From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752848AbdEPTG1 (ORCPT ); Tue, 16 May 2017 15:06:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:36628 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750847AbdEPTG0 (ORCPT ); Tue, 16 May 2017 15:06:26 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DF1C423984 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Tue, 16 May 2017 15:06:21 -0400 From: Steven Rostedt To: Thomas Gleixner Cc: LKML , Peter Zijlstra , Ingo Molnar , Mark Rutland , Greg Kroah-Hartman Subject: Re: [patch V2 01/17] init: Pin init task to boot cpu initially Message-ID: <20170516150621.548862a2@gandalf.local.home> In-Reply-To: <20170516184734.943149935@linutronix.de> References: <20170516184231.564888231@linutronix.de> <20170516184734.943149935@linutronix.de> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 16 May 2017 20:42:32 +0200 Thomas Gleixner wrote: > Some of the boot code in init_kernel_freeable() which runs before SMP > bringup assumes (rightfully) that it runs on the boot cpu and therefor can > use smp_processor_id() in preemptible context. > > That works so far because the smp_processor_id() check starts to be > effective after smp bringup. That's just wrong. Starting with SMP bringup > and the ability to move threads around, smp_processor_id() in preemptible > context is broken. > > Aside of that it does not make sense to allow init to run on all cpus > before sched_smp_init() has been run. > > Pin the init to the boot cpu so the existing code can continue to use > smp_processor_id() without triggering the checks when the enabling of those > checks starts earlier. > > Signed-off-by: Thomas Gleixner > --- > init/main.c | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > --- a/init/main.c > +++ b/init/main.c > @@ -389,6 +389,7 @@ static __initdata DECLARE_COMPLETION(kth > > static noinline void __ref rest_init(void) > { > + struct task_struct *tsk; > int pid; > > rcu_scheduler_starting(); > @@ -397,7 +398,17 @@ static noinline void __ref rest_init(voi > * the init task will end up wanting to create kthreads, which, if > * we schedule it before we create kthreadd, will OOPS. > */ > - kernel_thread(kernel_init, NULL, CLONE_FS); > + pid = kernel_thread(kernel_init, NULL, CLONE_FS); > + /* > + * Pin init on the boot cpu. Task migration is not properly working > + * until sched_init_smp() has been run. It will set the allowed > + * cpus for init to the non isolated cpus. > + */ > + rcu_read_lock(); > + tsk = find_task_by_pid_ns(pid, &init_pid_ns); Should we have a: BUG_ON(!tsk); Just to be paranoid? -- Steve > + set_cpus_allowed_ptr(tsk, cpumask_of(smp_processor_id())); > + rcu_read_unlock(); > + > numa_default_policy(); > pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); > rcu_read_lock(); > @@ -1015,10 +1026,6 @@ static noinline void __init kernel_init_ > * init can allocate pages on any node > */ > set_mems_allowed(node_states[N_MEMORY]); > - /* > - * init can run on any cpu. > - */ > - set_cpus_allowed_ptr(current, cpu_all_mask); > > cad_pid = task_pid(current); > >