From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753223AbbE1Bj4 (ORCPT ); Wed, 27 May 2015 21:39:56 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:64376 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751630AbbE1Bjs (ORCPT ); Wed, 27 May 2015 21:39:48 -0400 X-IronPort-AV: E=Sophos;i="5.01,1,1399996800"; d="scan'208";a="95967072" Message-ID: <55666D4A.5040006@cn.fujitsu.com> Date: Thu, 28 May 2015 09:20:10 +0800 From: Gu Zheng User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:7.0.1) Gecko/20110930 Thunderbird/7.0.1 MIME-Version: 1.0 To: "H. Peter Anvin" CC: Andy Lutomirski , Ingo Molnar , Borislav Petkov , Thomas Gleixner , , Subject: Re: [RFC PATCH] x86, espfix: postpone the initialization of espfix stack for AP References: <1431603465-12610-1-git-send-email-guz.fnst@cn.fujitsu.com> <20150514122621.GB29235@pd.tnic> <20150514182954.GB23479@gmail.com> <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> In-Reply-To: <555F0139.9040404@cn.fujitsu.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.100] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ping... On 05/22/2015 06:13 PM, Gu Zheng wrote: > The following lockdep warning occurs when running with 4.1.0-rc3: > [ 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. > > Though we could allocate them on the boot CPU side and hand them over to > the secondary CPU, but it seems a waste if some of cpus are still offline. > As there is no need to these pages(espfix stack) until we try to run user > code, so we can postpone the initialization of espfix stack after cpu > booted to avoid the noise. > > Signed-off-by: Gu Zheng > --- > arch/x86/kernel/smpboot.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > index 50e547e..3ce05de 100644 > --- a/arch/x86/kernel/smpboot.c > +++ b/arch/x86/kernel/smpboot.c > @@ -240,13 +240,6 @@ static void notrace start_secondary(void *unused) > check_tsc_sync_target(); > > /* > - * Enable the espfix hack for this CPU > - */ > -#ifdef CONFIG_X86_ESPFIX64 > - init_espfix_ap(); > -#endif > - > - /* > * We need to hold vector_lock so there the set of online cpus > * does not change while we are assigning vectors to cpus. Holding > * this lock ensures we don't half assign or remove an irq from a cpu. > @@ -901,6 +894,13 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) > } > } > > + /* > + * Enable the espfix hack for this CPU > + */ > +#ifdef CONFIG_X86_ESPFIX64 > + init_espfix_ap(); > +#endif > + > /* mark "stuck" area as not stuck */ > *trampoline_status = 0; >