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![Darrick J. Wong](/assets/img/avatar_default.png)
As part of testing log recovery with dm_log_writes, Amir Goldstein discovered an error in the deferred ops recovery that lead to corruption of the filesystem metadata if a reflink+rmap filesystem happened to shut down midway through a CoW remap: "This is what happens [after failed log recovery]: "Phase 1 - find and verify superblock... "Phase 2 - using internal log " - zero log... " - scan filesystem freespace and inode maps... " - found root inode chunk "Phase 3 - for each AG... " - scan (but don't clear) agi unlinked lists... " - process known inodes and perform inode discovery... " - agno = 0 "data fork in regular inode 134 claims CoW block 376 "correcting nextents for inode 134 "bad data fork in inode 134 "would have cleared inode 134" Hou Tao dissected the log contents of exactly such a crash: "According to the implementation of xfs_defer_finish(), these ops should be completed in the following sequence: "Have been done: "(1) CUI: Oper (160) "(2) BUI: Oper (161) "(3) CUD: Oper (194), for CUI Oper (160) "(4) RUI A: Oper (197), free rmap [0x155, 2, -9] "Should be done: "(5) BUD: for BUI Oper (161) "(6) RUI B: add rmap [0x155, 2, 137] "(7) RUD: for RUI A "(8) RUD: for RUI B "Actually be done by xlog_recover_process_intents() "(5) BUD: for BUI Oper (161) "(6) RUI B: add rmap [0x155, 2, 137] "(7) RUD: for RUI B "(8) RUD: for RUI A "So the rmap entry [0x155, 2, -9] for COW should be freed firstly, then a new rmap entry [0x155, 2, 137] will be added. However, as we can see from the log record in post_mount.log (generated after umount) and the trace print, the new rmap entry [0x155, 2, 137] are added firstly, then the rmap entry [0x155, 2, -9] are freed." When reconstructing the internal log state from the log items found on disk, it's required that deferred ops replay in exactly the same order that they would have had the filesystem not gone down. However, replaying unfinished deferred ops can create /more/ deferred ops. These new deferred ops are finished in the wrong order. This causes fs corruption and replay crashes, so let's create a single defer_ops to handle the subsequent ops created during replay, then use one single transaction at the end of log recovery to ensure that everything is replayed in the same order as they're supposed to be. Reported-by: Amir Goldstein <amir73il@gmail.com> Analyzed-by: Hou Tao <houtao1@huawei.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Tested-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
99 lines
3.3 KiB
C
99 lines
3.3 KiB
C
/*
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* Copyright (C) 2016 Oracle. All Rights Reserved.
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*
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* Author: Darrick J. Wong <darrick.wong@oracle.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it would be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#ifndef __XFS_BMAP_ITEM_H__
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#define __XFS_BMAP_ITEM_H__
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/*
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* There are (currently) two pairs of bmap btree redo item types: map & unmap.
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* The common abbreviations for these are BUI (bmap update intent) and BUD
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* (bmap update done). The redo item type is encoded in the flags field of
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* each xfs_map_extent.
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*
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* *I items should be recorded in the *first* of a series of rolled
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* transactions, and the *D items should be recorded in the same transaction
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* that records the associated bmbt updates.
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*
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* Should the system crash after the commit of the first transaction but
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* before the commit of the final transaction in a series, log recovery will
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* use the redo information recorded by the intent items to replay the
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* bmbt metadata updates in the non-first transaction.
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*/
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/* kernel only BUI/BUD definitions */
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struct xfs_mount;
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struct kmem_zone;
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/*
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* Max number of extents in fast allocation path.
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*/
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#define XFS_BUI_MAX_FAST_EXTENTS 1
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/*
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* Define BUI flag bits. Manipulated by set/clear/test_bit operators.
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*/
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#define XFS_BUI_RECOVERED 1
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/*
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* This is the "bmap update intent" log item. It is used to log the fact that
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* some reverse mappings need to change. It is used in conjunction with the
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* "bmap update done" log item described below.
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*
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* These log items follow the same rules as struct xfs_efi_log_item; see the
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* comments about that structure (in xfs_extfree_item.h) for more details.
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*/
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struct xfs_bui_log_item {
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struct xfs_log_item bui_item;
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atomic_t bui_refcount;
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atomic_t bui_next_extent;
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unsigned long bui_flags; /* misc flags */
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struct xfs_bui_log_format bui_format;
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};
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static inline size_t
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xfs_bui_log_item_sizeof(
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unsigned int nr)
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{
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return offsetof(struct xfs_bui_log_item, bui_format) +
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xfs_bui_log_format_sizeof(nr);
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}
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/*
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* This is the "bmap update done" log item. It is used to log the fact that
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* some bmbt updates mentioned in an earlier bui item have been performed.
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*/
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struct xfs_bud_log_item {
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struct xfs_log_item bud_item;
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struct xfs_bui_log_item *bud_buip;
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struct xfs_bud_log_format bud_format;
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};
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extern struct kmem_zone *xfs_bui_zone;
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extern struct kmem_zone *xfs_bud_zone;
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struct xfs_bui_log_item *xfs_bui_init(struct xfs_mount *);
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struct xfs_bud_log_item *xfs_bud_init(struct xfs_mount *,
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struct xfs_bui_log_item *);
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void xfs_bui_item_free(struct xfs_bui_log_item *);
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void xfs_bui_release(struct xfs_bui_log_item *);
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int xfs_bui_recover(struct xfs_mount *mp, struct xfs_bui_log_item *buip,
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struct xfs_defer_ops *dfops);
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#endif /* __XFS_BMAP_ITEM_H__ */
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