:18AM -0400, Greg KH wrote: > > On Mon, Apr 30, 2012 at 11:36:23AM -0400, Konrad Rzeszutek Wilk wrote: > > > Hey Greg, > > > > > > Hoping you can help with some guidance on how to fix this. > > > > > > The issue is with CPU hotplug is that when a CPU goes up > > > it calls 'arch_register_cpu' which eventually calls > > > register_cpu. That function does these two things: > > > > > > 251 error = device_register(&cpu->dev); > > > 252 if (!error && cpu->hotpluggable) > > > 253 register_cpu_control(cpu); > > > > > > and the device_register creates a nice little SysFS directory: > > > > > > /sys/devices/system/cpu/cpu2/ which at line 251 has the 'add' attribute > > > but no 'online' attribute. udev then tries to echo 1 to the 'online' > > > and it we get: > > > udevd-work[2421]: error opening ATTR{/sys/devices/system/cpu/cpu2/online} for writing: No such file or directory > > > > > > Line 253 creates said 'online' and at that time udev [or the system admin] > > > can write 1 to 'online' and the CPU goes up. > > > > > > So .. any thoughts? Is there some way to inhibit from uevent being sent > > > until line 253 has run? > > > > Yes. > > Oh, I imagine you want to know _how_ to do it too, right? (sorry, I > couldn't resist...) Heh. > > Make this a default attribute of the cpu device, and then it will be > created by the driver core before the uevent is sent to userspace. > That's what you are supposed to do in the first place, adding files "by > hand" is wrong, for this very reason. OK, will prep up a patch shortly.