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=-5.8 required=3.0 tests=BAYES_00,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 0D030C433E9 for ; Thu, 7 Jan 2021 11:18:32 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 78F6723343 for ; Thu, 7 Jan 2021 11:18:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 78F6723343 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 80F1E8D0133; Thu, 7 Jan 2021 06:18:30 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7BF358D011F; Thu, 7 Jan 2021 06:18:30 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6D4D98D0133; Thu, 7 Jan 2021 06:18:30 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0211.hostedemail.com [216.40.44.211]) by kanga.kvack.org (Postfix) with ESMTP id 5852E8D011F for ; Thu, 7 Jan 2021 06:18:30 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 1AE7B824556B for ; Thu, 7 Jan 2021 11:18:30 +0000 (UTC) X-FDA: 77678730780.28.shock77_0613b77274e9 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin28.hostedemail.com (Postfix) with ESMTP id F2C056C05 for ; Thu, 7 Jan 2021 11:18:29 +0000 (UTC) X-HE-Tag: shock77_0613b77274e9 X-Filterd-Recvd-Size: 4882 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf39.hostedemail.com (Postfix) with ESMTP for ; Thu, 7 Jan 2021 11:18:29 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1610018308; h=from:from:reply-to: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=RQpGpOyPrE4bOtyYyPbs1TfHW7kVTnWw1fBHDIw2fno=; b=PYrkANYpWF+ZDJpX+msYjR159brUpvCPsnc5tplfYlWtO2QGfSMmXxjU+E0dIVwZrhKwOo pfxPlm973ZJSrdwtvKvw2LcE4/HWBd0X/j13V4kEbHldGjhWzOweWXObbWm6NPQY+ll532 VmK0CAc+Q0iWvlU0qJTFUp3sOcm2HXU= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 34BEFAD12; Thu, 7 Jan 2021 11:18:28 +0000 (UTC) Date: Thu, 7 Jan 2021 12:18:27 +0100 From: Michal Hocko To: Muchun Song Cc: Mike Kravetz , Andrew Morton , Naoya Horiguchi , Andi Kleen , Linux Memory Management List , LKML Subject: Re: [External] Re: [PATCH v2 3/6] mm: hugetlb: fix a race between freeing and dissolving the page Message-ID: <20210107111827.GG13207@dhcp22.suse.cz> References: <20210106084739.63318-1-songmuchun@bytedance.com> <20210106084739.63318-4-songmuchun@bytedance.com> <20210106165632.GT13207@dhcp22.suse.cz> <20210107084146.GD13207@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Thu 07-01-21 16:53:13, Muchun Song wrote: > On Thu, Jan 7, 2021 at 4:41 PM Michal Hocko wrote: > > > > On Thu 07-01-21 13:39:38, Muchun Song wrote: > > > On Thu, Jan 7, 2021 at 12:56 AM Michal Hocko wrote: > > > > > > > > On Wed 06-01-21 16:47:36, Muchun Song wrote: > > > > > There is a race condition between __free_huge_page() > > > > > and dissolve_free_huge_page(). > > > > > > > > > > CPU0: CPU1: > > > > > > > > > > // page_count(page) == 1 > > > > > put_page(page) > > > > > __free_huge_page(page) > > > > > dissolve_free_huge_page(page) > > > > > spin_lock(&hugetlb_lock) > > > > > // PageHuge(page) && !page_count(page) > > > > > update_and_free_page(page) > > > > > // page is freed to the buddy > > > > > spin_unlock(&hugetlb_lock) > > > > > spin_lock(&hugetlb_lock) > > > > > clear_page_huge_active(page) > > > > > enqueue_huge_page(page) > > > > > // It is wrong, the page is already freed > > > > > spin_unlock(&hugetlb_lock) > > > > > > > > > > The race windows is between put_page() and spin_lock() which > > > > > is in the __free_huge_page(). > > > > > > > > The race window reall is between put_page and dissolve_free_huge_page. > > > > And the result is that the put_page path would clobber an unrelated page > > > > (either free or already reused page) which is quite serious. > > > > Fortunatelly pages are dissolved very rarely. I believe that user would > > > > require to be privileged to hit this by intention. > > > > > > > > > We should make sure that the page is already on the free list > > > > > when it is dissolved. > > > > > > > > Another option would be to check for PageHuge in __free_huge_page. Have > > > > you considered that rather than add yet another state? The scope of the > > > > spinlock would have to be extended. If that sounds more tricky then can > > > > we check the page->lru in the dissolve path? If the page is still > > > > PageHuge and reference count 0 then there shouldn't be many options > > > > where it can be queued, right? > > > > > > Did you mean that we iterate over the free list to check whether > > > the page is on the free list? > > > > No I meant to check that the page is enqueued which along with ref count > > = 0 should mean it has been released to the pool unless I am missing > > something. > > The page can be on the free list or active list or empty when it > is freed to the pool. How to check whether it is on the free list? As I've said, I might be missing something here. But if the page is freed why does it matter whether it is on a active list or free list from the dissolve operation POV? -- Michal Hocko SUSE Labs