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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8120EC4332F for ; Sat, 24 Dec 2022 05:20:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230474AbiLXFU3 (ORCPT ); Sat, 24 Dec 2022 00:20:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57716 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229445AbiLXFUZ (ORCPT ); Sat, 24 Dec 2022 00:20:25 -0500 Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0B9C018687; Fri, 23 Dec 2022 21:20:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1671859223; x=1703395223; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=S40gLU/6WKa7SgaWDOJhy4OtsZ/xWarbNmOK4WXAaGM=; b=CYj+eaxdpW+hPgKNz9iOZbpXVS/xoukVd/yNt4TECJFh21hTKCgFZoir U/qX+vRD/kLSp1wPmaNMowPpaQjUk63D9q86PcnofOfe8EHReGOwZYmOp UxbSKS1ptxBqxI+tCzvxW93ms5skSDrYR4uyKBlaVEwFtAsmCq87WgV33 9iN4zW0/ppJraKZ/i62mDgQLbCfRGqxcaK7llKRkmstaggwcdZPJVbY6t 31F1XfvVraqmYZXdJU47fgvg8FUntiOcLeY5oAQO+G5NxgzIsXR7HU8yx 6fK1OUKahWTHYTS7NRLO6qn232e0yYs5jj42x8FdpttznrKRx2pSrCY08 w==; X-IronPort-AV: E=McAfee;i="6500,9779,10570"; a="320466535" X-IronPort-AV: E=Sophos;i="5.96,270,1665471600"; d="scan'208";a="320466535" Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Dec 2022 21:20:23 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10570"; a="826428622" X-IronPort-AV: E=Sophos;i="5.96,270,1665471600"; d="scan'208";a="826428622" Received: from zq-optiplex-7090.bj.intel.com ([10.238.156.129]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Dec 2022 21:20:21 -0800 From: Zqiang To: paulmck@kernel.org, frederic@kernel.org, quic_neeraju@quicinc.com, joel@joelfernandes.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] rcu: Safe access to rcu_node structure's->exp_tasks Date: Sat, 24 Dec 2022 13:25:53 +0800 Message-Id: <20221224052553.263199-1-qiang1.zhang@intel.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For kernels built with CONFIG_PREEMPT_RCU=y, the following scenario can result system oops. CPU1 CPU2 rcu_preempt_deferred_qs_irqrestore rcu_print_task_exp_stall if (special.b.blocked) READ_ONCE(rnp->exp_tasks) != NULL raw_spin_lock_rcu_node np = rcu_next_node_entry(t, rnp) if (&t->rcu_node_entry == rnp->exp_tasks) WRITE_ONCE(rnp->exp_tasks, np) .... raw_spin_unlock_irqrestore_rcu_node raw_spin_lock_irqsave_rcu_node t = list_entry(rnp->exp_tasks->prev, struct task_struct, rcu_node_entry) (if rnp->exp_tasks is NULL will trigger oops) This problem is that CPU2 accesses rcu_node structure's->exp_tasks without holding the rcu_node structure's ->lock and CPU2 did not observe CPU1's change to rcu_node structure's->exp_tasks in time, if rcu_node structure's->exp_tasks is set null pointer by CPU1, after that CPU2 accesses members of rcu_node structure's->exp_tasks will trigger oops. This commit therefore allows rcu_node structure's->exp_tasks to be accessed while holding rcu_node structure's ->lock. Signed-off-by: Zqiang --- kernel/rcu/tree_exp.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 7cc4856da081..902e7c8709c7 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -803,9 +803,11 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) int ndetected = 0; struct task_struct *t; - if (!READ_ONCE(rnp->exp_tasks)) - return 0; raw_spin_lock_irqsave_rcu_node(rnp, flags); + if (!READ_ONCE(rnp->exp_tasks)) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return 0; + } t = list_entry(rnp->exp_tasks->prev, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { -- 2.25.1