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=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 63AF8C432C0 for ; Wed, 27 Nov 2019 20:34:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3CF2020866 for ; Wed, 27 Nov 2019 20:34:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574886874; bh=HekZnTJKsma1+dYnDKSwZvVnS+t1uSfSLjiF7ALpB6U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=MhmA8SsKciVquHXo795viti0XBh2y7AMaBpU1VZoDHKGxrCmMR6cC3heola+Kuf7F bRZHX5xgaEe1cfpMt3s80aeBGvhU/eYs7xMT6fKaWpIMuxDaP3yN112X+uoCn5iXLH /9E4RYkCvLj3u6C3llt0ZpO80AbUqYi6+VXy4oyU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727634AbfK0Ued (ORCPT ); Wed, 27 Nov 2019 15:34:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:35010 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727606AbfK0Uec (ORCPT ); Wed, 27 Nov 2019 15:34:32 -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 63163207DD; Wed, 27 Nov 2019 20:34:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574886871; bh=HekZnTJKsma1+dYnDKSwZvVnS+t1uSfSLjiF7ALpB6U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=c8zrPJtyjYzgWApDRRt9LVV0Riubb+TdUKiim1sgbMnZ86Q1I8wPtvSNVfbi8AZ5D GyC6ps4yD98+eOEF+ruzKRQsSRD1l6D1K5b4uBgj4iXv2k2rxZMRUuiXDsKUAVh/wP WRUw0tNBX8tO0iH+/A8A1CRORAS+qnP5nQ7DATVU= 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 4.4 006/132] mm/ksm.c: dont WARN if page is still mapped in remove_stable_node() Date: Wed, 27 Nov 2019 21:29:57 +0100 Message-Id: <20191127202903.183190560@linuxfoundation.org> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191127202857.270233486@linuxfoundation.org> References: <20191127202857.270233486@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 @@ -714,13 +714,13 @@ 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