From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0ABBC352AA for ; Tue, 1 Oct 2019 10:01:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 97DDC2133F for ; Tue, 1 Oct 2019 10:01:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 97DDC2133F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2CA178E0005; Tue, 1 Oct 2019 06:01:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 27A858E0001; Tue, 1 Oct 2019 06:01:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 190BD8E0005; Tue, 1 Oct 2019 06:01:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0247.hostedemail.com [216.40.44.247]) by kanga.kvack.org (Postfix) with ESMTP id E81DE8E0001 for ; Tue, 1 Oct 2019 06:01:53 -0400 (EDT) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 83397180AD802 for ; Tue, 1 Oct 2019 10:01:53 +0000 (UTC) X-FDA: 75994774506.30.9ADBA56 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin30.hostedemail.com (Postfix) with ESMTP id 37B40180B3AAE for ; Tue, 1 Oct 2019 10:01:43 +0000 (UTC) X-HE-Tag: stew86_eea57c63bd01 X-Filterd-Recvd-Size: 3588 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf10.hostedemail.com (Postfix) with ESMTP for ; Tue, 1 Oct 2019 10:01:42 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 516351000; Tue, 1 Oct 2019 03:01:41 -0700 (PDT) Received: from [10.1.194.37] (e113632-lin.cambridge.arm.com [10.1.194.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8273D3F739; Tue, 1 Oct 2019 03:01:39 -0700 (PDT) Subject: Re: [PATCH] sched: Avoid spurious lock dependencies To: Peter Zijlstra , Qian Cai Cc: akpm@linux-foundation.org, bigeasy@linutronix.de, tglx@linutronix.de, thgarnie@google.com, tytso@mit.edu, cl@linux.com, penberg@kernel.org, rientjes@google.com, mingo@redhat.com, will@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, keescook@chromium.org References: <1568392064-3052-1-git-send-email-cai@lca.pw> <20190925093153.GC4553@hirez.programming.kicks-ass.net> <1569424727.5576.221.camel@lca.pw> <20190925164527.GG4553@hirez.programming.kicks-ass.net> <1569500974.5576.234.camel@lca.pw> <20191001091837.GK4536@hirez.programming.kicks-ass.net> From: Valentin Schneider Message-ID: <8160833a-d01b-a942-5087-65831c9f96e9@arm.com> Date: Tue, 1 Oct 2019 11:01:38 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191001091837.GK4536@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 01/10/2019 10:18, Peter Zijlstra wrote: > On Thu, Sep 26, 2019 at 08:29:34AM -0400, Qian Cai wrote: > >> Oh, you were talking about took #3 while holding #2. Anyway, your patch is >> working fine so far. Care to post/merge it officially or do you want me to post >> it? > > Does the below adequately describe the situation? > > --- > Subject: sched: Avoid spurious lock dependencies > > While seemingly harmless, __sched_fork() does hrtimer_init(), which, > when DEBUG_OBJETS, can end up doing allocations. > > This then results in the following lock order: > > rq->lock > zone->lock.rlock > batched_entropy_u64.lock > > Which in turn causes deadlocks when we do wakeups while holding that > batched_entropy lock -- as the random code does. > > Solve this by moving __sched_fork() out from under rq->lock. This is > safe because nothing there relies on rq->lock, as also evident from the > other __sched_fork() callsite. > > Fixes: b7d5dc21072c ("random: add a spinlock_t to struct batched_entropy") > Signed-off-by: Peter Zijlstra (Intel) Funky dependency, but the change looks fine to me. Reviewed-by: Valentin Schneider > --- > kernel/sched/core.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 7880f4f64d0e..1832fc0fbec5 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6039,10 +6039,11 @@ void init_idle(struct task_struct *idle, int cpu) > struct rq *rq = cpu_rq(cpu); > unsigned long flags; > > + __sched_fork(0, idle); > + > raw_spin_lock_irqsave(&idle->pi_lock, flags); > raw_spin_lock(&rq->lock); > > - __sched_fork(0, idle); > idle->state = TASK_RUNNING; > idle->se.exec_start = sched_clock(); > idle->flags |= PF_IDLE; > >