Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752974AbbGKK1Y (ORCPT ); Sat, 11 Jul 2015 06:27:24 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:33659 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751198AbbGKK1X (ORCPT ); Sat, 11 Jul 2015 06:27:23 -0400 Date: Sat, 11 Jul 2015 12:27:18 +0200 From: Ingo Molnar To: Peter Zijlstra Cc: Masami Hiramatsu , Ingo Molnar , linux-kernel , Waiman Long Subject: Re: [BUG][tip/master] kernel panic while locking selftest at qspinlock_paravirt.h:137! Message-ID: <20150711102718.GA28523@gmail.com> References: <559FAD5E.3080309@hitachi.com> <20150710130028.GI19282@twins.programming.kicks-ass.net> <20150710135746.GA13461@gmail.com> <20150710142824.GK19282@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150710142824.GK19282@twins.programming.kicks-ass.net> 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 Content-Length: 1690 Lines: 48 * Peter Zijlstra wrote: > On Fri, Jul 10, 2015 at 03:57:46PM +0200, Ingo Molnar wrote: > > * Peter Zijlstra wrote: > > > > Do we want to make double unlock non-fatal unconditionally? > > > > No, just don't BUG() out, don't crash the system - generate a warning? > > So that would be a yes.. > > Something like so then? Won't this generate a splat on that locking self > test then? And upset people? > > --- > kernel/locking/qspinlock_paravirt.h | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h > index 04ab18151cc8..286e8978a562 100644 > --- a/kernel/locking/qspinlock_paravirt.h > +++ b/kernel/locking/qspinlock_paravirt.h > @@ -133,8 +133,14 @@ static struct pv_node *pv_unhash(struct qspinlock *lock) > * This guarantees a limited lookup time and is itself guaranteed by > * having the lock owner do the unhash -- IFF the unlock sees the > * SLOW flag, there MUST be a hash entry. > + * > + * This can trigger due to double-unlock. In which case, return a > + * random pointer so that __pv_queued_spin_unlock() can dereference it > + * without crashing. > */ > - BUG(); > + WARN_ON_ONCE(true); > + > + return (struct pv_node *)this_cpu_ptr(&mcs_nodes[0]); Yeah, just please also use debug_locks_silent to make the self-test execute properly or so. Thanks, Ingo -- 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/