[PATCH] xfs: ensure submit buffers on LSN boundaries in error handlers

Long Li
2023-12-28T12:50:53Z

While performing the IO fault injection test, I caught the following data
corruption report:

XFS (dm-0): Internal error ltbno + ltlen > bno at line 1957 of file fs/xfs/libxfs/xfs_alloc.c. Caller xfs_free_ag_extent+0x79c/0x1130
CPU: 3 PID: 33 Comm: kworker/3:0 Not tainted 6.5.0-rc7-next-20230825-00001-g7f8666926889 #214
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
Workqueue: xfs-inodegc/dm-0 xfs_inodegc_worker
Call Trace:
<TASK>
dump_stack_lvl+0x50/0x70
xfs_corruption_error+0x134/0x150
xfs_free_ag_extent+0x7d3/0x1130
__xfs_free_extent+0x201/0x3c0
xfs_trans_free_extent+0x29b/0xa10
xfs_extent_free_finish_item+0x2a/0xb0
xfs_defer_finish_noroll+0x8d1/0x1b40
xfs_defer_finish+0x21/0x200
xfs_itruncate_extents_flags+0x1cb/0x650
xfs_free_eofblocks+0x18f/0x250
xfs_inactive+0x485/0x570
xfs_inodegc_worker+0x207/0x530
process_scheduled_works+0x24a/0xe10
worker_thread+0x5ac/0xc60
kthread+0x2cd/0x3c0
ret_from_fork+0x4a/0x80
ret_from_fork_asm+0x11/0x20
</TASK>
XFS (dm-0): Corruption detected. Unmount and run xfs_repair

After analyzing the disk image, it was found that the corruption was
triggered by the fact that extent was recorded in both the inode and AGF
btrees. After a long time of reproduction and analysis, we found that the
root cause of the problem was that the AGF btree block was not recovered.

Consider the following situation, Transaction A and Transaction B are in
the same record, so Transaction A and Transaction B share the same LSN1.
If the buf item in Transaction A has been recovered, then the buf item in
Transaction B cannot be recovered, because log recovery skips items with a
metadata LSN >= the current LSN of the recovery item. If there is still an
inode item in transaction B that records the Extent X, the Extent X will
be recorded in both the inode and the AGF btree block after transaction B
is recovered.

|------------Record (LSN1)------------------|---Record (LSN2)---|
|----------Trans A------------|-------------Trans B-------------|
| Buf Item(Extent X) | Buf Item / Inode item(Extent X) |
| Extent X is freed | Extent X is allocated |

After commit 12818d24db8a ("xfs: rework log recovery to submit buffers on
LSN boundaries") was introduced, we submit buffers on lsn boundaries during
log recovery. The above problem can be avoided under normal paths, but it's
not guaranteed under abnormal paths. Consider the following process, if an
error was encountered after recover buf item in transaction A and before
recover buf item in transaction B, buffers that have been added to
buffer_list will still be submitted, this violates the submits rule on lsn
boundaries. So buf item in Transaction B cannot be recovered on the next
mount due to current lsn of transaction equal to metadata lsn on disk.

xlog_do_recovery_pass
error = xlog_recover_process
xlog_recover_process_data
...
xlog_recover_buf_commit_pass2
xlog_recover_do_reg_buffer //recover buf item in Trans A
xfs_buf_delwri_queue(bp, buffer_list)
...
====> Encountered error and returned
...
xlog_recover_buf_commit_pass2
xlog_recover_do_reg_buffer //recover buf item in Trans B
xfs_buf_delwri_queue(bp, buffer_list)
if (!list_empty(&buffer_list))
xfs_buf_delwri_submit(&buffer_list); //submit regardless of error

In order to make sure that submits buffers on lsn boundaries in the
abnormal paths, we need to check error status before submit buffers that
have been added from the last record processed. If error status exist,
buffers in the bufffer_list should be canceled.

Canceling the buffers in the buffer_list directly isn't correct, unlike
any other place where write list was canceled, these buffers has been
initialized by xfs_buf_item_init() during recovery and held by buf
item, buf items will not be released in xfs_buf_delwri_cancel(). If
these buffers are submitted successfully, buf items assocated with
the buffer will be released in io end process. So releasing buf item
in write list cacneling process is needed.

Fixes: 50d5c8d8e938 ("xfs: check LSN ordering for v5 superblocks during recovery")
Signed-off-by: Long Li <leo.lilong@huawei.com>
---
fs/xfs/xfs_buf.c | 2 ++
fs/xfs/xfs_log_recover.c | 22 +++++++++++++---------
2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 8e5bd50d29fe..6a1b26aaf97e 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -2075,6 +2075,8 @@ xfs_buf_delwri_cancel(
xfs_buf_lock(bp);
bp->b_flags &= ~_XBF_DELWRI_Q;
xfs_buf_list_del(bp);
+ if (bp->b_log_item)
+ xfs_buf_item_relse(bp);
xfs_buf_relse(bp);
}
}
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 1251c81e55f9..2cda6c90890d 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -2964,7 +2964,6 @@ xlog_do_recovery_pass(
char *offset;
char *hbp, *dbp;
int error = 0, h_size, h_len;
- int error2 = 0;
int bblks, split_bblks;
int hblks, split_hblks, wrapped_hblks;
int i;
@@ -3203,16 +3202,21 @@ xlog_do_recovery_pass(
bread_err1:
kmem_free(hbp);

- /*
- * Submit buffers that have been added from the last record processed,
- * regardless of error status.
- */
- if (!list_empty(&buffer_list))
- error2 = xfs_buf_delwri_submit(&buffer_list);
-
if (error && first_bad)
*first_bad = rhead_blk;

+ /*
+ * If there are no error, submit buffers that have been added from the
+ * last record processed, othrewise cancel the write list, to ensure
+ * submit buffers on LSN boundaries.
+ */
+ if (!list_empty(&buffer_list)) {
+ if (error)
+ xfs_buf_delwri_cancel(&buffer_list);
+ else
+ error = xfs_buf_delwri_submit(&buffer_list);
+ }
+
/*
* Transactions are freed at commit time but transactions without commit
* records on disk are never committed. Free any that may be left in the
@@ -3226,7 +3230,7 @@ xlog_do_recovery_pass(
xlog_recover_free_trans(trans);
}

- return error ? error : error2;
+ return error;
}

/*
--
2.31.1