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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 965AFC34024 for ; Mon, 17 Feb 2020 14:13:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6EE062072C for ; Mon, 17 Feb 2020 14:13:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728102AbgBQONw (ORCPT ); Mon, 17 Feb 2020 09:13:52 -0500 Received: from mx2.suse.de ([195.135.220.15]:50178 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727132AbgBQONw (ORCPT ); Mon, 17 Feb 2020 09:13:52 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 7CCF0B32A; Mon, 17 Feb 2020 14:13:49 +0000 (UTC) Subject: Re: [PATCH v3 2/3] btrfs: backref: Implement btrfs_backref_iterator_next() To: Qu Wenruo , Qu Wenruo , linux-btrfs@vger.kernel.org References: <20200217063111.65941-1-wqu@suse.com> <20200217063111.65941-3-wqu@suse.com> <2cee1b97-b6a3-bffd-8cb0-cb7d903497ca@gmx.com> <696547c7-84ea-d346-cecb-6270c2430031@suse.com> <3aadef5b-7bd2-b830-869f-67de417a4600@gmx.com> From: Nikolay Borisov Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= xsFNBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/nSSP8YgfwoOqwrP+JR4pIqRK0AWWeWCSwmZ T7g+RbfPFlmQp+EwFWOtABXlKC54zgSf+uulGwx5JAUFVUIRBmnHOYi/lUiE0yhpnb1KCA7f u/W+DkwGerXqhhe9TvQoGwgCKNfzFPZoM+gZrm+kWv03QLUCr210n4cwaCPJ0Nr9Z3c582xc bCUVbsjt7BN0CFa2BByulrx5xD9sDAYIqfLCcZetAqsTRGxM7LD0kh5WlKzOeAXj5r8DOrU2 GdZS33uKZI/kZJZVytSmZpswDsKhnGzRN1BANGP8sC+WD4eRXajOmNh2HL4P+meO1TlM3GLl EQd2shHFY0qjEo7wxKZI1RyZZ5AgJnSmehrPCyuIyVY210CbMaIKHUIsTqRgY5GaNME24w7h TyyVCy2qAM8fLJ4Vw5bycM/u5xfWm7gyTb9V1TkZ3o1MTrEsrcqFiRrBY94Rs0oQkZvunqia c+NprYSaOG1Cta14o94eMH271Kka/reEwSZkC7T+o9hZ4zi2CcLcY0DXj0qdId7vUKSJjEep c++s8ncFekh1MPhkOgNj8pk17OAESanmDwksmzh1j12lgA5lTFPrJeRNu6/isC2zyZhTwMWs k3LkcTa8ZXxh0RfWAqgx/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABzSJOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuZGU+wsF4BBMBAgAiBQJYijkSAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAAKCRBxvoJG5T8oV/B6D/9a8EcRPdHg8uLEPywuJR8URwXzkofT5bZE IfGF0Z+Lt2ADe+nLOXrwKsamhweUFAvwEUxxnndovRLPOpWerTOAl47lxad08080jXnGfYFS Dc+ew7C3SFI4tFFHln8Y22Q9075saZ2yQS1ywJy+TFPADIprAZXnPbbbNbGtJLoq0LTiESnD w/SUC6sfikYwGRS94Dc9qO4nWyEvBK3Ql8NkoY0Sjky3B0vL572Gq0ytILDDGYuZVo4alUs8 LeXS5ukoZIw1QYXVstDJQnYjFxYgoQ5uGVi4t7FsFM/6ykYDzbIPNOx49Rbh9W4uKsLVhTzG BDTzdvX4ARl9La2kCQIjjWRg+XGuBM5rxT/NaTS78PXjhqWNYlGc5OhO0l8e5DIS2tXwYMDY LuHYNkkpMFksBslldvNttSNei7xr5VwjVqW4vASk2Aak5AleXZS+xIq2FADPS/XSgIaepyTV tkfnyreep1pk09cjfXY4A7qpEFwazCRZg9LLvYVc2M2eFQHDMtXsH59nOMstXx2OtNMcx5p8 0a5FHXE/HoXz3p9bD0uIUq6p04VYOHsMasHqHPbsMAq9V2OCytJQPWwe46bBjYZCOwG0+x58 fBFreP/NiJNeTQPOa6FoxLOLXMuVtpbcXIqKQDoEte9aMpoj9L24f60G4q+pL/54ql2VRscK d87BTQRYigc+ARAAyJSq9EFk28++SLfg791xOh28tLI6Yr8wwEOvM3wKeTfTZd+caVb9gBBy wxYhIopKlK1zq2YP7ZjTP1aPJGoWvcQZ8fVFdK/1nW+Z8/NTjaOx1mfrrtTGtFxVBdSCgqBB jHTnlDYV1R5plJqK+ggEP1a0mr/rpQ9dFGvgf/5jkVpRnH6BY0aYFPprRL8ZCcdv2DeeicOO YMobD5g7g/poQzHLLeT0+y1qiLIFefNABLN06Lf0GBZC5l8hCM3Rpb4ObyQ4B9PmL/KTn2FV Xq/c0scGMdXD2QeWLePC+yLMhf1fZby1vVJ59pXGq+o7XXfYA7xX0JsTUNxVPx/MgK8aLjYW hX+TRA4bCr4uYt/S3ThDRywSX6Hr1lyp4FJBwgyb8iv42it8KvoeOsHqVbuCIGRCXqGGiaeX Wa0M/oxN1vJjMSIEVzBAPi16tztL/wQtFHJtZAdCnuzFAz8ue6GzvsyBj97pzkBVacwp3/Mw