From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753183AbZHXUQh (ORCPT ); Mon, 24 Aug 2009 16:16:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752591AbZHXUQg (ORCPT ); Mon, 24 Aug 2009 16:16:36 -0400 Received: from mga11.intel.com ([192.55.52.93]:12038 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752436AbZHXUQg (ORCPT ); Mon, 24 Aug 2009 16:16:36 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.44,267,1249282800"; d="scan'208";a="486930030" Subject: Re: [tip:x86/pat] generic-ipi: Allow cpus not yet online to call smp_call_function with irqs disabled From: Suresh Siddha Reply-To: Suresh Siddha To: Nick Piggin Cc: "linux-kernel@vger.kernel.org" , "mingo@redhat.com" , "hpa@zytor.com" , "tglx@linutronix.de" , "linux-tip-commits@vger.kernel.org" In-Reply-To: <20090824054026.GR25721@wotan.suse.de> References: <20090824054026.GR25721@wotan.suse.de> Content-Type: text/plain Organization: Intel Corp Date: Mon, 24 Aug 2009 13:15:43 -0700 Message-Id: <1251144943.2636.16.camel@sbs-t61> Mime-Version: 1.0 X-Mailer: Evolution 2.26.3 (2.26.3-1.fc11) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2009-08-23 at 22:40 -0700, Nick Piggin wrote: > On Fri, Aug 21, 2009 at 11:51:50PM +0000, Suresh B wrote: > > Commit-ID: 269c861baa2fe7c114c3bc7831292758d29eb336 > > Gitweb: http://git.kernel.org/tip/269c861baa2fe7c114c3bc7831292758d29eb336 > > Author: Suresh Siddha > > AuthorDate: Wed, 19 Aug 2009 18:05:35 -0700 > > Committer: H. Peter Anvin > > CommitDate: Fri, 21 Aug 2009 16:25:43 -0700 > > > > generic-ipi: Allow cpus not yet online to call smp_call_function with irqs disabled > > > > Because of deadlock possiblities smp_call_function() is not allowed to > > be called with interrupts disabled. Add an exception for the cpu not > > yet online, as no one else can send smp call function interrupt to this > > cpu that is not yet online and as such deadlock condition is not possible. > > > > Signed-off-by: Suresh Siddha > > Acked-by: Nick Piggin > > Signed-off-by: H. Peter Anvin > > I don't know if we should allow the use of smp_call_function here -- > only call_function_single. CPU hotplug code is required to set up > some call_function data and if the cpu is offline then it might not > be set up correctly. We are doing the required allocations in CPU_UP_PREPARE. So we should be okay for any smp_call_function usage. > Also, I would say that we should just restrict this to wait==1 case > because in that case the stack can trivially be used for data. In > the wait==0 case, it is more complex. In the current implementation > it should be OK (it uses per-cpu data), but we've used kmalloc > there in the past, which probably wouldn't work either. In future if we add any kmalloc, we already have checks in kmalloc() that can be easily caught. I would like to make this change as generic as possible. thanks, suresh