Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757596Ab3HHBNI (ORCPT ); Wed, 7 Aug 2013 21:13:08 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:53656 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1757321Ab3HHBNG (ORCPT ); Wed, 7 Aug 2013 21:13:06 -0400 X-IronPort-AV: E=Sophos;i="4.89,836,1367942400"; d="scan'208";a="8148902" Message-ID: <5202F198.2060806@cn.fujitsu.com> Date: Thu, 08 Aug 2013 09:17:12 +0800 From: Lai Jiangshan User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc14 Thunderbird/3.1.4 MIME-Version: 1.0 To: Carsten Emde CC: paulmck@linux.vnet.ibm.com, Steven Rostedt , Peter Zijlstra , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/8] rcu: Ensure rcu read site is deadlock-immunity References: <1375871104-10688-1-git-send-email-laijs@cn.fujitsu.com> <20130807123827.GB4306@linux.vnet.ibm.com> <5202A003.7000903@osadl.org> In-Reply-To: <5202A003.7000903@osadl.org> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2013/08/08 09:11:39, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2013/08/08 09:11:40, Serialize complete at 2013/08/08 09:11:40 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2074 Lines: 47 On 08/08/2013 03:29 AM, Carsten Emde wrote: > Hi Paul, > >>> Although all articles declare that rcu read site is deadlock-immunity. >>> It is not true for rcu-preempt, it will be deadlock if rcu read site >>> overlaps with scheduler lock. >> >> The real rule is that if the scheduler does its outermost rcu_read_unlock() >> with one of those locks held, it has to have avoided enabling preemption >> through the entire RCU read-side critical section. >> >> That said, avoiding the need for this rule would be a good thing. >> >> How did you test this? The rcutorture tests will not exercise this. >> (Intentionally so, given that it can deadlock!) >> >>> ec433f0c, 10f39bb1 and 016a8d5b just partially solve it. But rcu read site >>> is still not deadlock-immunity. And the problem described in 016a8d5b >>> is still existed(rcu_read_unlock_special() calls wake_up). >>> >>> The problem is fixed in patch5. >> >> This is going to require some serious review and testing. One requirement >> is that RCU priority boosting not persist significantly beyond the >> re-enabling of interrupts associated with the irq-disabled lock. To do >> otherwise breaks RCU priority boosting. At first glance, the added >> set_need_resched() might handle this, but that is part of the review >> and testing required. >> >> Steven, would you and Carsten be willing to try this and see if it >> helps with the issues you are seeing in -rt? (My guess is "no", since >> a deadlock would block forever rather than waking up after a couple >> thousand seconds, but worth a try.) > Your guess was correct, applying this patch doesn't heal the NO_HZ_FULL+PREEMPT_RT_FULL 3.10.4 based system; it still is hanging at -> synchronize_rcu -> wait_rcu_gp. > > -Carsten. > I didn't find the problem you reported, could you give me a url? Thanx, Lai -- 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/