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=-3.8 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 autolearn=no 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 23579C432C0 for ; Fri, 22 Nov 2019 01:54:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D26F2206D7 for ; Fri, 22 Nov 2019 01:54:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="HAehkxSo" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D26F2206D7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 79E5D6B049A; Thu, 21 Nov 2019 20:54:04 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 751326B049B; Thu, 21 Nov 2019 20:54:04 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6904B6B049C; Thu, 21 Nov 2019 20:54:04 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0033.hostedemail.com [216.40.44.33]) by kanga.kvack.org (Postfix) with ESMTP id 53AD26B049A for ; Thu, 21 Nov 2019 20:54:04 -0500 (EST) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id DE181824999B for ; Fri, 22 Nov 2019 01:54:03 +0000 (UTC) X-FDA: 76182242766.15.neck88_5da6537e0c61a X-HE-Tag: neck88_5da6537e0c61a X-Filterd-Recvd-Size: 3241 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf15.hostedemail.com (Postfix) with ESMTP for ; Fri, 22 Nov 2019 01:54:03 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (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 49931206DA; Fri, 22 Nov 2019 01:54:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574387642; bh=EsdBhVEjhAGhB+ttu3hBaGhwQ4Q0+rsLVS9kMNRTn2E=; h=Date:From:To:Subject:From; b=HAehkxSoZY5pr1Salw1CWfgkBZD2HyyKxDaJsY7IfQlTsEHUI7XJHh2rll1BaZrrp CLQuQ6jJa9ZfnqzOjmiqL/1dukNN7WTMWN20dRYf20YgSamjrYHiOU47npfgOfZwAu erAsaQI2pkTeUFiJtAy+fSi3nQLr6IddVAqVB2h0= Date: Thu, 21 Nov 2019 17:54:01 -0800 From: akpm@linux-foundation.org To: aarcange@redhat.com, akpm@linux-foundation.org, aryabinin@virtuozzo.com, hughd@google.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, stable@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 4/4] mm/ksm.c: don't WARN if page is still mapped in remove_stable_node() Message-ID: <20191122015401.XFgHUZogP%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 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: From: Andrey Ryabinin Subject: mm/ksm.c: don't WARN if page is still mapped in remove_stable_node() 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 --- mm/ksm.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) --- a/mm/ksm.c~mm-ksm-dont-warn-if-page-is-still-mapped-in-remove_stable_node +++ a/mm/ksm.c @@ -885,13 +885,13 @@ 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 _