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=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 8921DC43381 for ; Fri, 15 Feb 2019 02:26:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 586912073D for ; Fri, 15 Feb 2019 02:26:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550197581; bh=9y6czDSPpA+bo3tP+Ec3orygXTuUceysrldRJ/qrXN8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ouZZZ5zOyIBlSVhwCRhoptdQjqFsTxDivryPBQZTykL5gDo/ECna/+9ocmOLaE33b xkDsKTmQZjXhGfnVEApENQ6jcl5blVJvoIon9q2J4C00FR0fzI5otril8hLDwjTOrn zUk8ucWjyjKtRR9QNrR0aDijA81o1gOSVmOl4Wh8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404957AbfBOCNy (ORCPT ); Thu, 14 Feb 2019 21:13:54 -0500 Received: from mail.kernel.org ([198.145.29.99]:53758 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404909AbfBOCNu (ORCPT ); Thu, 14 Feb 2019 21:13:50 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D406A206BA; Fri, 15 Feb 2019 02:13:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550196829; bh=9y6czDSPpA+bo3tP+Ec3orygXTuUceysrldRJ/qrXN8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YPILoM4+B3UV6d7Shd7w+9b1GtKII5vzxxgAz7qN7fHiF45bjTMN/NyqkBTi3SEoZ RNuHCs7DF/6bj9xjwyh532SbwImhfszg2z7jd4+WQtNy2mZdF8ZCmDWBZWxsvZ9rE4 vHiFYCoWczKhawsh8qTcswIMRWPmnaLoLJmHLgSo= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Prateek Sood , Peter Zijlstra , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL 4.14 19/40] sched/wait: Fix rcuwait_wake_up() ordering Date: Thu, 14 Feb 2019 21:12:52 -0500 Message-Id: <20190215021313.178476-19-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190215021313.178476-1-sashal@kernel.org> References: <20190215021313.178476-1-sashal@kernel.org> MIME-Version: 1.0 X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Prateek Sood [ 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 3aa01b74c1e3..5523fb0c20c8 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -306,7 +306,7 @@ 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