From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754598AbbFBL7e (ORCPT ); Tue, 2 Jun 2015 07:59:34 -0400 Received: from mail-wg0-f45.google.com ([74.125.82.45]:33185 "EHLO mail-wg0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751949AbbFBL7Z (ORCPT ); Tue, 2 Jun 2015 07:59:25 -0400 Date: Tue, 2 Jun 2015 13:59:15 +0200 From: Ingo Molnar To: Gu Zheng Cc: Andy Lutomirski , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov , Thomas Gleixner , "linux-kernel@vger.kernel.org" , X86 ML Subject: Re: [RFC PATCH V2] x86, espfix: postpone the initialization of espfix stack for AP Message-ID: <20150602115915.GB20697@gmail.com> References: <20150514212753.GE29125@pd.tnic> <55551E07.8080509@zytor.com> <20150515065417.GB29973@gmail.com> <55559FDA.3010205@zytor.com> <555A40C9.6010605@kernel.org> <555B5105.4040808@zytor.com> <555F0139.9040404@cn.fujitsu.com> <55666D4A.5040006@cn.fujitsu.com> <556D7687.70402@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <556D7687.70402@cn.fujitsu.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 * Gu Zheng wrote: > The following lockdep warning occurrs when running with latest kernel: > [ 3.178000] ------------[ cut here ]------------ > [ 3.183000] WARNING: CPU: 128 PID: 0 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0xdd/0xe0() > [ 3.193000] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)) > [ 3.199000] Modules linked in: > > [ 3.203000] CPU: 128 PID: 0 Comm: swapper/128 Not tainted 4.1.0-rc3 #70 > [ 3.221000] 0000000000000000 2d6601fb3e6d4e4c ffff88086fd5fc38 ffffffff81773f0a > [ 3.230000] 0000000000000000 ffff88086fd5fc90 ffff88086fd5fc78 ffffffff8108c85a > [ 3.238000] ffff88086fd60000 0000000000000092 ffff88086fd60000 00000000000000d0 > [ 3.246000] Call Trace: > [ 3.249000] [] dump_stack+0x4c/0x65 > [ 3.255000] [] warn_slowpath_common+0x8a/0xc0 > [ 3.261000] [] warn_slowpath_fmt+0x55/0x70 > [ 3.268000] [] lockdep_trace_alloc+0xdd/0xe0 > [ 3.274000] [] __alloc_pages_nodemask+0xad/0xca0 > [ 3.281000] [] ? __lock_acquire+0xf6d/0x1560 > [ 3.288000] [] alloc_page_interleave+0x3a/0x90 > [ 3.295000] [] alloc_pages_current+0x17d/0x1a0 > [ 3.301000] [] ? __get_free_pages+0xe/0x50 > [ 3.308000] [] __get_free_pages+0xe/0x50 > [ 3.314000] [] init_espfix_ap+0x17b/0x320 > [ 3.320000] [] start_secondary+0xf1/0x1f0 > [ 3.327000] ---[ end trace 1b3327d9d6a1d62c ]--- > > This seems a mis-warning by lockdep, as we alloc pages with GFP_KERNEL in > init_espfix_ap() which is called before enabled local irq, and the lockdep > sub-system considers this behaviour as allocating memory with GFP_FS with local > irq disabled, then trigger the warning as mentioned about. Why should this be a 'mis-warning'? If the GFP_KERNEL allocation sleeps then we'll sleep with irqs disabled => bad. This looks like a real (albeit hard to trigger) bug. > Though we could allocate them on the boot CPU side and hand them over to the > secondary CPU, but it seemes a bit waste if some of cpus are offline. As thers > is no need to these pages(espfix stack) until we try to run user code, so we > postpone the initialization of espfix stack after cpu booted to avoid the noise. > -void init_espfix_ap(void) > +void init_espfix_ap(int cpu) > { So how about the concern I raised in a former thread, that the allocation should be done for the node the target CPU is on? The 'cpu' parameter should be propagated to the allocation as well, and turned into a node allocation or so. Even though some CPUs will share the espfix stack, some won't. Thanks, Ingo