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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 B8730ECE588 for ; Tue, 15 Oct 2019 16:26:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B8C82086A for ; Tue, 15 Oct 2019 16:26:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="sUQkRGtM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728722AbfJOQ0O (ORCPT ); Tue, 15 Oct 2019 12:26:14 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:48952 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725804AbfJOQ0O (ORCPT ); Tue, 15 Oct 2019 12:26:14 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=ZypuQh7t9PSVnbgbqJqaj9CAuSfysI8ltXj5dIpJ8G0=; b=sUQkRGtMMKhj+o8Na0PSwNgFi KYfWXWqFNAwHhz0Tl6vVI1jKcsQQ9DEjLiWfgTxj6L88kCspWFYdU3UsYjJIPa3wO/JOXxRlhyTG1 r/+Uwzd/wOUZGP2id3Tah0Otv9oUx2flap59++DMFxNZ257Clvx8zl5Cm6nJ4zwc0Qg30qe10XpEq 6V5YEUgeR8MQXT8cS8h9YsmFQdo1o9VeBXI8RNZqtdRbT6nr3gsbfBYKr09iSESV7n+axCAuVCb9H vTQQrNYEII2TjJPN3XSTKnZKmW16sKwqS7NrT6TOHVs6QyhDxad/ESgYcViL4RdGChwjDtUEbsO0g OyPy0SVyg==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1iKPeD-0005yz-Lt; Tue, 15 Oct 2019 16:26:09 +0000 Date: Tue, 15 Oct 2019 09:26:09 -0700 From: Matthew Wilcox To: Sebastian Andrzej Siewior Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Frank Rowand , Peter Zijlstra , Thomas Gleixner , Steven Rostedt Subject: Re: [PATCH RT] Revert "ARM: Initialize split page table locks for vector page" Message-ID: <20191015162609.GH32665@bombadil.infradead.org> References: <20191014160238.enawbbfcxnbdrlch@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191014160238.enawbbfcxnbdrlch@linutronix.de> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 14, 2019 at 06:02:38PM +0200, Sebastian Andrzej Siewior wrote: > I'm dropping this patch, with its original description: > > |ARM: Initialize split page table locks for vector page > | > |Without this patch, ARM can not use SPLIT_PTLOCK_CPUS if > |PREEMPT_RT_FULL=y because vectors_user_mapping() creates a > |VM_ALWAYSDUMP mapping of the vector page (address 0xffff0000), but no > |ptl->lock has been allocated for the page. An attempt to coredump > |that page will result in a kernel NULL pointer dereference when > |follow_page() attempts to lock the page. > | > |The call tree to the NULL pointer dereference is: > | > | do_notify_resume() > | get_signal_to_deliver() > | do_coredump() > | elf_core_dump() > | get_dump_page() > | __get_user_pages() > | follow_page() > | pte_offset_map_lock() <----- a #define > | ... > | rt_spin_lock() > | > |The underlying problem is exposed by mm-shrink-the-page-frame-to-rt-size.patch. > > The patch named mm-shrink-the-page-frame-to-rt-size.patch was dropped > from the RT queue once the SPLIT_PTLOCK_CPUS feature (in a slightly > different shape) went upstream (somewhere between v3.12 and v3.14). > > I can see that the patch still allocates a lock which wasn't there > before. However I can't trigger a kernel oops like described in the > patch by triggering a coredump. Did your test build have ALLOC_SPLIT_PTLOCKS defined?