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=-11.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,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 545F4C43387 for ; Tue, 15 Jan 2019 16:45:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2353B20645 for ; Tue, 15 Jan 2019 16:45:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547570753; bh=k8bXhqWpO5kaQ3I9FWr8R5h834By14tmBALeMGehoVg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=V7m+Bxx9JhCe2CkkGImpHjTqSxdy4PKeMDzMOMt2UMYB748phyFJT0fo5cs4dcLVE by/qHP5QYVomJ5DJdeQtZ4FGedSpsvDuXmVHF2s/TPQFcmMgN76a4jPfgsQmych2Z7 gNHPFzdNBkycOYKvCZlOF6g2lUT7hfjp5tQPDdOo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387852AbfAOQpq (ORCPT ); Tue, 15 Jan 2019 11:45:46 -0500 Received: from mail.kernel.org ([198.145.29.99]:35384 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731090AbfAOQpl (ORCPT ); Tue, 15 Jan 2019 11:45:41 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.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 1B4A92054F; Tue, 15 Jan 2019 16:45:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547570740; bh=k8bXhqWpO5kaQ3I9FWr8R5h834By14tmBALeMGehoVg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WVstXuddeUA6CnQJY92Drnnj7ArlDJzSkIw1ED1Qw6OcqRlQ8Tl+1YRPEfOXLLjZu ACJQiomh/bf2GRneA4SRaG+pEmTer3l9HQHM2x/jK5l9GRRnurHmsI6QqfH58QRUct Sl2hyKOZeSdSDpE3jlrB5pI88C9ttWIkw5IA3nmw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jan Stancek , "Kirill A. Shutemov" , Michal Hocko , "Kirill A. Shutemov" , David Hildenbrand , Andrea Arcangeli , Andrew Morton , Linus Torvalds , Laszlo Ersek Subject: [PATCH 4.20 53/57] mm: page_mapped: dont assume compound page is huge or THP Date: Tue, 15 Jan 2019 17:36:34 +0100 Message-Id: <20190115154913.994745402@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190115154910.734892368@linuxfoundation.org> References: <20190115154910.734892368@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore 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 4.20-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jan Stancek commit 8ab88c7169b7fba98812ead6524b9d05bc76cf00 upstream. LTP proc01 testcase has been observed to rarely trigger crashes on arm64: page_mapped+0x78/0xb4 stable_page_flags+0x27c/0x338 kpageflags_read+0xfc/0x164 proc_reg_read+0x7c/0xb8 __vfs_read+0x58/0x178 vfs_read+0x90/0x14c SyS_read+0x60/0xc0 The issue is that page_mapped() assumes that if compound page is not huge, then it must be THP. But if this is 'normal' compound page (COMPOUND_PAGE_DTOR), then following loop can keep running (for HPAGE_PMD_NR iterations) until it tries to read from memory that isn't mapped and triggers a panic: for (i = 0; i < hpage_nr_pages(page); i++) { if (atomic_read(&page[i]._mapcount) >= 0) return true; } I could replicate this on x86 (v4.20-rc4-98-g60b548237fed) only with a custom kernel module [1] which: - allocates compound page (PAGEC) of order 1 - allocates 2 normal pages (COPY), which are initialized to 0xff (to satisfy _mapcount >= 0) - 2 PAGEC page structs are copied to address of first COPY page - second page of COPY is marked as not present - call to page_mapped(COPY) now triggers fault on access to 2nd COPY page at offset 0x30 (_mapcount) [1] https://github.com/jstancek/reproducers/blob/master/kernel/page_mapped_crash/repro.c Fix the loop to iterate for "1 << compound_order" pages. Kirrill said "IIRC, sound subsystem can producuce custom mapped compound pages". Link: http://lkml.kernel.org/r/c440d69879e34209feba21e12d236d06bc0a25db.1543577156.git.jstancek@redhat.com Fixes: e1534ae95004 ("mm: differentiate page_mapped() from page_mapcount() for compound pages") Signed-off-by: Jan Stancek Debugged-by: Laszlo Ersek Suggested-by: "Kirill A. Shutemov" Acked-by: Michal Hocko Acked-by: Kirill A. Shutemov Reviewed-by: David Hildenbrand Reviewed-by: Andrea Arcangeli Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/util.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/util.c +++ b/mm/util.c @@ -478,7 +478,7 @@ bool page_mapped(struct page *page) return true; if (PageHuge(page)) return false; - for (i = 0; i < hpage_nr_pages(page); i++) { + for (i = 0; i < (1 << compound_order(page)); i++) { if (atomic_read(&page[i]._mapcount) >= 0) return true; }