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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 279A0C43215 for ; Wed, 27 Nov 2019 21:30:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F3A7C20665 for ; Wed, 27 Nov 2019 21:30:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574890242; bh=MTXxrypDEJvyoxSioOfbN3iV+2WTuL9ZZHwwufuetbs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=F5gaiZ+KUWrHheFrdwLN8vXzhXKGi5IIU+I3KPci6I5LhIrrSspGDhu/xcCTqNIXS 4KYnRBUwlKzf9Nd9QDjpOaAdhk9FYvCSsYbFRFAMZViHraEessD+vQOd6ldmS4kHf/ yNoF2etkHKdwT23A45nNvkrMEP60pALIdKcEwUZU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730647AbfK0Uzg (ORCPT ); Wed, 27 Nov 2019 15:55:36 -0500 Received: from mail.kernel.org ([198.145.29.99]:46058 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730965AbfK0Uzc (ORCPT ); Wed, 27 Nov 2019 15:55:32 -0500 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 5167E21582; Wed, 27 Nov 2019 20:55:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574888131; bh=MTXxrypDEJvyoxSioOfbN3iV+2WTuL9ZZHwwufuetbs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LIN3u2tpU3UrqZN01O5YzV0vie1tf0x9UFcaYzIi3Y7mNx4ndeJM0f74cJVLN2tmB CXY0Pf0u/dgzqhyapkgsogkcR+gpAnVx0HVH4WlTZHky9Ol2rgLILKfr8piWVIx9aU AexofUUC9lVLcF5cGpmrnwNYWmr4f1v3Rkg0SvCc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andrey Ryabinin , Hugh Dickins , Andrea Arcangeli , Andrew Morton , Linus Torvalds Subject: [PATCH 4.19 017/306] mm/ksm.c: dont WARN if page is still mapped in remove_stable_node() Date: Wed, 27 Nov 2019 21:27:47 +0100 Message-Id: <20191127203115.954898981@linuxfoundation.org> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191127203114.766709977@linuxfoundation.org> References: <20191127203114.766709977@linuxfoundation.org> User-Agent: quilt/0.66 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 From: Andrey Ryabinin commit 9a63236f1ad82d71a98aa80320b6cb618fb32f44 upstream. It's possible to hit the WARN_ON_ONCE(page_mapped(page)) in remove_stable_node() when it races with __mmput() and squeezes in between ksm_exit() and exit_mmap(). WARNING: CPU: 0 PID: 3295 at mm/ksm.c:888 remove_stable_node+0x10c/0x150 Call Trace: remove_all_stable_nodes+0x12b/0x330 run_store+0x4ef/0x7b0 kernfs_fop_write+0x200/0x420 vfs_write+0x154/0x450 ksys_write+0xf9/0x1d0 do_syscall_64+0x99/0x510 entry_SYSCALL_64_after_hwframe+0x49/0xbe Remove the warning as there is nothing scary going on. Link: http://lkml.kernel.org/r/20191119131850.5675-1-aryabinin@virtuozzo.com Fixes: cbf86cfe04a6 ("ksm: remove old stable nodes more thoroughly") Signed-off-by: Andrey Ryabinin Acked-by: Hugh Dickins Cc: Andrea Arcangeli Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/ksm.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) --- a/mm/ksm.c +++ b/mm/ksm.c @@ -870,13 +870,13 @@ static int remove_stable_node(struct sta return 0; } - if (WARN_ON_ONCE(page_mapped(page))) { - /* - * This should not happen: but if it does, just refuse to let - * merge_across_nodes be switched - there is no need to panic. - */ - err = -EBUSY; - } else { + /* + * Page could be still mapped if this races with __mmput() running in + * between ksm_exit() and exit_mmap(). Just refuse to let + * merge_across_nodes/max_page_sharing be switched. + */ + err = -EBUSY; + if (!page_mapped(page)) { /* * The stable node did not yet appear stale to get_ksm_page(), * since that allows for an unmapped ksm page to be recognized