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=-9.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 12772C43381 for ; Mon, 4 Mar 2019 08:33:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D7AB1208E4 for ; Mon, 4 Mar 2019 08:33:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551688412; bh=YNDkFs0Yd6PxoY1PSzE5vIPGh62Bd9wq9CoyD8sBc+U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=d3d9nEtOW5jjz7JH8+FRv560Jq5pxtwrfAsbRW8H/TDYcgH/LCBIiAu79fK6w/0ch XmZbNbqkzK/clC0jl7/Nph47WCu7oWT46lbSEWpRhu86CRHsKM37izodI+j6XMnqtO P9bIb9QkXyvjO+QsZBlI/Yg24NNVybvRW3MkWDjs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727153AbfCDIda (ORCPT ); Mon, 4 Mar 2019 03:33:30 -0500 Received: from mail.kernel.org ([198.145.29.99]:38126 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727860AbfCDId2 (ORCPT ); Mon, 4 Mar 2019 03:33:28 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.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 C5C2C20823; Mon, 4 Mar 2019 08:33:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551688408; bh=YNDkFs0Yd6PxoY1PSzE5vIPGh62Bd9wq9CoyD8sBc+U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qmZJ7FU/r0tUx6VHnQduCHlu8hCBsRGMxlSrwkTufod+sQTTs364ZzqmNr5pEiF23 Apx/PCJ43KeFGdq0siF7I/STDsylxzd9EPEiGGCJAjgoD6TgChKYsSB9yw+429mXx8 Uxt2C0bGro7wRRYxFGs/jsdqZQy3l9RRr1/RcrgQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Prateek Sood , "Peter Zijlstra (Intel)" , Andrea Parri , Davidlohr Bueso , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH 4.20 35/88] sched/wait: Fix rcuwait_wake_up() ordering Date: Mon, 4 Mar 2019 09:22:18 +0100 Message-Id: <20190304081631.978000910@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190304081630.610632175@linuxfoundation.org> References: <20190304081630.610632175@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 4.20-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit 6dc080eeb2ba01973bfff0d79844d7a59e12542e ] For some peculiar reason rcuwait_wake_up() has the right barrier in the comment, but not in the code. This mistake has been observed to cause a deadlock in the following situation: P1 P2 percpu_up_read() percpu_down_write() rcu_sync_is_idle() // false rcu_sync_enter() ... __percpu_up_read() [S] ,- __this_cpu_dec(*sem->read_count) | smp_rmb(); [L] | task = rcu_dereference(w->task) // NULL | | [S] w->task = current | smp_mb(); | [L] readers_active_check() // fail `-> Where the smp_rmb() (obviously) fails to constrain the store. [ peterz: Added changelog. ] Signed-off-by: Prateek Sood Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Andrea Parri Acked-by: Davidlohr Bueso Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 8f95c90ceb54 ("sched/wait, RCU: Introduce rcuwait machinery") Link: https://lkml.kernel.org/r/1543590656-7157-1-git-send-email-prsood@codeaurora.org Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- kernel/exit.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/exit.c b/kernel/exit.c index 55b4fa6d01ebd..d607e23fd0c3e 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -307,7 +307,7 @@ void rcuwait_wake_up(struct rcuwait *w) * MB (A) MB (B) * [L] cond [L] tsk */ - smp_rmb(); /* (B) */ + smp_mb(); /* (B) */ /* * Avoid using task_rcu_dereference() magic as long as we are careful, -- 2.19.1