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=-6.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,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 A8415C43381 for ; Fri, 22 Mar 2019 12:27:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 78E2320685 for ; Fri, 22 Mar 2019 12:27:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553257672; bh=5vlIzUe1terjkQX+7PJwOvk8Li/L2QgptU7GQAaA6GA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ZIRccq8iim4qNNQH76EDzsdWDPwp1/JgS/xOcYFj3Uyrt6ZcYP3yJX0DGLBIjWDoV HBIVY4uanS0id/G6fOd0L4vO67/Q9kmQyn8H1MGLk8Qp2nKoT3ija9CaTWf1G+YwJM 2fl7pD0oMS84as2xT2CrhstLCc+BgFPyd80ln8m4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731482AbfCVM1p (ORCPT ); Fri, 22 Mar 2019 08:27:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:38896 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2403758AbfCVM1Y (ORCPT ); Fri, 22 Mar 2019 08:27:24 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0F2C62054F; Fri, 22 Mar 2019 12:27:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553257643; bh=5vlIzUe1terjkQX+7PJwOvk8Li/L2QgptU7GQAaA6GA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=R2Vu95+aRu1XbS+7n22+u3Bo7uTbAA33Gqje63fyy/DOlmf4toSzq5UpTJiBlH8IU /Fn34V3/GwkFFoLlmzb+TUacBpy11W9TX5BujuXdszfVcsqwoSJpjvqs2SExXJCl0v FC6bNB6OE5nXuww0goF+dqA8UN9cLLuSq96a2sFA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "He, Bo" , "Zhang, Jun" , "Paul E. McKenney" , "xiao, jin" , Jie A Subject: [PATCH 4.9 113/118] rcu: Do RCU GP kthread self-wakeup from softirq and interrupt Date: Fri, 22 Mar 2019 12:16:25 +0100 Message-Id: <20190322111224.272969383@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190322111215.873964544@linuxfoundation.org> References: <20190322111215.873964544@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Zhang, Jun commit 1d1f898df6586c5ea9aeaf349f13089c6fa37903 upstream. The rcu_gp_kthread_wake() function is invoked when it might be necessary to wake the RCU grace-period kthread. Because self-wakeups are normally a useless waste of CPU cycles, if rcu_gp_kthread_wake() is invoked from this kthread, it naturally refuses to do the wakeup. Unfortunately, natural though it might be, this heuristic fails when rcu_gp_kthread_wake() is invoked from an interrupt or softirq handler that interrupted the grace-period kthread just after the final check of the wait-event condition but just before the schedule() call. In this case, a wakeup is required, even though the call to rcu_gp_kthread_wake() is within the RCU grace-period kthread's context. Failing to provide this wakeup can result in grace periods failing to start, which in turn results in out-of-memory conditions. This race window is quite narrow, but it actually did happen during real testing. It would of course need to be fixed even if it was strictly theoretical in nature. This patch does not Cc stable because it does not apply cleanly to earlier kernel versions. Fixes: 48a7639ce80c ("rcu: Make callers awaken grace-period kthread") Reported-by: "He, Bo" Co-developed-by: "Zhang, Jun" Co-developed-by: "He, Bo" Co-developed-by: "xiao, jin" Co-developed-by: Bai, Jie A Signed-off: "Zhang, Jun" Signed-off: "He, Bo" Signed-off: "xiao, jin" Signed-off: Bai, Jie A Signed-off-by: "Zhang, Jun" [ paulmck: Switch from !in_softirq() to "!in_interrupt() && !in_serving_softirq() to avoid redundant wakeups and to also handle the interrupt-handler scenario as well as the softirq-handler scenario that actually occurred in testing. ] Signed-off-by: Paul E. McKenney Link: https://lkml.kernel.org/r/CD6925E8781EFD4D8E11882D20FC406D52A11F61@SHSMSX104.ccr.corp.intel.com Signed-off-by: Greg Kroah-Hartman --- kernel/rcu/tree.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1718,15 +1718,23 @@ static int rcu_future_gp_cleanup(struct } /* - * Awaken the grace-period kthread for the specified flavor of RCU. - * Don't do a self-awaken, and don't bother awakening when there is - * nothing for the grace-period kthread to do (as in several CPUs - * raced to awaken, and we lost), and finally don't try to awaken - * a kthread that has not yet been created. + * Awaken the grace-period kthread. Don't do a self-awaken (unless in + * an interrupt or softirq handler), and don't bother awakening when there + * is nothing for the grace-period kthread to do (as in several CPUs raced + * to awaken, and we lost), and finally don't try to awaken a kthread that + * has not yet been created. If all those checks are passed, track some + * debug information and awaken. + * + * So why do the self-wakeup when in an interrupt or softirq handler + * in the grace-period kthread's context? Because the kthread might have + * been interrupted just as it was going to sleep, and just after the final + * pre-sleep check of the awaken condition. In this case, a wakeup really + * is required, and is therefore supplied. */ static void rcu_gp_kthread_wake(struct rcu_state *rsp) { - if (current == rsp->gp_kthread || + if ((current == rsp->gp_kthread && + !in_interrupt() && !in_serving_softirq()) || !READ_ONCE(rsp->gp_flags) || !rsp->gp_kthread) return;