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=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 0E242C43381 for ; Mon, 4 Mar 2019 08:44:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D0BC22082F for ; Mon, 4 Mar 2019 08:44:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551689047; bh=3cF/Yiq5ee9rCDPnZdE60Sgu5RFuQnyZmb82eGccUd0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=I6H1rkm+B8/UDpXagNYs1buMniKjEBzlkV/vU9yklCgC7+khy7Zfj2k2W1lHwQco9 llDh2eSDS94BCDgHNxp+MqCQogyv1jUO2rknRBfWqqkN8DI5Qk0DefgAoGCQ39aZEC M4UsyeWXAQvIvVma43UKgJgn9x0PAggvJko7fd6M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726506AbfCDI3S (ORCPT ); Mon, 4 Mar 2019 03:29:18 -0500 Received: from mail.kernel.org ([198.145.29.99]:55564 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726724AbfCDI3Q (ORCPT ); Mon, 4 Mar 2019 03:29:16 -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 28DFF20823; Mon, 4 Mar 2019 08:29:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1551688155; bh=3cF/Yiq5ee9rCDPnZdE60Sgu5RFuQnyZmb82eGccUd0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KXMbMEl2bpLF+QjByqdKyy1YigJMJmDjJJezu8dVX2EdU9fO/zVxaf4/Q+emIdx+4 JxzC6oS0yAZCyiaPkgE1b6z3NvI63dFUmdmwvksnreVSz10coi1xnpd7+MXSO+BaVt bEqy88pG/Brx0ufjO0cPGgLL/PBtVGTKO7+ETP7A= 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 4.19 35/78] sched/wait: Fix rcuwait_wake_up() ordering Date: Mon, 4 Mar 2019 09:22:18 +0100 Message-Id: <20190304081627.070497480@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190304081625.508788074@linuxfoundation.org> References: <20190304081625.508788074@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 4.19-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