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=-5.3 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 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 1E720C4363D for ; Tue, 22 Sep 2020 15:36:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C369C2388B for ; Tue, 22 Sep 2020 15:36:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="D7SpHD/M" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726731AbgIVPgT (ORCPT ); Tue, 22 Sep 2020 11:36:19 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:58763 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726566AbgIVPgT (ORCPT ); Tue, 22 Sep 2020 11:36:19 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600788978; 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=9qUAnZcDPIOTE8chUJkXUfmB3Qkup6kzfAgtjloNLEI=; b=D7SpHD/MSDqyl/Isg0aKiGQhr8iongeuGCxvzAQKchoW0S9P8Itvd6/layAOIXHtfrK3+Y 5TqGzpYKGQ0KwvuWu0kHwLr8Y3rUjadrMlovyDZIMk5mYB4oItkQjD6wk5NWo/bIHZpiym N3plq7JoDxjo/s4c0uhn4hXK0+FkiFQ= Received: from mail-qt1-f199.google.com (mail-qt1-f199.google.com [209.85.160.199]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-523-yy8jg3zsMByaHDUKirfgmw-1; Tue, 22 Sep 2020 11:36:16 -0400 X-MC-Unique: yy8jg3zsMByaHDUKirfgmw-1 Received: by mail-qt1-f199.google.com with SMTP id e6so16305949qtg.13 for ; Tue, 22 Sep 2020 08:36:15 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=9qUAnZcDPIOTE8chUJkXUfmB3Qkup6kzfAgtjloNLEI=; b=ldtbYkJVclAMOmmxITuZixF+g/dFkytmmHbIg1Tn6I96IwlNxuyIh1eG/hHB2cU+YH k+lbE9lSmd6U/NSRVlL+XwVlO5az5f+VXasNtLulLvaU1hDgb3pBOQYHVx+LNet9/FQ4 TiLv1MS+ebxz0/WoEOiga03nZnLQLqMJrHBaX9fCSUFd7JulEusKlSVO0dG0Z78eGMlB tjjGzLUeDMSGrtkQWIcYA4XRMobYz/7N1lTAU5tGXHLZJsng2KqWTN8QJF8WzimQCxoQ QJzZYtmwJqOU3l22PM32bXb6Vc+YI0u+V32gCvSMJ98MiDNlL9vw0aexZGZ6rst5pt3v 57Fw== X-Gm-Message-State: AOAM532iV+i3dp5eRazXr4D/yo4J7wntyxpBuTsXZgh1i7w/vEYJQLc/ f8WLIdQAzCgfbqy+3qIaOsxB3Y1y9b8dfaHCY35ZHDuatWY0gPeeb7ML4h7chXYKxT+Y3bAKHrB Hd2OG9Vg+f40YyOQUCoY7sWd4 X-Received: by 2002:a37:8883:: with SMTP id k125mr5113342qkd.387.1600788975030; Tue, 22 Sep 2020 08:36:15 -0700 (PDT) X-Google-Smtp-Source: ABdhPJw3nN2tbkiA28XqYXkWFBSdDPKBDK4RDcM0qhYUN5Ac6FIwGRsUoFXx4b9P9kPZ3JzBgvSuyw== X-Received: by 2002:a37:8883:: with SMTP id k125mr5113311qkd.387.1600788974750; Tue, 22 Sep 2020 08:36:14 -0700 (PDT) Received: from xz-x1 (bras-vprn-toroon474qw-lp130-11-70-53-122-15.dsl.bell.ca. [70.53.122.15]) by smtp.gmail.com with ESMTPSA id v16sm11433232qkg.37.2020.09.22.08.36.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2020 08:36:14 -0700 (PDT) Date: Tue, 22 Sep 2020 11:36:12 -0400 From: Peter Xu To: Oleg Nesterov 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: <20200922153612.GF19098@xz-x1> References: <20200921211744.24758-1-peterx@redhat.com> <20200921211744.24758-4-peterx@redhat.com> <20200922100840.GA11679@redhat.com> <20200922101815.GB11679@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200922101815.GB11679@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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. Thanks, -- Peter Xu