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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 05F50C433E0 for ; Fri, 8 Jan 2021 02:38:55 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7C2E8236F9 for ; Fri, 8 Jan 2021 02:38:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7C2E8236F9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=bytedance.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 732C58D0164; Thu, 7 Jan 2021 21:38:53 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6E2658D0156; Thu, 7 Jan 2021 21:38:53 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5D0728D0164; Thu, 7 Jan 2021 21:38:53 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0007.hostedemail.com [216.40.44.7]) by kanga.kvack.org (Postfix) with ESMTP id 400B08D0156 for ; Thu, 7 Jan 2021 21:38:53 -0500 (EST) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 02C70181AEF30 for ; Fri, 8 Jan 2021 02:38:53 +0000 (UTC) X-FDA: 77681050146.09.bath72_251654f274ef Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin09.hostedemail.com (Postfix) with ESMTP id DD3D2180AD806 for ; Fri, 8 Jan 2021 02:38:52 +0000 (UTC) X-HE-Tag: bath72_251654f274ef X-Filterd-Recvd-Size: 6177 Received: from mail-pl1-f180.google.com (mail-pl1-f180.google.com [209.85.214.180]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Fri, 8 Jan 2021 02:38:52 +0000 (UTC) Received: by mail-pl1-f180.google.com with SMTP id t6so4920360plq.1 for ; Thu, 07 Jan 2021 18:38:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=4zmgQQ/koFoyCFqZqHd/CEfBclNLFL5+ci7EJGrdRVA=; b=F8LuEnnlkXA62BJVlXrdGxp+p35rEVAysJ0KXywPGVixsnKoZorWYmTHSbzjyEX1cu 6JReREQh9aZWC+YPkux2w9e2uZqA1Mi8djI2bKF2/6mZAxXMFQeJVW9Aw+tgo8BjFEPd aFksKmnjXlqAF0JkywhAJyuNgkQLXeFYSHIt9ngMAlugUyIcquP5wTTjGKZx7fmEZk5N YvBhdV8dEi/eR/cn+15+0raiD4KeFSKOenp75hpfLoMBtNwwXmsMBAP4Kg5CNQp7PHsK 4GKNpv5yEZafGYiqyCRB7avkZ9mNmtff+ajJ6IN6/IPx0Ux6S3hqyRGieqqUNNyVVEm5 AEGw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=4zmgQQ/koFoyCFqZqHd/CEfBclNLFL5+ci7EJGrdRVA=; b=Rek7V6cK6H3Qvsjdap01Wng6eD43SO4YjzuG3iAx5L9rN1hiLiMoKJHMh9Y8x5nEW1 FnZzk5xFOHzZ5luMrc+okQJV9WnqsbzJNOdX6i3ZJceHQ4bBXO7yxILIiaovXw5j7xRv 2aukUu5kCbYaR8JzIQeiHGlBYWSyJhOluXQu33H+PkIz6brXBMfrHdodxVGyqiIjIBqQ Kjt97O3d7Wv/UQ0QMPyDBXOW3yukx42QrxRYyEwS3zdm3r2HH7fjEn+VYvaLeS7M6Q+U msjW0t0yNRbwMxV04rVmlmDb5HwNoOPoILcdaKOkrkxLuArVF6vL0Fzp4InvoqFNaPzQ m75g== X-Gm-Message-State: AOAM531DsKcJbPahJhgWMvtigglUvkaPgiZtfu9VjKGfFZWcjS7959G5 OwFmfZBHazBnQe6zAvwe/fDTHEB3+nq3qhkUKAiSNQ== X-Google-Smtp-Source: ABdhPJys/3J9TCNs5W2zE23cKCcRfCrUXDSYSMltBveYwqJe9Yzwi+mY1FkbaxCByDOgONhDCRFnZMzB1Ndm2rNdMbw= X-Received: by 2002:a17:90a:c588:: with SMTP id l8mr1414168pjt.147.1610073531034; Thu, 07 Jan 2021 18:38:51 -0800 (PST) MIME-Version: 1.0 References: <20210106084739.63318-1-songmuchun@bytedance.com> <20210106084739.63318-4-songmuchun@bytedance.com> <20210106165632.GT13207@dhcp22.suse.cz> <20210107084146.GD13207@dhcp22.suse.cz> <20210107111827.GG13207@dhcp22.suse.cz> <20210107123854.GJ13207@dhcp22.suse.cz> <20210107141130.GL13207@dhcp22.suse.cz> In-Reply-To: From: Muchun Song Date: Fri, 8 Jan 2021 10:38:12 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v2 3/6] mm: hugetlb: fix a race between freeing and dissolving the page To: Mike Kravetz Cc: Michal Hocko , Andrew Morton , Naoya Horiguchi , Andi Kleen , Linux Memory Management List , LKML Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jan 8, 2021 at 9:08 AM Mike Kravetz wrote: > > On 1/7/21 7:11 AM, Muchun Song wrote: > > On Thu, Jan 7, 2021 at 10:11 PM Michal Hocko wrote: > >> > >> On Thu 07-01-21 20:59:33, Muchun Song wrote: > >>> On Thu, Jan 7, 2021 at 8:38 PM Michal Hocko wrote: > >> [...] > >>>> Right. Can we simply back off in the dissolving path when ref count is > >>>> 0 && PageHuge() if list_empty(page->lru)? Is there any other scenario > >>>> when the all above is true and the page is not being freed? > >>> > >>> The list_empty(&page->lru) may always return false. > >>> The page before freeing is on the active list > >>> (hstate->hugepage_activelist).Then it is on the free list > >>> after freeing. So list_empty(&page->lru) is always false. > >> > >> The point I was trying to make is that the page has to be enqueued when > >> it is dissolved and freed. If the page is not enqueued then something > >> racing. But then I have realized that this is not a great check to > >> detect the race because pages are going to be released to buddy > >> allocator and that will reuse page->lru again. So scratch that and sorry > >> for the detour. > >> > >> But that made me think some more and one way to reliably detect the race > >> should be PageHuge() check in the freeing path. This is what dissolve > >> path does already. PageHuge becomes false during update_and_free_page() > >> while holding the hugetlb_lock. So can we use that? > > > > It may make the thing complex. Apart from freeing it to the > > buddy allocator, free_huge_page also does something else for > > us. If we detect the race in the freeing path, if it is not a HugeTLB > > page, the freeing path just returns. We also should move those > > things to the dissolve path. Right? > > > > But I find a tricky problem to solve. See free_huge_page(). > > If we are in non-task context, we should schedule a work > > to free the page. We reuse the page->mapping. If the page > > is already freed by the dissolve path. We should not touch > > the page->mapping. So we need to check PageHuge(). > > The check and llist_add() should be protected by > > hugetlb_lock. But we cannot do that. Right? If dissolve > > happens after it is linked to the list. We also should > > remove it from the list (hpage_freelist). It seems to make > > the thing more complex. > > You are correct. This is also an issue/potential problem with this > race. It seems that adding the state information might be the least > complex way to address issue. Yeah, I agree with you. Adding a state is a simple solution. > > -- > Mike Kravetz