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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5066CEEAA65 for ; Thu, 14 Sep 2023 19:09:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240927AbjINTJO (ORCPT ); Thu, 14 Sep 2023 15:09:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33804 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230311AbjINTJN (ORCPT ); Thu, 14 Sep 2023 15:09:13 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CDD3D1FC7 for ; Thu, 14 Sep 2023 12:09:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=7/m3bz/FMIYfip9hzUryY5fsZo8BtjCMUb7iqvvNxc8=; b=KBQHYU+OC2p0pEcUvBBR0Be/w3 g5TVCjkKEIo7PSyc6KjLHHhobgiWZGpRszgsixVRz3zDMHXAKV/mS7d+r1zhcXJ9tZe+uHIZkPhQQ d79lQHtWTNXPq03Mzly1jE08YbUvHNIdlCpSXW7YefWSf7FUfAJlhPUE5ywPX9XLa+CkYcLoAhLLQ 9nznEIOxVBg5MHP/zQ7eezP0NgPoypT91tJ1RvbOx+4zFvl+KLI7fgLtoxOwp+BOKU/SEfb+gBKnx jxA7Y8l4ORamvaeN2oP5IGzMFtTBu6oLKjHGju9pdfpr1JxSHssXh68Q5y9OjaeFEfoy9CR1wzR5p DCqOIWsw==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qgri3-004eEd-Ck; Thu, 14 Sep 2023 19:09:03 +0000 Date: Thu, 14 Sep 2023 20:09:03 +0100 From: Matthew Wilcox To: Suren Baghdasaryan Cc: syzbot , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [mm?] kernel BUG in vma_replace_policy Message-ID: References: <000000000000f392a60604a65085@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 14, 2023 at 06:20:56PM +0000, Suren Baghdasaryan wrote: > I think I found the problem and the explanation is much simpler. While > walking the page range, queue_folios_pte_range() encounters an > unmovable page and queue_folios_pte_range() returns 1. That causes a > break from the loop inside walk_page_range() and no more VMAs get > locked. After that the loop calling mbind_range() walks over all VMAs, > even the ones which were skipped by queue_folios_pte_range() and that > causes this BUG assertion. > > Thinking what's the right way to handle this situation (what's the > expected behavior here)... > I think the safest way would be to modify walk_page_range() and make > it continue calling process_vma_walk_lock() for all VMAs in the range > even when __walk_page_range() returns a positive err. Any objection or > alternative suggestions? So we only return 1 here if MPOL_MF_MOVE* & MPOL_MF_STRICT were specified. That means we're going to return an error, no matter what, and there's no point in calling mbind_range(). Right? +++ b/mm/mempolicy.c @@ -1334,6 +1334,8 @@ static long do_mbind(unsigned long start, unsigned long len, ret = queue_pages_range(mm, start, end, nmask, flags | MPOL_MF_INVERT, &pagelist, true); + if (ret == 1) + ret = -EIO; if (ret < 0) { err = ret; goto up_out; (I don't really understand this code, so it can't be this simple, can it? Why don't we just return -EIO from queue_folios_pte_range() if this is the right answer?)