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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 17E30C6FA83 for ; Sat, 10 Sep 2022 22:13:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230007AbiIJWNe (ORCPT ); Sat, 10 Sep 2022 18:13:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56140 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229965AbiIJWNc (ORCPT ); Sat, 10 Sep 2022 18:13:32 -0400 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [IPv6:2a03:a000:7:0:5054:ff:fe1c:15ff]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16CB565E3 for ; Sat, 10 Sep 2022 15:13:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=YR+ntuHl5fOk06kmMtEESyE6d9xq40oR2msXPof/X2w=; b=GYfnMrOwmiEwokZy0Qh/lHe7aQ tbI9wJ0z/ENTAX8UtsRkMpjm6+0lEx+hvtd1jSo+S8hTUhN+mKPo/UaxtUfOca1sMQc4R8WeoB/mb q0ZlxBmPTZl7QcML/WdP9I1A+aFA/AB+g15JWYCu1ZkNYhv9Ps6Y4vygxyMOojNxubFf3T53qARKI ccpKozpFomaGX2cGzHglUXbDkjH/5BV8/YY65p0p78Y+CYy9/lq/EfEi05FC4qta8Lu4xKCJq2eVV Q7wH6QgRQz5AoB9QMPxGKO87P7/dBiAVEbB8e0KdauIt7g0dZXQrkui7nVgqA+rcnS01pf6P1RXDp 1JsOiAlw==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.95 #2 (Red Hat Linux)) id 1oX8is-00ESF7-Ar; Sat, 10 Sep 2022 22:13:10 +0000 Date: Sat, 10 Sep 2022 23:13:10 +0100 From: Al Viro To: Chuck Lever III Cc: Benjamin Coddington , Olga Kornievskaia , Jeff Layton , Linux NFS Mailing List Subject: Re: Is this nfsd kernel oops known? Message-ID: References: <5c423fdf25e6cedb2dcdbb9c8665d6a9ab4ad4b1.camel@kernel.org> <11BEA7FE-4CBC-4E5C-9B68-A0310CF1F3BE@oracle.com> <25AF9743-A2A2-4AFE-9123-BAD3C8F17655@redhat.com> <9D6CDF68-6B12-44DE-BC01-3BD0251E7F94@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9D6CDF68-6B12-44DE-BC01-3BD0251E7F94@oracle.com> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Sat, Sep 10, 2022 at 09:21:11PM +0000, Chuck Lever III wrote: > It's also possible that recent simplifications I've done to the splice > read actor accidentally removed the ability to deal with compound pages. > You might want to review the commit history of nfsd_splice_actor() to > see if there is an historic version that would behave correctly with > the new copy_page_to_iter(). Nah, that's unrelated... > Is the need to deal with CompoundPage documented somewhere? If not, > perhaps nfsd_splice_actor() could mention it so that overzealous > maintainers don't break it again. > > + struct page *page = buf->page; // may be a compound one Does that qualify? ;-) FWIW, there's a separate problem in that thing - it assumes that pipe_buffer boundaries will end up PAGE_SIZE-aligned. Usually that's going to be true, but foofs_splice_read() is not required to maintain that. E.g. it might be working in terms of chunks used by weird protocol used by foofs, with e.g. 1024-byte payloads + 300-odd bytes of framing/checskums/whatnot. In that case it might do 1024 bytes per pipe_buffer, with non-zero offset in page in each of them; normal read()/splice()/etc. would work just fine with that, but for nfsd_splice_actor() results would not be nice. AFAICS, sunrpc assumes that we have several pages, offset in the first one and total size; no provisions exist for e.g. 5Kb of data scattered in 5 chunks over 5 pages. Correct?