Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752615AbbHaUc6 (ORCPT ); Mon, 31 Aug 2015 16:32:58 -0400 Received: from casper.infradead.org ([85.118.1.10]:42724 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752019AbbHaUc4 (ORCPT ); Mon, 31 Aug 2015 16:32:56 -0400 Date: Mon, 31 Aug 2015 22:32:50 +0200 From: Peter Zijlstra To: Alex Thorlton Cc: linux-kernel@vger.kernel.org, Ingo Molnar , John Stultz , Thomas Gleixner , Russ Anderson , Dimitri Sivanich Subject: Re: [BUG] Boot hangs at clocksource_done_booting on large configs Message-ID: <20150831203250.GH16853@twins.programming.kicks-ass.net> References: <20150831180432.GQ20615@asylum.americas.sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150831180432.GQ20615@asylum.americas.sgi.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1505 Lines: 48 On Mon, Aug 31, 2015 at 01:04:33PM -0500, Alex Thorlton wrote: q > diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c > index fd643d8..8502521 100644 > --- a/kernel/stop_machine.c > +++ b/kernel/stop_machine.c > @@ -417,8 +417,11 @@ static void cpu_stopper_thread(unsigned int cpu) > { > struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); > struct cpu_stop_work *work; > + unsigned long flags; > int ret; > > + local_irq_save(flags); > + > repeat: > work = NULL; > spin_lock_irq(&stopper->lock); > @@ -452,6 +455,8 @@ repeat: > cpu_stop_signal_done(done, true); > goto repeat; > } > + > + local_irq_restore(flags); > } > So I should probably just go sleep and not say anything.. _but_ *confused*. That local_irq_save() will disable IRQs over: work = NULL; But that is _all_. The spin_unlock_irq() will re-enable IRQs, after which things will run as usual. That local_irq_restore() is a total NOP, IRQs are guaranteed enabled at the irq_local_save() (otherwise lockdep would've complained about spin_unlock_irq() unconditionally enabling them) and by the time we get to the restore that same unlock_irq will have enabled them already. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/