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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2D6DFC7EE26 for ; Mon, 22 May 2023 11:41:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B664E900003; Mon, 22 May 2023 07:41:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AC76C900002; Mon, 22 May 2023 07:41:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 966FE900003; Mon, 22 May 2023 07:41:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 839E5900002 for ; Mon, 22 May 2023 07:41:52 -0400 (EDT) Received: from smtpin28.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 39D1E40DA4 for ; Mon, 22 May 2023 11:41:52 +0000 (UTC) X-FDA: 80817701664.28.5E0EE00 Received: from out-41.mta0.migadu.com (out-41.mta0.migadu.com [91.218.175.41]) by imf20.hostedemail.com (Postfix) with ESMTP id 262891C0016 for ; Mon, 22 May 2023 11:41:49 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=h991mvuT; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf20.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.41 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1684755710; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=s9cmspJubmVALzr9R4FiGgADvWy/zsxX0daTT9ez0U8=; b=Omq+GFSakDqRkwiQdR09NAbP5BsgZhV97lyNltFuOdsUbAkHUoHVXAsg45szPuYJwSKhuA qu9XRvl9H0S/YBXosNr2KGzy2nvCmkJoh1z63K+8KyU2/5Bb9+pDPrdbsUVkd7A+qZKrIR 3duHz1huf7lCWR4pUCOKIG7ko3OwbP4= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=h991mvuT; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf20.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.41 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1684755710; a=rsa-sha256; cv=none; b=AJJmueAs2rztaZJHahK/Toh41KL0LdILK3EuXwdazJeTLq5bz162evvaA2blQjwCnQK253 jNtzTS6X8zgbsiV2q9y8zIoO2vDxJbQX9I7InVt4lygBCjZ3M1mGGT5QYkys0PsQN6axea 8bKBNpmeCErUCAuFO+1baHtH3ZymMjk= Message-ID: <10e58e7e-a52e-751d-f693-cd4e05ac10ca@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1684755708; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=s9cmspJubmVALzr9R4FiGgADvWy/zsxX0daTT9ez0U8=; b=h991mvuT0dKHypdxWkkXlCCOJMdEV93/HXLbiuDCCAYWfZAEW+iIZmx2CFWeYnusaxXwiw bZgajcN3QcfG1zDR6ctnIODlf73lQXniPNoiUh5+JPuawnwzifrfYHdRSFTTAwvRID93vG a7yzyDbsTRUR7J842zzLmZCTH+r/yVk= Date: Mon, 22 May 2023 19:41:35 +0800 MIME-Version: 1.0 Subject: Re: [PATCH 08/31] mm/page_vma_mapped: pte_offset_map_nolock() not pte_lockptr() Content-Language: en-US To: Hugh Dickins , Andrew Morton Cc: Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> <8fa3fb6e-2e39-cbea-c529-ee9e64c7d2d0@google.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: <8fa3fb6e-2e39-cbea-c529-ee9e64c7d2d0@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 262891C0016 X-Stat-Signature: i3yuopg1kqk1fmhm7an5stzqqay3aft4 X-Rspam-User: X-HE-Tag: 1684755709-610550 X-HE-Meta: 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 EaE46L7G a//v2moO0DQTdFrMjKXz3dRVGkA189LPSf8KojtA4ftFu6DCS1vXyMYnmqo8GDfeDful8Hb8Idxh0NcdGVtHBfwClKZEmVH4KXHRrq/JSTN04Z8gbYHIY5YEy4UG38jq70/womjSY0T522NJv3tVukg3uhzr/XwNcKTkH 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 2023/5/22 12:58, Hugh Dickins wrote: > map_pte() use pte_offset_map_nolock(), to make sure of the ptl belonging > to pte, even if pmd entry is then changed racily: page_vma_mapped_walk() > use that instead of getting pte_lockptr() later, or restart if map_pte() > found no page table. > > Signed-off-by: Hugh Dickins > --- > mm/page_vma_mapped.c | 28 ++++++++++++++++++++++------ > 1 file changed, 22 insertions(+), 6 deletions(-) > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index 947dc7491815..2af734274073 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -13,16 +13,28 @@ static inline bool not_found(struct page_vma_mapped_walk *pvmw) > return false; > } > > -static bool map_pte(struct page_vma_mapped_walk *pvmw) > +static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp) > { > if (pvmw->flags & PVMW_SYNC) { > /* Use the stricter lookup */ > pvmw->pte = pte_offset_map_lock(pvmw->vma->vm_mm, pvmw->pmd, > pvmw->address, &pvmw->ptl); > - return true; > + *ptlp = pvmw->ptl; > + return !!pvmw->pte; > } > > - pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address); > + /* > + * It is important to return the ptl corresponding to pte, > + * in case *pvmw->pmd changes underneath us; so we need to > + * return it even when choosing not to lock, in case caller > + * proceeds to loop over next ptes, and finds a match later. > + * Though, in most cases, page lock already protects this. > + */ > + pvmw->pte = pte_offset_map_nolock(pvmw->vma->vm_mm, pvmw->pmd, > + pvmw->address, ptlp); > + if (!pvmw->pte) > + return false; > + > if (pvmw->flags & PVMW_MIGRATION) { > if (!is_swap_pte(*pvmw->pte)) > return false; > @@ -51,7 +63,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) > } else if (!pte_present(*pvmw->pte)) { > return false; > } > - pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd); > + pvmw->ptl = *ptlp; > spin_lock(pvmw->ptl); > return true; > } > @@ -156,6 +168,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > struct vm_area_struct *vma = pvmw->vma; > struct mm_struct *mm = vma->vm_mm; > unsigned long end; > + spinlock_t *ptl; > pgd_t *pgd; > p4d_t *p4d; > pud_t *pud; > @@ -257,8 +270,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > step_forward(pvmw, PMD_SIZE); > continue; > } > - if (!map_pte(pvmw)) > + if (!map_pte(pvmw, &ptl)) { > + if (!pvmw->pte) > + goto restart; Could pvmw->pmd be changed? Otherwise, how about just jumping to the retry label below? @@ -205,6 +205,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) } pvmw->pmd = pmd_offset(pud, pvmw->address); + +retry: /* * Make sure the pmd value isn't cached in a register by the * compiler and used as a stale value after we've observed a > goto next_pte; > + } > this_pte: > if (check_pte(pvmw)) > return true; > @@ -281,7 +297,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > } while (pte_none(*pvmw->pte)); > > if (!pvmw->ptl) { > - pvmw->ptl = pte_lockptr(mm, pvmw->pmd); > + pvmw->ptl = ptl; > spin_lock(pvmw->ptl); > } > goto this_pte; -- Thanks, Qi