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=-17.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,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 2F39FC4361B for ; Mon, 14 Dec 2020 10:23:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B92BA22B48 for ; Mon, 14 Dec 2020 10:23:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406040AbgLNKWq (ORCPT ); Mon, 14 Dec 2020 05:22:46 -0500 Received: from mx2.suse.de ([195.135.220.15]:57844 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729460AbgLNKW1 (ORCPT ); Mon, 14 Dec 2020 05:22:27 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1607941300; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=5mpblBlhQ7TbmbydSdwgPbUrHHxMjHJLyUjKbRXdLUE=; b=Cv29VZkBCbxZh+DQxQEai/WVxinTd7NWArD22fD0cw2BK2H8OCZb1xgCW3W8F/qyG7fJ42 BzWwj3K79qvg7yXyZ7o1i77/3wmSI3c4i60LfBh3r33i4+hRiGvjd0oV7Ef8DJl8Ahk3Vd d7kxhWjFnJl5nW7rgIUWPnS2BlRHjHg= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 85AF5AC90; Mon, 14 Dec 2020 10:21:40 +0000 (UTC) Subject: Re: [PATCH v2 15/18] btrfs: disk-io: introduce subpage metadata validation check To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20201210063905.75727-1-wqu@suse.com> <20201210063905.75727-16-wqu@suse.com> From: Nikolay Borisov Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= mQINBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/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/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABtCNOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuY29tPokCOAQTAQIAIgUCWIo48QIbAwYLCQgHAwIGFQgC CQoLBBYCAwECHgECF4AACgkQcb6CRuU/KFc0eg/9GLD3wTQz9iZHMFbjiqTCitD7B6dTLV1C ddZVlC8Hm/TophPts1bWZORAmYIihHHI1EIF19+bfIr46pvfTu0yFrJDLOADMDH+Ufzsfy2v HSqqWV/nOSWGXzh8bgg/ncLwrIdEwBQBN9SDS6aqsglagvwFD91UCg/TshLlRxD5BOnuzfzI Leyx2c6YmH7Oa1R4MX9Jo79SaKwdHt2yRN3SochVtxCyafDlZsE/efp21pMiaK1HoCOZTBp5 VzrIP85GATh18pN7YR9CuPxxN0V6IzT7IlhS4Jgj0NXh6vi1DlmKspr+FOevu4RVXqqcNTSS E2rycB2v6cttH21UUdu/0FtMBKh+rv8+yD49FxMYnTi1jwVzr208vDdRU2v7Ij/TxYt/v4O8 V+jNRKy5Fevca/1xroQBICXsNoFLr10X5IjmhAhqIH8Atpz/89ItS3+HWuE4BHB6RRLM0gy8 T7rN6ja+KegOGikp/VTwBlszhvfLhyoyjXI44Tf3oLSFM+8+qG3B7MNBHOt60CQlMkq0fGXd mm4xENl/SSeHsiomdveeq7cNGpHi6i6ntZK33XJLwvyf00PD7tip/GUj0Dic/ZUsoPSTF/mG EpuQiUZs8X2xjK/AS/l3wa4Kz2tlcOKSKpIpna7V1+CMNkNzaCOlbv7QwprAerKYywPCoOSC 7P25Ag0EWIoHPgEQAMiUqvRBZNvPvki34O/dcTodvLSyOmK/MMBDrzN8Cnk302XfnGlW/YAQ csMWISKKSpStc6tmD+2Y0z9WjyRqFr3EGfH1RXSv9Z1vmfPzU42jsdZn667UxrRcVQXUgoKg QYx055Q2FdUeaZSaivoIBD9WtJq/66UPXRRr4H/+Y5FaUZx+gWNGmBT6a0S/GQnHb9g3nonD jmDKGw+YO4P6aEMxyy3k9PstaoiyBXnzQASzdOi39BgWQuZfIQjN0aW+Dm8kOAfT5i/yk59h VV6v3NLHBjHVw9kHli3jwvsizIX9X2W8tb1SefaVxqvqO1132AO8V9CbE1DcVT8fzICvGi42 FoV/k0QOGwq+LmLf0t04Q0csEl+h69ZcqeBSQcIMm/Ir+NorfCr6HjrB6lW7giBkQl6hhomn l1mtDP6MTdbyYzEiBFcwQD4terc7S/8ELRRybWQHQp7sxQM/Lnuhs77MgY/e6c5AVWnMKd/z MKm4ru7A8+8gdHeydrRQSWDaVbfy3Hup0Ia76J9FaolnjB8YLUOJPdhI2vbvNCQ2ipxw3Y3c KhVIpGYqwdvFIiz0Fej7wnJICIrpJs/+XLQHyqcmERn3s/iWwBpeogrx2Lf8AGezqnv9woq7 OSoWlwXDJiUdaqPEB/HmGfqoRRN20jx+OOvuaBMPAPb+aKJyle8zABEBAAGJAh8EGAECAAkF AliKBz4CGwwACgkQcb6CRuU/KFdacg/+M3V3Ti9JYZEiIyVhqs+yHb6NMI1R0kkAmzsGQ1jU zSQUz9AVMR6T7v2fIETTT/f5Oout0+Hi9cY8uLpk8CWno9V9eR/B7Ifs2pAA8lh2nW43FFwp IDiSuDbH6oTLmiGCB206IvSuaQCp1fed8U6yuqGFcnf0ZpJm/sILG2ECdFK9RYnMIaeqlNQm iZicBY2lmlYFBEaMXHoy+K7nbOuizPWdUKoKHq+tmZ3iA+qL5s6Qlm4trH28/fPpFuOmgP8P K+7LpYLNSl1oQUr+WlqilPAuLcCo5Vdl7M7VFLMq4xxY/dY99aZx0ZJQYFx0w/6UkbDdFLzN upT7NIN68lZRucImffiWyN7CjH23X3Tni8bS9ubo7OON68NbPz1YIaYaHmnVQCjDyDXkQoKC R82Vf9mf5slj0Vlpf+/Wpsv/TH8X32ajva37oEQTkWNMsDxyw3aPSps6MaMafcN7k60y2Wk/ TCiLsRHFfMHFY6/lq/c0ZdOsGjgpIK0G0z6et9YU6MaPuKwNY4kBdjPNBwHreucrQVUdqRRm RcxmGC6ohvpqVGfhT48ZPZKZEWM+tZky0mO7bhZYxMXyVjBn4EoNTsXy1et9Y1dU3HVJ8fod 5UqrNrzIQFbdeM0/JqSLrtlTcXKJ7cYFa9ZM2AP7UIN9n1UWxq+OPY9YMOewVfYtL8M= Message-ID: Date: Mon, 14 Dec 2020 12:21:39 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201210063905.75727-16-wqu@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 10.12.20 г. 8:39 ч., Qu Wenruo wrote: > For subpage metadata validation check, there are some difference: > - Read must finish in one bvec > Since we're just reading one subpage range in one page, it should > never be split into two bios nor two bvecs. > > - How to grab the existing eb > Instead of grabbing eb using page->private, we have to go search radix > tree as we don't have any direct pointer at hand. > > Signed-off-by: Qu Wenruo > --- > fs/btrfs/disk-io.