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 B024FC433E0 for ; Fri, 8 Jan 2021 10:09:39 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 17CD1235FA for ; Fri, 8 Jan 2021 10:09:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 17CD1235FA 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 73EB08D0176; Fri, 8 Jan 2021 05:09:38 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6EF4B8D0156; Fri, 8 Jan 2021 05:09:38 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 62C048D0176; Fri, 8 Jan 2021 05:09:38 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0238.hostedemail.com [216.40.44.238]) by kanga.kvack.org (Postfix) with ESMTP id 4C47B8D0156 for ; Fri, 8 Jan 2021 05:09:38 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 1302E824556B for ; Fri, 8 Jan 2021 10:09:38 +0000 (UTC) X-FDA: 77682186036.30.trees46_0d0a3d8274f2 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin30.hostedemail.com (Postfix) with ESMTP id CBFDA180B3AB8 for ; Fri, 8 Jan 2021 10:09:37 +0000 (UTC) X-HE-Tag: trees46_0d0a3d8274f2 X-Filterd-Recvd-Size: 6093 Received: from mail-pg1-f179.google.com (mail-pg1-f179.google.com [209.85.215.179]) by imf44.hostedemail.com (Postfix) with ESMTP for ; Fri, 8 Jan 2021 10:09:36 +0000 (UTC) Received: by mail-pg1-f179.google.com with SMTP id z21so7371981pgj.4 for ; Fri, 08 Jan 2021 02:09:36 -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=hxBxmBs8fMYMIca2A29vy77BSWo76sDthhhEV0f2l40=; b=U7xIOEzOJHEbpaStAALRTWL/4LQl3vVyN295Pv9lgnMKByxJgJ3e0l1HA1xRKDZxJo zEgxZ5Dxra2np48BibHXkl1OoePEeJWFDe3t4xYtztx5AEpzgdyHirrizSQWRaImlYYw 8r9X2/exvcylj2szVQWKxrnBPaTCScdQy2nx/8vSAX62q5U5iybw+mb34M/yMvbESFD5 i87v1xCkNcT/vRBqyXwpl5+w4srPdufRjiVtLuuPgiejuHaSfVPBnhSThDUpLJLqnDs5 lMyV3o0Qz4u6wUnPgu3o/kWIlIdPfjcvAEDcLopakBNTKN3hZfgoR71oPKZ7XYn21C3N TAnA== 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=hxBxmBs8fMYMIca2A29vy77BSWo76sDthhhEV0f2l40=; b=GNjVQjOoFDnHEAkjfGstQMo0vweufoEN00j0YT1zerNHfIKY3il18uMuJ5jYcCDf7G s8Z48M57EbV2kR1A+kHZZCypnVG0ocaKvnxLwY48Bdwq9BcsfhX2OM9cyubEjoctQBan q5Axkzscf+rlY1BgXm9QZ2aB1BPVQVPmrtq8AISrf7yzSsIR7w8HXFIJfQuuvX0TtKK1 0Q9tMhsbD3Z+QTLB33N0zaPnAeO6vNHXW+bNcidmNe/nQ0e+pzSfQSRR84YjLu3NiGwm oYPTCw7DvkCZmJ1GELCX11A3bGi8wX/DtQCSyNm1HCojsnq3shBABXi5TTiu+QPFYgoc rSbQ== X-Gm-Message-State: AOAM532+QizpmEq5W7/UeluEYvEc/cSEX9Lkt6izBsWDIGhZNCUel8ws mzai/hUeamt6LkEOZoPzq1ZbCaeOnwLOeTj7Djw3ww== X-Google-Smtp-Source: ABdhPJzINUIAUuzfr9rwth5LMHR0iF7mo8xQp9/UO7OVzEZTtkHOV8K4XtkpNLfPF/XkJsTxJ1qbOpZncY0yIxH4U+M= X-Received: by 2002:a63:480f:: with SMTP id v15mr6252552pga.341.1610100575749; Fri, 08 Jan 2021 02:09:35 -0800 (PST) MIME-Version: 1.0 References: <20210107084146.GD13207@dhcp22.suse.cz> <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> In-Reply-To: <20210108093136.GY13207@dhcp22.suse.cz> From: Muchun Song Date: Fri, 8 Jan 2021 18:08:57 +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" 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 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. task context: interrupt context: put_page(page) spin_lock(&hugetlb_lock) put_page(page) spin_lock(&hugetlb_lock) // deadlock spin_unlock(&hugetlb_lock) > Although it would be much more nicer if the lock was held at this layer > rather than both free_huge_page and __free_huge_page. But that clean up > can be done on top. > > -- > Michal Hocko > SUSE Labs