From nobody Tue Feb 10 22:15:53 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 707C5C7EE23 for ; Mon, 22 May 2023 05:06:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231714AbjEVFGl (ORCPT ); Mon, 22 May 2023 01:06:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48864 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229722AbjEVFGi (ORCPT ); Mon, 22 May 2023 01:06:38 -0400 Received: from mail-yw1-x112b.google.com (mail-yw1-x112b.google.com [IPv6:2607:f8b0:4864:20::112b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F330A92 for ; Sun, 21 May 2023 22:06:36 -0700 (PDT) Received: by mail-yw1-x112b.google.com with SMTP id 00721157ae682-561bcd35117so70100797b3.3 for ; Sun, 21 May 2023 22:06:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1684731996; x=1687323996; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to; bh=itm4lMYCv8hAr7oWbErSKKsiGUM8mghvSpbiblkFfbk=; b=xUO60/u0hCL36TvKXHyURnnxqO5vn7ZybjY7ONPqMVFmXcRaGi5WJ1fjIK85dRtVJa +whV5tpXJtxlVEd0xUGkv7xuykXYLwzIAtD/A83Pd0ByM1utIbe7HqhKdkTngJ8uTZye nXdCtHMDNgLl+HSpG2o6gWxk89SbFvj51bDmDs5EUuxNtQO799f4KEwsfMDYpb1aA0JV G1qpsPEAFFQ60/jP3AFkOagxrcttoK3mZdLQdFsbhRCY1FyAsYOWEizdcI6h50IGdllG JcD8IVUHEVvPfu5cztMQwnxIE3n4xO4E81T6/znW0rbNwJzdKCpC1q5F2RM6c3EnqDt5 BYMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1684731996; x=1687323996; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=itm4lMYCv8hAr7oWbErSKKsiGUM8mghvSpbiblkFfbk=; b=JGede4ErEdyjhrVGGycNcFkSlUzDrvCtgqWU0mr2ngN1RWwWkpuG7SwIm9NmseuFLm 3A8tm2hbTSo59diT3g4riGqiQQXsv99qZ6pSNVGejltHyDcspDTDMXwE9ZBaKGdqhmiJ q+wfrWRCje9E9i2Ajz1CeEj/wCp2m+ufJ/A2/VwJLeFrYvZWJ7puGzz0FkFGmk99b7Ki +f/amxmJncen/f2z0D9nFl1cCUw1fGOKdPnx6b29OyqHiKGpX5y46aoKz7pgrqNrzVee USvVE5a0x2q8Lf+emynG6xHaTetF2VkRWOLdXyG1i9oygMjXOPUNDp5u+4dptyjebj7o 9rqQ== X-Gm-Message-State: AC+VfDyWEanvfquZs+woCunWTjm387zYd+Wrl8dX1Ux5wQZRyOpSTP0e 6PZUZ4KCWi18UwXbKwNd72IEIQ== X-Google-Smtp-Source: ACHHUZ78QIP2SjKpIXnCqaoasaQ8h+cR3FlbUtT2N1GVyk/3dI0nRSCd0E3wxVyacPDSOVPhhCpzYw== X-Received: by 2002:a0d:ed43:0:b0:561:9d6e:6f45 with SMTP id w64-20020a0ded43000000b005619d6e6f45mr10989561ywe.26.1684731996077; Sun, 21 May 2023 22:06:36 -0700 (PDT) Received: from ripple.attlocal.net (172-10-233-147.lightspeed.sntcca.sbcglobal.net. [172.10.233.147]) by smtp.gmail.com with ESMTPSA id v184-20020a8148c1000000b0054f50f71834sm1805106ywa.124.2023.05.21.22.06.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 21 May 2023 22:06:35 -0700 (PDT) Date: Sun, 21 May 2023 22:06:32 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: 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 Subject: [PATCH 14/31] fs/userfaultfd: retry if pte_offset_map() fails In-Reply-To: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> Message-ID: <424274a4-7c13-e14-b380-428fc69a45c5@google.com> References: <68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Instead of worrying whether the pmd is stable, userfaultfd_must_wait() call pte_offset_map() as before, but go back to try again if that fails. Risk of endless loop? It already broke out if pmd_none(), !pmd_present() or pmd_trans_huge(), and pte_offset_map() would have cleared pmd_bad(): which leaves pmd_devmap(). Presumably pmd_devmap() is inappropriate in a vma subject to userfaultfd (it would have been mistreated before), but add a check just to avoid all possibility of endless loop there. Signed-off-by: Hugh Dickins Acked-by: Peter Xu --- fs/userfaultfd.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index f7a0817b1ec0..ca83423f8d54 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -349,12 +349,13 @@ static inline bool userfaultfd_must_wait(struct userf= aultfd_ctx *ctx, if (!pud_present(*pud)) goto out; pmd =3D pmd_offset(pud, address); +again: _pmd =3D pmdp_get_lockless(pmd); if (pmd_none(_pmd)) goto out; =20 ret =3D false; - if (!pmd_present(_pmd)) + if (!pmd_present(_pmd) || pmd_devmap(_pmd)) goto out; =20 if (pmd_trans_huge(_pmd)) { @@ -363,11 +364,11 @@ static inline bool userfaultfd_must_wait(struct userf= aultfd_ctx *ctx, goto out; } =20 - /* - * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it - * and use the standard pte_offset_map() instead of parsing _pmd. - */ pte =3D pte_offset_map(pmd, address); + if (!pte) { + ret =3D true; + goto again; + } /* * Lockless access: we're in a wait_event so it's ok if it * changes under us. PTE markers should be handled the same as none --=20 2.35.3