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 82 insertions(+) > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index b6c03a8b0c72..adda76895058 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -591,6 +591,84 @@ static int validate_extent_buffer(struct extent_buffer *eb) > return ret; > } > > +static int validate_subpage_buffer(struct page *page, u64 start, u64 end, > + int mirror) > +{ > + struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb); > + struct extent_buffer *eb; > + int reads_done; > + int ret = 0; > + > + if (!IS_ALIGNED(start, fs_info->sectorsize) || That's guaranteed by the allocator. > + !IS_ALIGNED(end - start + 1, fs_info->sectorsize) || That's guaranteed by the fact that nodesize is a multiple of sectorsize. > + !IS_ALIGNED(end - start + 1, fs_info->nodesize)) { And that's also guaranteed that the size of an eb is always a nodesize. Also aren't those checks already performed by the tree-checker during write? Just remove this as it adds noise. > + WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));> + btrfs_err(fs_info, "invalid tree read bytenr"); > + return -EUCLEAN; > + } > + > + /* > + * We don't allow bio merge for subpage metadata read, so we should > + * only get one eb for each endio hook. > + */ > + ASSERT(end == start + fs_info->nodesize - 1); > + ASSERT(PagePrivate(page)); > + > + rcu_read_lock(); > + eb = radix_tree_lookup(&fs_info->buffer_radix, > + start / fs_info->sectorsize); This division op likely produces the kernel robot's warning. It could be written to use >> fs_info->sectorsize_bits. Furthermore this usage of radix tree + rcu without acquiring the refs is unsafe as per my explanation of, essentially, identical issue in patch 12 and our offline chat about it. > + rcu_read_unlock(); > + > + /* > + * When we are reading one tree block, eb must have been > + * inserted into the radix tree. If not something is wrong. > + */ > + if (!eb) { > + WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG)); > + btrfs_err(fs_info, > + "can't find extent buffer for bytenr %llu", > + start); > + return -EUCLEAN; > + } That's impossible to execute and such a failure will result in a crash so just remove this code. > + /* > + * The pending IO might have been the only thing that kept > + * this buffer in memory. Make sure we have a ref for all > + * this other checks > + */ > + atomic_inc(&eb->refs); > + > + reads_done = atomic_dec_and_test(&eb->io_pages); > + /* Subpage read must finish in page read */ > + ASSERT(reads_done); Just ASSERT(atomic_dec_and_test(&eb->io_pages)). Again, for subpage I think that's a bit much since it only has 1 page so it's guaranteed that it will always be true. > + > + eb->read_mirror = mirror; > + if (test_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags)) { > + ret = -EIO; > + goto err; > + } > + ret = validate_extent_buffer(eb); > + if (ret < 0) > + goto err; > + > + if (test_and_clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) > + btree_readahead_hook(eb, ret); > + > + set_extent_buffer_uptodate(eb); > + > + free_extent_buffer(eb); > + return ret; > +err: > + /* > + * our io error hook is going to dec the io pages > + * again, we have to make sure it has something to > + * decrement > + */ That comment is slightly ambiguous - it's not the io error hook that does the decrement but end_bio_extent_readpage. Just rewrite the comment to : "end_bio_extent_readpage decrements io_pages in case of error, make sure it has ...." > + atomic_inc(&eb->io_pages); > + clear_extent_buffer_uptodate(eb); > + free_extent_buffer(eb); > + return ret; > +} > + > int btrfs_validate_metadata_buffer(struct btrfs_io_bio *io_bio, > struct page *page, u64 start, u64 end, > int mirror) > @@ -600,6 +678,10 @@ int btrfs_validate_metadata_buffer(struct btrfs_io_bio *io_bio, > int reads_done; > > ASSERT(page->private); > + > + if (btrfs_sb(page->mapping->host->i_sb)->sectorsize < PAGE_SIZE) > + return validate_subpage_buffer(page, start, end, mirror); nit: validate_metadata_buffer is called in only once place so I'm wondering won't it make it more readable if this check is lifted to its sole caller so that when reading end_bio_extent_readpage it's apparent what's going on. Though it's apparent that the nesting in the caller will get somewhat unwieldy so won't be pressing hard for this. > + > eb = (struct extent_buffer *)page->private; > > >