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 C81C0C433DB for ; Thu, 7 Jan 2021 08:40:43 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5F0D42311E for ; Thu, 7 Jan 2021 08:40:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5F0D42311E 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 BC1C68D0128; Thu, 7 Jan 2021 03:40:42 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B71408D011F; Thu, 7 Jan 2021 03:40:42 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A878F8D0128; Thu, 7 Jan 2021 03:40:42 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0241.hostedemail.com [216.40.44.241]) by kanga.kvack.org (Postfix) with ESMTP id 9276B8D011F for ; Thu, 7 Jan 2021 03:40:42 -0500 (EST) Received: from smtpin22.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id CB25E362A for ; Thu, 7 Jan 2021 08:40:40 +0000 (UTC) X-FDA: 77678333040.22.light73_0e13ead274e8 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin22.hostedemail.com (Postfix) with ESMTP id ADD8018038E67 for ; Thu, 7 Jan 2021 08:40:40 +0000 (UTC) X-HE-Tag: light73_0e13ead274e8 X-Filterd-Recvd-Size: 4312 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf23.hostedemail.com (Postfix) with ESMTP for ; Thu, 7 Jan 2021 08:40:40 +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=1610008839; 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=rA1JsYgR7mqTecaQqhjhjqY5ZginjyT17VTN7HxEStk=; b=M2bHQmlgnooblrrxEI/FKrePrSmryUZo3N5353sQqF38Y3Jy2pTyPHEII4/pHZjEuMR19+ osbVdLOjozPAmSC+HNi9s6mled/WRbnZNV+Zuugraf18NjEs1XifCmVyzoIqNTYK0Pq+0S ANQ/aViJ3taGrlIWceX4pS+gl1B+uPk= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 1FD2BACAF; Thu, 7 Jan 2021 08:40:39 +0000 (UTC) Date: Thu, 7 Jan 2021 09:40:38 +0100 From: Michal Hocko To: Mike Kravetz Cc: Muchun Song , akpm@linux-foundation.org, n-horiguchi@ah.jp.nec.com, ak@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/6] mm: hugetlb: fix a race between freeing and dissolving the page Message-ID: <20210107084038.GC13207@dhcp22.suse.cz> References: <20210106084739.63318-1-songmuchun@bytedance.com> <20210106084739.63318-4-songmuchun@bytedance.com> <20210106165632.GT13207@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 Wed 06-01-21 12:58:29, Mike Kravetz wrote: > On 1/6/21 8:56 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? > > The tricky part with expanding lock scope will be the potential call to > hugepage_subpool_put_pages as it may also try to acquire the hugetlb_lock. Can we rearrange the code and move hugepage_subpool_put_pages after all this is done? Or is there any strong reason for the particular ordering? > I am not sure what you mean by 'check the page->lru'? If we knew the page > was on the free list, then we could dissolve. But, I do not think there > is an easy way to determine that from page->lru. A hugetlb page is either > going to be on the active list or free list. Can it be on the active list with ref count = 0? -- Michal Hocko SUSE Labs