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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 8712CC432C3 for ; Tue, 19 Nov 2019 13:19:25 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0EB1E21D7F for ; Tue, 19 Nov 2019 13:19:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0EB1E21D7F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=virtuozzo.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5E93E6B000A; Tue, 19 Nov 2019 08:19:24 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 571A36B000C; Tue, 19 Nov 2019 08:19:24 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 461EB6B000D; Tue, 19 Nov 2019 08:19:24 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0069.hostedemail.com [216.40.44.69]) by kanga.kvack.org (Postfix) with ESMTP id 2DA496B000A for ; Tue, 19 Nov 2019 08:19:24 -0500 (EST) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id D6AFF180AD815 for ; Tue, 19 Nov 2019 13:19:23 +0000 (UTC) X-FDA: 76173083406.13.sort73_51fb438191a41 X-HE-Tag: sort73_51fb438191a41 X-Filterd-Recvd-Size: 2576 Received: from relay.sw.ru (relay.sw.ru [185.231.240.75]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Tue, 19 Nov 2019 13:19:23 +0000 (UTC) Received: from dhcp-172-16-25-5.sw.ru ([172.16.25.5] helo=i7.sw.ru) by relay.sw.ru with esmtp (Exim 4.92.3) (envelope-from ) id 1iX3PT-0007Sl-0S; Tue, 19 Nov 2019 16:19:11 +0300 From: Andrey Ryabinin To: Andrew Morton Cc: Hugh Dickins , Andrea Arcangeli , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Ryabinin , stable@vger.kernel.org Subject: [PATCH] mm/ksm: Don't WARN if page is still mapped in remove_stable_node() Date: Tue, 19 Nov 2019 16:18:50 +0300 Message-Id: <20191119131850.5675-1-aryabinin@virtuozzo.com> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. Fixes: cbf86cfe04a6 ("ksm: remove old stable nodes more thoroughly") Signed-off-by: Andrey Ryabinin Cc: --- mm/ksm.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index dbee2eb4dd05..7905934cd3ad 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -885,13 +885,13 @@ static int remove_stable_node(struct stable_node *s= table_node) return 0; } =20 - 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 =3D -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 =3D -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 --=20 2.23.0