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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_GIT autolearn=unavailable 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 47C6FCA9ECE for ; Thu, 31 Oct 2019 10:08:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 265582087F for ; Thu, 31 Oct 2019 10:08:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727332AbfJaKIg (ORCPT ); Thu, 31 Oct 2019 06:08:36 -0400 Received: from out4436.biz.mail.alibaba.com ([47.88.44.36]:6317 "EHLO out4436.biz.mail.alibaba.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726867AbfJaKIf (ORCPT ); Thu, 31 Oct 2019 06:08:35 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R231e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07486;MF=laijs@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0TgmBgR._1572516510; Received: from localhost(mailfrom:laijs@linux.alibaba.com fp:SMTPD_---0TgmBgR._1572516510) by smtp.aliyun-inc.com(127.0.0.1); Thu, 31 Oct 2019 18:08:30 +0800 From: Lai Jiangshan To: linux-kernel@vger.kernel.org Cc: Lai Jiangshan , "Paul E. McKenney" , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org Subject: [PATCH 02/11] rcu: fix bug when rcu_exp_handler() in nested interrupt Date: Thu, 31 Oct 2019 10:07:57 +0000 Message-Id: <20191031100806.1326-3-laijs@linux.alibaba.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191031100806.1326-1-laijs@linux.alibaba.com> References: <20191031100806.1326-1-laijs@linux.alibaba.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org These is a possible bug (although which I can't triger yet) since 2015 8203d6d0ee78 (rcu: Use single-stage IPI algorithm for RCU expedited grace period) rcu_read_unlock() ->rcu_read_lock_nesting = -RCU_NEST_BIAS; interrupt(); // before or after rcu_read_unlock_special() rcu_read_lock() fetch some rcu protected pointers // exp GP starts in other cpu. some works NESTED interrupt for rcu_exp_handler(); report exp qs! BUG! // exp GP completes and pointers are freed in other cpu some works with the pointers. BUG rcu_read_unlock(); ->rcu_read_lock_nesting = 0; Although rcu_sched_clock_irq() can be in nested interrupt, there is no such similar bug since special.b.need_qs can only be set when ->rcu_read_lock_nesting > 0 Signed-off-by: Lai Jiangshan --- kernel/rcu/tree_exp.h | 5 +++-- kernel/rcu/tree_plugin.h | 9 ++++++--- 2 files changed, 9 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 6dec21909b30..c0d06bce35ea 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -664,8 +664,9 @@ static void rcu_exp_handler(void *unused) * Otherwise, force a context switch after the CPU enables everything. */ rdp->exp_deferred_qs = true; - if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || - WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs())) { + if (rcu_preempt_need_deferred_qs(t) && + (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || + WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs()))) { rcu_preempt_deferred_qs(t); } else { set_tsk_need_resched(t); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index d4c482490589..59ef10da1e39 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -549,9 +549,12 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) */ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) { - return (__this_cpu_read(rcu_data.exp_deferred_qs) || - READ_ONCE(t->rcu_read_unlock_special.s)) && - t->rcu_read_lock_nesting <= 0; + return (__this_cpu_read(rcu_data.exp_deferred_qs) && + (!t->rcu_read_lock_nesting || + t->rcu_read_lock_nesting == -RCU_NEST_BIAS)) + || + (READ_ONCE(t->rcu_read_unlock_special.s) && + t->rcu_read_lock_nesting <= 0); } /* -- 2.20.1