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=-3.8 required=3.0 tests=BAYES_00, 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 E2CFCC47080 for ; Mon, 31 May 2021 17:45:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA2D661108 for ; Mon, 31 May 2021 17:45:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232398AbhEaRqt (ORCPT ); Mon, 31 May 2021 13:46:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58088 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233401AbhEaRq3 (ORCPT ); Mon, 31 May 2021 13:46:29 -0400 Received: from zeniv-ca.linux.org.uk (zeniv-ca.linux.org.uk [IPv6:2607:5300:60:148a::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 88E4CC0612A3 for ; Mon, 31 May 2021 10:12:36 -0700 (PDT) Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1lnlSp-0032Lo-CH; Mon, 31 May 2021 17:12:31 +0000 Date: Mon, 31 May 2021 17:12:31 +0000 From: Al Viro To: Andreas Gruenbacher Cc: Linus Torvalds , cluster-devel@redhat.com, linux-kernel@vger.kernel.org, Jan Kara , Matthew Wilcox Subject: Re: [RFC 5/9] iov_iter: Add iov_iter_fault_in_writeable() Message-ID: References: <20210531170123.243771-1-agruenba@redhat.com> <20210531170123.243771-6-agruenba@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210531170123.243771-6-agruenba@redhat.com> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 31, 2021 at 07:01:19PM +0200, Andreas Gruenbacher wrote: > Add the equivalent of iov_iter_fault_in_readable(), but for pages that > will be written to. > > While at it, fix an indentation error in iov_iter_fault_in_readable(). > +int iov_iter_fault_in_writeable(struct iov_iter *i, size_t bytes) > +{ > + size_t skip = i->iov_offset; > + const struct iovec *iov; > + int err; > + struct iovec v; > + > + if (!(i->type & (ITER_BVEC|ITER_KVEC))) { > + iterate_iovec(i, bytes, v, iov, skip, ({ > + err = fault_in_pages_writeable(v.iov_base, v.iov_len); > + if (unlikely(err)) > + return err; > + 0;})) > + } > + return 0; > +} > +EXPORT_SYMBOL(iov_iter_fault_in_writeable); I really don't like that. Conflicts with iov_iter patches are not hard to deal with, but (like fault_in_pages_writeable() itself) it's dangerous as hell - fault-in for read is non-destructive, but that is *not*. Existing users have to be careful with it and there are very few of those. Adding that as a new primitive is inviting trouble; at the very least it needs a big fat "Don't use unless you really know what you are doing" kind of warning. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Date: Mon, 31 May 2021 17:12:31 +0000 Subject: [Cluster-devel] [RFC 5/9] iov_iter: Add iov_iter_fault_in_writeable() In-Reply-To: <20210531170123.243771-6-agruenba@redhat.com> References: <20210531170123.243771-1-agruenba@redhat.com> <20210531170123.243771-6-agruenba@redhat.com> Message-ID: List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Mon, May 31, 2021 at 07:01:19PM +0200, Andreas Gruenbacher wrote: > Add the equivalent of iov_iter_fault_in_readable(), but for pages that > will be written to. > > While at it, fix an indentation error in iov_iter_fault_in_readable(). > +int iov_iter_fault_in_writeable(struct iov_iter *i, size_t bytes) > +{ > + size_t skip = i->iov_offset; > + const struct iovec *iov; > + int err; > + struct iovec v; > + > + if (!(i->type & (ITER_BVEC|ITER_KVEC))) { > + iterate_iovec(i, bytes, v, iov, skip, ({ > + err = fault_in_pages_writeable(v.iov_base, v.iov_len); > + if (unlikely(err)) > + return err; > + 0;})) > + } > + return 0; > +} > +EXPORT_SYMBOL(iov_iter_fault_in_writeable); I really don't like that. Conflicts with iov_iter patches are not hard to deal with, but (like fault_in_pages_writeable() itself) it's dangerous as hell - fault-in for read is non-destructive, but that is *not*. Existing users have to be careful with it and there are very few of those. Adding that as a new primitive is inviting trouble; at the very least it needs a big fat "Don't use unless you really know what you are doing" kind of warning.