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=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 B3A3CC10F11 for ; Wed, 24 Apr 2019 17:13:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8359C21903 for ; Wed, 24 Apr 2019 17:13:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556126002; bh=oGZ5xI8Dp1eexMFikTVd/nehrKrm13+IE1by5Xej0W0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=IGwP+0ywW8gk0LPVmOQTZp9vhpWsNxPq96qQLnw5cvxTtdk7HNZKzXbCjfMq0bqzP 9IemwcSTS7mVDHCGt7BdqH1Q1zDoIv9AOtGDjTVTe+/+7oxHR0IOKaVUZdOCmvNL2l 3bdkbEeKk5PbfVnqitbDunVCCFcEKIqwIY05XDd8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387864AbfDXRNV (ORCPT ); Wed, 24 Apr 2019 13:13:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:37334 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387853AbfDXRNT (ORCPT ); Wed, 24 Apr 2019 13:13:19 -0400 Received: from localhost (62-193-50-229.as16211.net [62.193.50.229]) (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 5E4E2218FE; Wed, 24 Apr 2019 17:13:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556125998; bh=oGZ5xI8Dp1eexMFikTVd/nehrKrm13+IE1by5Xej0W0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=d5YbYZXsA5KRRMbrBjA2ODJ4MieidPVtzqzUg7TJjaxJJy1V8YdyOLDIIcck2CECL Om5rlO4NtcQ7flWl3YER040RkB09Hdio874dI9eqM3ki4d1XwTzQTNo4sqvL/LBwPG Ns7wP+DeL7KSkXvczxD5PvmDg+rcwq+8s7B1+j0o= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mel Gorman , "Peter Zijlstra (Intel)" , Valentin Schneider , Linus Torvalds , Mike Galbraith , Thomas Gleixner , Ingo Molnar Subject: [PATCH 3.18 057/104] sched/fair: Do not re-read ->h_load_next during hierarchical load calculation Date: Wed, 24 Apr 2019 19:09:14 +0200 Message-Id: <20190424170902.929864376@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190424170839.996641496@linuxfoundation.org> References: <20190424170839.996641496@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Mel Gorman commit 0e9f02450da07fc7b1346c8c32c771555173e397 upstream. A NULL pointer dereference bug was reported on a distribution kernel but the same issue should be present on mainline kernel. It occured on s390 but should not be arch-specific. A partial oops looks like: Unable to handle kernel pointer dereference in virtual kernel address space ... Call Trace: ... try_to_wake_up+0xfc/0x450 vhost_poll_wakeup+0x3a/0x50 [vhost] __wake_up_common+0xbc/0x178 __wake_up_common_lock+0x9e/0x160 __wake_up_sync_key+0x4e/0x60 sock_def_readable+0x5e/0x98 The bug hits any time between 1 hour to 3 days. The dereference occurs in update_cfs_rq_h_load when accumulating h_load. The problem is that cfq_rq->h_load_next is not protected by any locking and can be updated by parallel calls to task_h_load. Depending on the compiler, code may be generated that re-reads cfq_rq->h_load_next after the check for NULL and then oops when reading se->avg.load_avg. The dissassembly showed that it was possible to reread h_load_next after the check for NULL. While this does not appear to be an issue for later compilers, it's still an accident if the correct code is generated. Full locking in this path would have high overhead so this patch uses READ_ONCE to read h_load_next only once and check for NULL before dereferencing. It was confirmed that there were no further oops after 10 days of testing. As Peter pointed out, it is also necessary to use WRITE_ONCE() to avoid any potential problems with store tearing. Signed-off-by: Mel Gorman Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Fixes: 685207963be9 ("sched: Move h_load calculation to task_h_load()") Link: https://lkml.kernel.org/r/20190319123610.nsivgf3mjbjjesxb@techsingularity.net Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/sched/fair.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5617,10 +5617,10 @@ static void update_cfs_rq_h_load(struct if (cfs_rq->last_h_load_update == now) return; - cfs_rq->h_load_next = NULL; + WRITE_ONCE(cfs_rq->h_load_next, NULL); for_each_sched_entity(se) { cfs_rq = cfs_rq_of(se); - cfs_rq->h_load_next = se; + WRITE_ONCE(cfs_rq->h_load_next, se); if (cfs_rq->last_h_load_update == now) break; } @@ -5630,7 +5630,7 @@ static void update_cfs_rq_h_load(struct cfs_rq->last_h_load_update = now; } - while ((se = cfs_rq->h_load_next) != NULL) { + while ((se = READ_ONCE(cfs_rq->h_load_next)) != NULL) { load = cfs_rq->h_load; load = div64_ul(load * se->avg.load_avg_contrib, cfs_rq->runnable_load_avg + 1);