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=-8.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 8F307C433E0 for ; Fri, 8 Jan 2021 11:54:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A26623A03 for ; Fri, 8 Jan 2021 11:54:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726735AbhAHLyQ (ORCPT ); Fri, 8 Jan 2021 06:54:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58984 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725884AbhAHLyP (ORCPT ); Fri, 8 Jan 2021 06:54:15 -0500 Received: from mail-pj1-x102c.google.com (mail-pj1-x102c.google.com [IPv6:2607:f8b0:4864:20::102c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 754D5C0612F4 for ; Fri, 8 Jan 2021 03:53:35 -0800 (PST) Received: by mail-pj1-x102c.google.com with SMTP id v1so3518321pjr.2 for ; Fri, 08 Jan 2021 03:53:35 -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=GW5q2722koIbZXnDnSvwWdTVIWeItYho+2jBeLd21CQ=; b=H2kYfvBdyX/hs0s4f/V4SVCbXiBDZvNV7nHlCFFj9Hivaz3hVXYb6c8D9A7NkS4+a+ GVrJmBTOwgLbI1Dyd1b+ixHcAiZoJbl8/4V/Y+WQ47gAK7ji8aAReFpnMhKOa2bbZ8z5 M4V5a1k0MGdrkeRXhOrauoTX82PlcHg0kQ3hxOIr0gjvakcNfBcfOcC3fO9TKGxyGn7r yrPasq5bmubbz5KbAWqFIO/6SdGbEajkp4+MCkaTxs6Cu7rKj3BA/bhTz++qqtLkrixF 8oWV72jWjyE3dPvd+Pw/hCd2sXD3mJGm4QkSE4M38cqIkLPnEpQZgmFSfAVd3dVfA2Eg i2Rg== 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=GW5q2722koIbZXnDnSvwWdTVIWeItYho+2jBeLd21CQ=; b=nPVs9v2SJQTsZldHglCjnMAJZ3gJGJBiRWojTEzDftu4H32JZ+EcnQOUjOUu4DHAaQ nCCnaVYTdUlzGPqwdGeWl9fXad39YcWGfw4WRJJc/oOissxENxo13mtnlnh4v6IZrReP J4l6fTP79OqTcR2ssfju654eJXwcW7LbA3bFDMO/AUp/RcLsChuZMJcTNwPrk5xEHeRC CscknnYrEWsR/VQSc0twLqlZS1u6wyNKYrFdgS0ln5xxg/4Sxya4aXm8/oODL3ImrP59 DW+JmRftOFoewvqiEeKmlfhSTHhEqPWP83825dTVPChtKcmktncWyWZoalfsqYlt8jK4 fMjA== X-Gm-Message-State: AOAM533Y69OJmr0rMrv/8c+toP8JlcSv7gSg5KABpUl9PnCVpNovdPil uaRJlr+lOno4tDgA7kTkN8LyQrkMdfLt0xvQ+EuEzaeTRV5LDGuzfC0= X-Google-Smtp-Source: ABdhPJyYEuk6apHjhRQbzXazmjDwQQiU+D+mGB6hMBDpiuuuIqjPZIey46A90m26h64vrzoVndUSWOOV0CgSG4xhypI= X-Received: by 2002:a17:90a:5405:: with SMTP id z5mr3456077pjh.13.1610106814984; Fri, 08 Jan 2021 03:53:34 -0800 (PST) MIME-Version: 1.0 References: <20210107111827.GG13207@dhcp22.suse.cz> <20210107123854.GJ13207@dhcp22.suse.cz> <20210107141130.GL13207@dhcp22.suse.cz> <20210108084330.GW13207@dhcp22.suse.cz> <20210108093136.GY13207@dhcp22.suse.cz> <20210108114411.GZ13207@dhcp22.suse.cz> In-Reply-To: <20210108114411.GZ13207@dhcp22.suse.cz> From: Muchun Song Date: Fri, 8 Jan 2021 19:52:54 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v2 3/6] mm: hugetlb: fix a race between freeing and dissolving the page To: Michal Hocko Cc: Mike Kravetz , Andrew Morton , Naoya Horiguchi , Andi Kleen , Linux Memory Management List , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 8, 2021 at 7:44 PM Michal Hocko wrote: > > On Fri 08-01-21 18:08:57, Muchun Song wrote: > > On Fri, Jan 8, 2021 at 5:31 PM Michal Hocko wrote: > > > > > > On Fri 08-01-21 17:01:03, Muchun Song wrote: > > > > On Fri, Jan 8, 2021 at 4:43 PM Michal Hocko wrote: > > > > > > > > > > On Thu 07-01-21 23:11:22, Muchun Song wrote: > > > [..] > > > > > > 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. > > > > > > > > > > I am not sure I follow you here but yes PageHuge under hugetlb_lock > > > > > should be the reliable way to check for the race. I am not sure why we > > > > > really need to care about mapping or other state. > > > > > > > > CPU0: CPU1: > > > > free_huge_page(page) > > > > if (PageHuge(page)) > > > > dissolve_free_huge_page(page) > > > > spin_lock(&hugetlb_lock) > > > > update_and_free_page(page) > > > > spin_unlock(&hugetlb_lock) > > > > llist_add(page->mapping) > > > > // the mapping is corrupted > > > > > > > > The PageHuge(page) and llist_add() should be protected by > > > > hugetlb_lock. Right? If so, we cannot hold hugetlb_lock > > > > in free_huge_page() path. > > > > > > OK, I see. I completely forgot about this snowflake. I thought that > > > free_huge_page was a typo missing initial __. Anyway you are right that > > > this path needs a check as well. But I don't see why we couldn't use the > > > lock here. The lock can be held only inside the !in_task branch. > > > > Because we hold the hugetlb_lock without disable irq. So if an interrupt > > occurs after we hold the lock. And we also free a HugeTLB page. Then > > it leads to deadlock. > > There is nothing really to prevent making hugetlb_lock irq safe, isn't > it? Yeah. We can make the hugetlb_lock irq safe. But why have we not done this? Maybe the commit changelog can provide more information. See https://github.com/torvalds/linux/commit/c77c0a8ac4c522638a8242fcb9de9496e3cdbb2d > -- > Michal Hocko > SUSE Labs