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 E4774C433B4 for ; Mon, 26 Apr 2021 18:54:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A97976023E for ; Mon, 26 Apr 2021 18:54:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234481AbhDZSzd (ORCPT ); Mon, 26 Apr 2021 14:55:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50130 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240656AbhDZSy6 (ORCPT ); Mon, 26 Apr 2021 14:54:58 -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 7754AC061574; Mon, 26 Apr 2021 11:54:16 -0700 (PDT) Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94 #2 (Red Hat Linux)) id 1lb6N2-008TLy-M3; Mon, 26 Apr 2021 18:54:12 +0000 Date: Mon, 26 Apr 2021 18:54:12 +0000 From: Al Viro To: David Howells Cc: linux-fsdevel@vger.kernel.org, Dave Wysochanski , Marc Dionne , "Matthew Wilcox (Oracle)" , Christoph Hellwig , linux-mm@kvack.org, linux-cachefs@redhat.com, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Jeff Layton , linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 01/31] iov_iter: Add ITER_XARRAY Message-ID: References: <161918446704.3145707.14418606303992174310.stgit@warthog.procyon.org.uk> <161918448151.3145707.11541538916600921083.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <161918448151.3145707.11541538916600921083.stgit@warthog.procyon.org.uk> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org On Fri, Apr 23, 2021 at 02:28:01PM +0100, David Howells wrote: > -#define iterate_all_kinds(i, n, v, I, B, K) { \ > +#define iterate_xarray(i, n, __v, skip, STEP) { \ > + struct page *head = NULL; \ > + size_t wanted = n, seg, offset; \ > + loff_t start = i->xarray_start + skip; \ > + pgoff_t index = start >> PAGE_SHIFT; \ > + int j; \ > + \ > + XA_STATE(xas, i->xarray, index); \ > + \ > + rcu_read_lock(); \ > + xas_for_each(&xas, head, ULONG_MAX) { \ > + if (xas_retry(&xas, head)) \ > + continue; \ OK, now I'm really confused; what's to guarantee that restart will not have you hit the same entry more than once? STEP might be e.g. memcpy_to_page(v.bv_page, v.bv_offset, (from += v.bv_len) - v.bv_len, v.bv_len) which is clearly not idempotent - from gets incremented, after all. What am I missing here? > + if (WARN_ON(xa_is_value(head))) \ > + break; \ > + if (WARN_ON(PageHuge(head))) \ > + break; \ > + for (j = (head->index < index) ? index - head->index : 0; \ > + j < thp_nr_pages(head); j++) { \ > + __v.bv_page = head + j; \ > + offset = (i->xarray_start + skip) & ~PAGE_MASK; \ > + seg = PAGE_SIZE - offset; \ > + __v.bv_offset = offset; \ > + __v.bv_len = min(n, seg); \ > + (void)(STEP); \ > + n -= __v.bv_len; \ > + skip += __v.bv_len; \ > + if (n == 0) \ > + break; \ > + } \ > + if (n == 0) \ > + break; \ > + } \ > + rcu_read_unlock(); \ > + n = wanted - n; \ > +}