From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753335AbcALUTB (ORCPT ); Tue, 12 Jan 2016 15:19:01 -0500 Received: from casper.infradead.org ([85.118.1.10]:41660 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753306AbcALUS7 (ORCPT ); Tue, 12 Jan 2016 15:18:59 -0500 Date: Tue, 12 Jan 2016 21:18:56 +0100 From: Peter Zijlstra To: Sasha Levin Cc: Thomas Gleixner , LKML , Paul McKenney Subject: Re: timers: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected Message-ID: <20160112201856.GD6375@twins.programming.kicks-ass.net> References: <56955C0F.1090005@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56955C0F.1090005@oracle.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 On Tue, Jan 12, 2016 at 03:03:27PM -0500, Sasha Levin wrote: > [ 3408.703754] Call Trace: > [ 3408.733192] rcu_read_unlock_special (kernel/rcu/tree_plugin.h:503) > [ 3408.735155] __rcu_read_unlock (kernel/rcu/update.c:223) > [ 3408.736090] __lock_timer (include/linux/rcupdate.h:495 include/linux/rcupdate.h:930 kernel/time/posix-timers.c:709) I'm thinking this is one of those magic preemptible RCU bits.. --- kernel/time/posix-timers.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index 31d11ac9fa47..09e28733e725 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -701,17 +701,25 @@ static struct k_itimer *__lock_timer(timer_t timer_id, unsigned long *flags) if ((unsigned long long)timer_id > INT_MAX) return NULL; + /* + * One of the few rules of preemptible RCU is that one cannot do + * rcu_read_unlock() while holding a scheduler (or nested) lock when + * part of the read side critical section was irqs-enabled -- see + * rcu_read_unlock_special(). + */ + local_irq_safe(*flags); rcu_read_lock(); timr = posix_timer_by_id(timer_id); if (timr) { - spin_lock_irqsave(&timr->it_lock, *flags); + spin_lock(&timr->it_lock); if (timr->it_signal == current->signal) { rcu_read_unlock(); return timr; } - spin_unlock_irqrestore(&timr->it_lock, *flags); + spin_unlock(&timr->it_lock); } rcu_read_unlock(); + local_irq_restore(*flags); return NULL; }