Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752075AbbGKGsC (ORCPT ); Sat, 11 Jul 2015 02:48:02 -0400 Received: from fallback.hitachi.co.jp ([133.145.228.49]:45082 "EHLO mailx.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750836AbbGKGr5 (ORCPT ); Sat, 11 Jul 2015 02:47:57 -0400 Message-ID: <55A06439.90002@hitachi.com> Date: Sat, 11 Jul 2015 09:32:57 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Peter Zijlstra , Ingo Molnar CC: Ingo Molnar , linux-kernel , Waiman Long Subject: Re: [BUG][tip/master] kernel panic while locking selftest at qspinlock_paravirt.h:137! References: <559FAD5E.3080309@hitachi.com> <20150710130028.GI19282@twins.programming.kicks-ass.net> <20150710135746.GA13461@gmail.com> <20150710142824.GK19282@twins.programming.kicks-ass.net> In-Reply-To: <20150710142824.GK19282@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2000 Lines: 57 On 2015/07/10 23:28, 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? Hmm, yes, this still noisy... Can't we avoid double-unlock completely? it seems that this warning can happen randomly, which means pv-spinlock randomly broken, doesn't it? Thank you, > --- > 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]); > } > > /* > -- Masami HIRAMATSU Linux Technology Research Center, System Productivity Research Dept. Center for Technology Innovation - Systems Engineering Hitachi, Ltd., Research & Development Group E-mail: masami.hiramatsu.pt@hitachi.com -- 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/