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=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 369AFC2D0E2 for ; Tue, 22 Sep 2020 15:49:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E1D3F23A1E for ; Tue, 22 Sep 2020 15:49:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="CUeeEnbi" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726719AbgIVPs7 (ORCPT ); Tue, 22 Sep 2020 11:48:59 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:59032 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726589AbgIVPs7 (ORCPT ); Tue, 22 Sep 2020 11:48:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600789738; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=5WSEXBgGTOxpyvYjGWGStBPmhuahuiY9FhGyjHnpfvI=; b=CUeeEnbi6mVUD7vC3zZiO/s42ZHAbgFhRw1hy6btzKa+E68GUf+FMkuBwrrgUykjt+iBWh QerUQyepbDKx87LkOrHacIG/jn5KVKz16AiHuqViIkUm4BkkYTRRcmE6NwSXnIj2Fc8unz b4ytNcDwcsIWaE6x8wE09g6bjZM7FCU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-358-i7QyB6gzMpGIsuboqX56xg-1; Tue, 22 Sep 2020 11:48:54 -0400 X-MC-Unique: i7QyB6gzMpGIsuboqX56xg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 556A88064BA; Tue, 22 Sep 2020 15:48:52 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.146]) by smtp.corp.redhat.com (Postfix) with SMTP id 4DA6981C41; Tue, 22 Sep 2020 15:48:47 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 22 Sep 2020 17:48:52 +0200 (CEST) Date: Tue, 22 Sep 2020 17:48:46 +0200 From: Oleg Nesterov To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jason Gunthorpe , Andrew Morton , Jan Kara , Michal Hocko , Kirill Tkhai , Kirill Shutemov , Hugh Dickins , Christoph Hellwig , Andrea Arcangeli , John Hubbard , Leon Romanovsky , Linus Torvalds , Jann Horn Subject: Re: [PATCH 3/5] mm: Rework return value for copy_one_pte() Message-ID: <20200922154845.GE11679@redhat.com> References: <20200921211744.24758-1-peterx@redhat.com> <20200921211744.24758-4-peterx@redhat.com> <20200922100840.GA11679@redhat.com> <20200922101815.GB11679@redhat.com> <20200922153612.GF19098@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200922153612.GF19098@xz-x1> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/22, Peter Xu wrote: > > On Tue, Sep 22, 2020 at 12:18:16PM +0200, Oleg Nesterov wrote: > > On 09/22, Oleg Nesterov wrote: > > > > > > On 09/21, Peter Xu wrote: > > > > > > > > @@ -866,13 +877,18 @@ static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm, > > > > pte_unmap_unlock(orig_dst_pte, dst_ptl); > > > > cond_resched(); > > > > > > > > - if (entry.val) { > > > > - if (add_swap_count_continuation(entry, GFP_KERNEL) < 0) > > > > + switch (copy_ret) { > > > > + case COPY_MM_SWAP_CONT: > > > > + if (add_swap_count_continuation(data.entry, GFP_KERNEL) < 0) > > > > return -ENOMEM; > > > > - progress = 0; > > > > + break; > > > > > > Note that you didn't clear copy_ret, it is still COPY_MM_SWAP_CONT, > > > > > > > + default: > > > > + break; > > > > } > > > > + > > > > if (addr != end) > > > > goto again; > > > > > > After that the main loop can stop again because of need_resched(), and > > > in this case add_swap_count_continuation(data.entry) will be called again? > > > > No, this is not possible, copy_one_pte() should be called at least once, > > progress = 0 before restart. Sorry for noise. > > Oh wait, I think you're right... when we get a COPY_MM_SWAP_CONT, goto "again", > then if there're 32 pte_none() ptes _plus_ an need_resched(), then we might > reach again at the same add_swap_count_continuation() with the same swp entry. Yes, please see my reply to 4/5 ;) > However since I didn't change this logic in this patch, it probably means this > bug is also in the original code before this series... I'm thinking maybe I > should prepare a standalone patch to clear the swp_entry_t and cc stable. Well, if copy_one_pte(src_pte) hits a swap entry and returns entry.val != 0, then pte_none(*src_pte) is not possible after restart? This means that copy_one_pte() will be called at least once. So _think_ that the current code is fine, but I can be easily wrong and I agree this doesn't look clean. Oleg.