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=-0.8 required=3.0 tests=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 4CEDAC43331 for ; Wed, 13 Nov 2019 07:53:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2FD36222C1 for ; Wed, 13 Nov 2019 07:53:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725976AbfKMHxF (ORCPT ); Wed, 13 Nov 2019 02:53:05 -0500 Received: from mout-p-201.mailbox.org ([80.241.56.171]:42486 "EHLO mout-p-201.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726074AbfKMHxE (ORCPT ); Wed, 13 Nov 2019 02:53:04 -0500 Received: from smtp1.mailbox.org (smtp1.mailbox.org [80.241.60.240]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mout-p-201.mailbox.org (Postfix) with ESMTPS id 47CcKk24kPzQlBh; Wed, 13 Nov 2019 08:52:58 +0100 (CET) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp1.mailbox.org ([80.241.60.240]) by spamfilter03.heinlein-hosting.de (spamfilter03.heinlein-hosting.de [80.241.56.117]) (amavisd-new, port 10030) with ESMTP id Bp_N38N4yiqo; Wed, 13 Nov 2019 08:52:50 +0100 (CET) Date: Wed, 13 Nov 2019 18:52:27 +1100 From: Aleksa Sarai To: Al Viro Cc: Jeff Layton , "J. Bruce Fields" , Arnd Bergmann , David Howells , Shuah Khan , Shuah Khan , Ingo Molnar , Peter Zijlstra , Christian Brauner , Jann Horn , Linus Torvalds , Eric Biederman , Andy Lutomirski , Andrew Morton , Alexei Starovoitov , Kees Cook , Tycho Andersen , David Drysdale , Chanho Min , Oleg Nesterov , Rasmus Villemoes , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Christian Brauner , Aleksa Sarai , containers@lists.linux-foundation.org, linux-alpha@vger.kernel.org, linux-api@vger.kernel.org, libc-alpha@sourceware.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org Subject: Re: [PATCH v15 6/9] namei: LOOKUP_{IN_ROOT,BENEATH}: permit limited ".." resolution Message-ID: <20191113075227.lu5b5uvc2nuk76uk@yavin.dot.cyphar.com> References: <20191105090553.6350-1-cyphar@cyphar.com> <20191105090553.6350-7-cyphar@cyphar.com> <20191113020917.GC26530@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="qprdfpbfkuvffdu5" Content-Disposition: inline In-Reply-To: <20191113020917.GC26530@ZenIV.linux.org.uk> Sender: linux-m68k-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-m68k@vger.kernel.org Message-ID: <20191113075227.Tsrt5n0sJ00ZANpsV0xEm8fdtCSKYJaALBsO4nJD-Uk@z> --qprdfpbfkuvffdu5 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-11-13, Al Viro wrote: > On Tue, Nov 05, 2019 at 08:05:50PM +1100, Aleksa Sarai wrote: >=20 > > One other possible alternative (which previous versions of this patch > > used) would be to check with path_is_under() if there was a racing > > rename or mount (after re-taking the relevant seqlocks). While this does > > work, it results in possible O(n*m) behaviour if there are many renames > > or mounts occuring *anywhere on the system*. >=20 > BTW, do you realize that open-by-fhandle (or working nfsd, for that matte= r) > will trigger arseloads of write_seqlock(&rename_lock) simply on d_splice_= alias() > bringing disconnected subtrees in contact with parent? I wasn't aware of that -- that makes path_is_under() even less viable. I'll reword it to be clearer that path_is_under() isn't a good idea and why we went with -EAGAIN over an in-kernel retry. --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --qprdfpbfkuvffdu5 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXcu2OAAKCRCdlLljIbnQ EtqZAQCjNdiANKBF7WCOTHUeD48U+o/7WczR7I/1WTsCcSBp9gEA6HgEdHKRHmol +5Fvn3Eg1Tya83fWQgWoVLu8i6CUUwE= =voMa -----END PGP SIGNATURE----- --qprdfpbfkuvffdu5--