qbiu7sDz7yB0d7J2tFBJYNpVt/Lce6nQhrvon0VqiWeMHxgtQ4k92Eja9u80JDaKnHDdjdwq FUikZirB28UiLPQV6PvCckgIiukmz/5ctAfKpyYRGfez+JbAGl6iCvHYt/wAZ7Oqe/3Cirs5 KhaXBcMmJR1qo8QH8eYZ+qhFE3bSPH446+5oEw8A9v5oonKV7zMAEQEAAcLBXwQYAQIACQUC WIoHPgIbDAAKCRBxvoJG5T8oV1pyD/4zdXdOL0lhkSIjJWGqz7Idvo0wjVHSSQCbOwZDWNTN JBTP0BUxHpPu/Z8gRNNP9/k6i63T4eL1xjy4umTwJaej1X15H8Hsh+zakADyWHadbjcUXCkg OJK4NsfqhMuaIYIHbToi9K5pAKnV953xTrK6oYVyd/Rmkmb+wgsbYQJ0Ur1Ficwhp6qU1CaJ mJwFjaWaVgUERoxcejL4ruds66LM9Z1Qqgoer62ZneID6ovmzpCWbi2sfbz98+kW46aA/w8r 7sulgs1KXWhBSv5aWqKU8C4twKjlV2XsztUUsyrjHFj91j31pnHRklBgXHTD/pSRsN0UvM26 lPs0g3ryVlG5wiZ9+JbI3sKMfbdfdOeLxtL25ujs443rw1s/PVghphoeadVAKMPINeRCgoJH zZV/2Z/myWPRWWl/79amy/9MfxffZqO9rfugRBORY0ywPHLDdo9Kmzoxoxp9w3uTrTLZaT9M KIuxEcV8wcVjr+Wr9zRl06waOCkgrQbTPp631hToxo+4rA1jiQF2M80HAet65ytBVR2pFGZF zGYYLqiG+mpUZ+FPjxk9kpkRYz61mTLSY7tuFljExfJWMGfgSg1OxfLV631jV1TcdUnx+h3l Sqs2vMhAVt14zT8mpIuu2VNxcontxgVr1kzYA/tQg32fVRbGr449j1gw57BV9i0vww== Message-ID: Date: Mon, 17 Feb 2020 16:13:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <3aadef5b-7bd2-b830-869f-67de417a4600@gmx.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 17.02.20 г. 13:45 ч., Qu Wenruo wrote: > > > On 2020/2/17 下午7:42, Nikolay Borisov wrote: >> >> >> On 17.02.20 г. 13:29 ч., Qu Wenruo wrote: >>> >>> >>> On 2020/2/17 下午6:47, Nikolay Borisov wrote: >>>> >>>> >>>> On 17.02.20 г. 8:31 ч., Qu Wenruo wrote: >>>>> This function will go next inline/keyed backref for >>>>> btrfs_backref_iterator infrastructure. >>>>> >>>>> Signed-off-by: Qu Wenruo >>>>> --- >>>>> fs/btrfs/backref.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++ >>>>> fs/btrfs/backref.h | 34 +++++++++++++++++++++++++++++++++ >>>>> 2 files changed, 81 insertions(+) >>>>> >>>>> diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c >>>>> index 8bd5e067831c..fb0abe344851 100644 >>>>> --- a/fs/btrfs/backref.c >>>>> +++ b/fs/btrfs/backref.c >>>>> @@ -2310,3 +2310,50 @@ int btrfs_backref_iterator_start(struct btrfs_backref_iterator *iterator, >>>>> btrfs_backref_iterator_release(iterator); >>>>> return ret; >>>>> } >>>>> + >>>>> +int btrfs_backref_iterator_next(struct btrfs_backref_iterator *iterator) >>>> >>>> Document the return values: 0 in case there are more backerfs for the >>>> given bytenr or 1 in case there are'nt. And a negative value in case of >>>> error. >>>> >>>>> +{ >>>>> + struct extent_buffer *eb = btrfs_backref_get_eb(iterator); >>>>> + struct btrfs_path *path = iterator->path; >>>>> + struct btrfs_extent_inline_ref *iref; >>>>> + int ret; >>>>> + u32 size; >>>>> + >>>>> + if (btrfs_backref_iterator_is_inline_ref(iterator)) { >>>>> + /* We're still inside the inline refs */ >>>>> + if (btrfs_backref_has_tree_block_info(iterator)) { >>>>> + /* First tree block info */ >>>>> + size = sizeof(struct btrfs_tree_block_info); >>>>> + } else { >>>>> + /* Use inline ref type to determine the size */ >>>>> + int type; >>>>> + >>>>> + iref = (struct btrfs_extent_inline_ref *) >>>>> + (iterator->cur_ptr); >>>>> + type = btrfs_extent_inline_ref_type(eb, iref); >>>>> + >>>>> + size = btrfs_extent_inline_ref_size(type); >>>>> + } >>>>> + iterator->cur_ptr += size; >>>>> + if (iterator->cur_ptr < iterator->end_ptr) >>>>> + return 0; >>>>> + >>>>> + /* All inline items iterated, fall through */ >>>>> + } >>>> >>>> This if could be rewritten as: >>>> if (btrfs_backref_iterator_is_inline_ref(iterator) && iterator->cur_ptr >>>> < iterator->end_ptr) >>>> >>>> what this achieves is: >>>> >>>> 1. Clarity that this whole branch is executed only if we are within the >>>> inline refs limits >>>> 2. It also optimises that function since in the current version, after >>>> the last inline backref has been processed iterator->cur_ptr == >>>> iterator->end_ptr. On the next call to btrfs_backref_iterator_next you >>>> will execute (needlessly) >>>> >>>> (struct btrfs_extent_inline_ref *) (iterator->cur_ptr); >>>> type = btrfs_extent_inline_ref_type(eb, iref); >>>> size = btrfs_extent_inline_ref_size(type); >>>> iterator->cur_ptr += size; >>>> only to fail "if (iterator->cur_ptr < iterator->end_ptr)" check and >>>> continue processing keyed items. >>>> >>>> As a matter of fact you will be reading past the metadata_item since >>>> cur_ptr will be at the end of them and any deferences will read from the >>>> next item this might not cause a crash but it's still wrong. >>> >>> This shouldn't happen, as we must ensure the cur_ptr < item_end for callers. >> >> >> How are you ensuring this? Before processing the last inline ref >> cur_ptr would be end_ptr - btrfs_extent_inline_ref_size(type); > > Firstly, in _start() call, we can easily check if we have any inline refs. > > If no, search next item. > If yes, return cur_ptr which points to the current inline extent ref. > > Secondly, in _next() call, we keep current check. Increase cur_ptr, then > check against ptr_end. > > So that, all backref_iter callers will get a cur_ptr that is always > smaller than ptr_end. Apparently not, btrfs/003 with the following assert: diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c index fb0abe344851..403a75f0c99c 100644 --- a/fs/btrfs/backref.c +++ b/fs/btrfs/backref.c @@ -2328,6 +2328,7 @@ int btrfs_backref_iterator_next(struct btrfs_backref_iterator *iterator) /* Use inline ref type to determine the size */ int type; + ASSERT(iterator->cur_ptr < iterator->end_ptr); iref = (struct btrfs_extent_inline_ref *) (iterator->cur_ptr); type = btrfs_extent_inline_ref_type(eb, iref); Trigger: [ 58.884441] assertion failed: iterator->cur_ptr < iterator->end_ptr, in fs/btrfs/backref.c:2331 > > Thanks, > Qu >> >> After it's processed cur_ptr == end_ptr. THen you will do another call >> to btrfs_backref_iterator_next which will do the same calculation? What >> am I missing? >> >>> >>> For the _next() call, the check after increased cur_ptr check it's OK. >>> >>> But it's a problem for _start() call, as we may have a case where an >>> EXTENT_ITEM/METADATA_ITEM has no inlined ref. >>> >>> I'll fix this in next version. >>> >>> Thanks, >>> Qu >>> >>>> >>>> >>>>> + /* We're at keyed items, there is no inline item, just go next item */ >>>>> + ret = btrfs_next_item(iterator->fs_info->extent_root, iterator->path); >>>>> + if (ret > 0 || ret < 0) >>>>> + return ret; >>>> >>>> nit: if (ret != 0) return ret; >>>> >>>> >>>>