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Thu, 21 Feb 2019 15:01:32 +0000 (UTC) Subject: Re: [RFC PATCH] btrfs: Introduce developer-oriented check to ensure all tree blocks are written back before writing super blocks To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20190221082249.24187-1-wqu@suse.com> From: Nikolay Borisov Openpgp: preference=signencrypt 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: <61c89a50-bb8f-6be4-a32e-2d8d3b0cf76a@suse.com> Date: Thu, 21 Feb 2019 17:01:31 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: 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 21.02.19 г. 16:32 ч., Qu Wenruo wrote: > > > On 2019/2/21 下午10:25, Nikolay Borisov wrote: >> >> >> On 21.02.19 г. 10:22 ч., Qu Wenruo wrote: >>> There are a lot of error reports complaining about transid error in the >>> mail list. >>> >>> Under most case, the on-disk transid is lower than expected transid. >>> This may indicate that some tree blocks are not written back to disk >>> before writing super blocks. >>> >>> This patch will add a safe net for developers, by calling >>> btrfs_write_and_wait_transaction() before setting transaction unblocked >>> and double check btree_inode and dirty_pages io_tree, to ensure no tree >>> blocks are still dirty or under writeback. >>> >>> Signed-off-by: Qu Wenruo >>> --- >>> The reason for RFC is, I'm not sure why we currently call >>> btrfs_write_and_wait_transaction() after setting transaction UNBLOCKED. >>> >>> It looks like an optimization, but I don't see much performance >>> difference during regression test. >>> >>> I hope to move the call before we unblock transaction so we can do such >>> sanity check for all builds and hope to catch some clue of transid >>> error. >> >> Even current code ensures that all allocated blocks in the current >> transaction (which is what all those EXTENT_DIRTY extents in the >> dirty_pages tree ) are written before the new superblocks are. >> >> Slight offtopic: In fact instead of playing games with the flags and >> having an extent_io_tree called dirty_pages o_O it can be replaced with >> a simple linked list that holds all newly allocated buffers so writing >> all such buffers will result in simply iterating the list. >> >> In any case this patch is buggy, see below on why >> >>> --- >>> fs/btrfs/transaction.c | 38 ++++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 38 insertions(+) >>> >>> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c >>> index 4ec2b660d014..30b7ed0bf873 100644 >>> --- a/fs/btrfs/transaction.c >>> +++ b/fs/btrfs/transaction.c >>> @@ -2213,6 +2213,44 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans) >>> >>> btrfs_trans_release_chunk_metadata(trans); >>> >>> + /* Last safenet or developer to catch any unwritten tree blocks */ >>> + if (IS_ENABLED(CONFIG_BTRFS_DEBUG)) { >>> + u64 found_start = 0; >>> + u64 found_end = 0; >>> + >>> + ret = btrfs_write_and_wait_transaction(trans); >>> + if (ret) { >>> + btrfs_handle_fs_error(fs_info, ret, >>> + "Error while writing out transaction"); >>> + mutex_unlock(&fs_info->tree_log_mutex); >>> + goto scrub_continue; >>> + } >>> + >>> + /* No dirty extent should exist in btree inode */ >>> + ret = test_range_bit(&trans->transaction->dirty_pages, 0, >>> + (u64)-1, EXTENT_DIRTY | EXTENT_WRITEBACK, >> >> Why do you check EXTENT_WRITEBACK, AFAICS that flag is not currently >> used in the code and should perhahps be deleted? I don't see anything >> setting it, it's only being checked for (as part of EXTENT_IOBITS). >> >> Additionally this check is pointless because >> btrfs_write_and_wait_transaction calls clear_btree_io_tree which purges >> the tree. > > But we still have BTRFS_I(fs_info->btree_inode)->io_tree, and that's the > main part of the check. Okay, but the ->dirty_pages code is pointless. Also checking for EXTENT_WRITEBACK on the io_tree is also pointless. > > I don't really think the dirty_pages is really an important thing > compared to btree_inode. > If there is some way to find any dirty pages from an address_space, it > would be even better. > > Thanks, > Qu > >> >>> + 0, NULL); >>> + if (ret > 0) { >>> + WARN(1, >>> + "dirty_pages not fully written back, start=%llu len=%llu\n", >>> + found_start, found_end + 1 - found_start); >>> + ret = -EUCLEAN; >>> + mutex_unlock(&fs_info->tree_log_mutex); >>> + goto scrub_continue; >>> + } >>> + ret = test_range_bit(&BTRFS_I(fs_info->btree_inode)->io_tree, 0, >>> + (u64)-1, EXTENT_DIRTY | EXTENT_WRITEBACK, >>> + 0, NULL); >>> + if (ret > 0) { >>> + WARN(1, >>> + "btree io_tree not fully written back, start=%llu len=%llu\n", >>> + found_start, found_end + 1 - found_start); >>> + ret = -EUCLEAN; >>> + mutex_unlock(&fs_info->tree_log_mutex); >>> + goto scrub_continue; >>> + } >>> + } >>> + >>> spin_lock(&fs_info->trans_lock); >>> cur_trans->state = TRANS_STATE_UNBLOCKED; >>> fs_info->running_transaction = NULL; >>> >