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=-5.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 E9277C2D0E0 for ; Wed, 9 Sep 2020 20:44:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B8A4221D43 for ; Wed, 9 Sep 2020 20:44:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fieldses.org header.i=@fieldses.org header.b="tuYZxvNL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726534AbgIIUob (ORCPT ); Wed, 9 Sep 2020 16:44:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39766 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729507AbgIIUob (ORCPT ); Wed, 9 Sep 2020 16:44:31 -0400 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 30EE5C061573 for ; Wed, 9 Sep 2020 13:44:30 -0700 (PDT) Received: by fieldses.org (Postfix, from userid 2815) id 01502AB6; Wed, 9 Sep 2020 16:44:29 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org 01502AB6 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1599684270; bh=Yb4Am/ag4XbCzbjMvrocrka2QV6iC2SdZhrDf5Xug0M=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=tuYZxvNL8FEI4hdS4jyUChQJZCy3CWmexxK7ID7ZghCU0FMh9E6+tAXYc/SnSagRY YehauMoplvfzeIS7m/8QR9Dj7XFZara8dxJy3/bmsQfuD0CZmBAXXpcg4LQxBw+UOM emnZLjlmSHb2AnsaP2BE0fHoWW/0BnQYPQPI83Lc= Date: Wed, 9 Sep 2020 16:44:29 -0400 From: "J. Bruce Fields" To: Anna Schumaker Cc: "J. Bruce Fields" , Chuck Lever , Linux NFS Mailing List Subject: Re: [PATCH v5 4/5] NFSD: Return both a hole and a data segment Message-ID: <20200909204429.GD3894@fieldses.org> References: <20200908162559.509113-1-Anna.Schumaker@Netapp.com> <20200908162559.509113-5-Anna.Schumaker@Netapp.com> <20200908194944.GC6256@pick.fieldses.org> <20200909202400.GB3894@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200909202400.GB3894@fieldses.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Wed, Sep 09, 2020 at 04:24:00PM -0400, bfields wrote: > On Wed, Sep 09, 2020 at 12:51:38PM -0400, Anna Schumaker wrote: > > On Tue, Sep 8, 2020 at 3:49 PM J. Bruce Fields wrote: > > > I think there's still a race here: > > > > > > vfs_llseek(.,0,SEEK_HOLE) returns 1024 > > > read 1024 bytes of data > > > another process fills the hole > > > vfs_llseek(.,1024,SEEK_DATA) returns 1024 > > > code above returns nfserr_resource > > > > > > We end up returning an error to the client when we should have just > > > returned more data. > > > > As long as we've encoded at least one segment successfully, we'll > > actually return a short read in this case (as of the most recent > > patches). I tried implementing a check for what each segment actually > > was before encoding, but it lead to a lot of extra lseeks (so > > potential for races / performance problems on btrfs). Returning a > > short read seemed like a better approach to me. > > Argh, right, I forgot the "if (nfserr && segments == 0)" at the end of > nfsd4_encode_read_plus(). (Oops, it's actually the "if (nfserr)" below that handles that case.) > It's still possible to get a spurious error return if this happens at > the very start of the READ_PLUS, though. Hm. Might be better to just > encode another data segment? So, I mean, if nfsd4_encode_read_plus_hole() doesn't find a hole after all, just keep going, and create a data segment. --b. > > --b. > > > > > Anna > > > > > > > > --b. > > > > > > > + count = data_pos - read->rd_offset; > > > > + > > > > /* Content type, offset, byte count */ > > > > p = xdr_reserve_space(&resp->xdr, 4 + 8 + 8); > > > > if (!p) > > > > @@ -4654,9 +4662,10 @@ nfsd4_encode_read_plus_hole(struct nfsd4_compoundres *resp, > > > > > > > > *p++ = htonl(NFS4_CONTENT_HOLE); > > > > p = xdr_encode_hyper(p, read->rd_offset); > > > > - p = xdr_encode_hyper(p, maxcount); > > > > + p = xdr_encode_hyper(p, count); > > > > > > > > - *eof = (read->rd_offset + maxcount) >= i_size_read(file_inode(file)); > > > > + *eof = (read->rd_offset + count) >= i_size_read(file_inode(file)); > > > > + *maxcount = min_t(unsigned long, count, *maxcount); > > > > return nfs_ok; > > > > } > > > > > > > > @@ -4664,7 +4673,7 @@ static __be32 > > > > nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr, > > > > struct nfsd4_read *read) > > > > { > > > > - unsigned long maxcount; > > > > + unsigned long maxcount, count; > > > > struct xdr_stream *xdr = &resp->xdr; > > > > struct file *file; > > > > int starting_len = xdr->buf->len; > > > > @@ -4687,6 +4696,7 @@ nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr, > > > > maxcount = min_t(unsigned long, maxcount, > > > > (xdr->buf->buflen - xdr->buf->len)); > > > > maxcount = min_t(unsigned long, maxcount, read->rd_length); > > > > + count = maxcount; > > > > > > > > eof = read->rd_offset >= i_size_read(file_inode(file)); > > > > if (eof) > > > > @@ -4695,24 +4705,38 @@ nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr, > > > > pos = vfs_llseek(file, read->rd_offset, SEEK_DATA); > > > > if (pos == -ENXIO) > > > > pos = i_size_read(file_inode(file)); > > > > + else if (pos < 0) > > > > + pos = read->rd_offset; > > > > > > > > - if (pos > read->rd_offset) { > > > > - maxcount = pos - read->rd_offset; > > > > - nfserr = nfsd4_encode_read_plus_hole(resp, read, maxcount, &eof); > > > > + if (pos == read->rd_offset) { > > > > + maxcount = count; > > > > + nfserr = nfsd4_encode_read_plus_data(resp, read, &maxcount, &eof); > > > > + if (nfserr) > > > > + goto out; > > > > + count -= maxcount; > > > > + read->rd_offset += maxcount; > > > > segments++; > > > > - } else { > > > > - nfserr = nfsd4_encode_read_plus_data(resp, read, maxcount, &eof); > > > > + } > > > > + > > > > + if (count > 0 && !eof) { > > > > + maxcount = count; > > > > + nfserr = nfsd4_encode_read_plus_hole(resp, read, &maxcount, &eof); > > > > + if (nfserr) > > > > + goto out; > > > > + count -= maxcount; > > > > + read->rd_offset += maxcount; > > > > segments++; > > > > } > > > > > > > > out: > > > > - if (nfserr) > > > > + if (nfserr && segments == 0) > > > > xdr_truncate_encode(xdr, starting_len); > > > > else { > > > > tmp = htonl(eof); > > > > write_bytes_to_xdr_buf(xdr->buf, starting_len, &tmp, 4); > > > > tmp = htonl(segments); > > > > write_bytes_to_xdr_buf(xdr->buf, starting_len + 4, &tmp, 4); > > > > + nfserr = nfs_ok; > > > > } > > > > > > > > return nfserr; > > > > -- > > > > 2.28.0 > > > > > > >