On Fri, Mar 29, 2024 at 10:55:29AM +0800, Stephen Zhang wrote:
> Hi all,
>
> It's all about the commit 09654ed8a18c ("xfs: check sb_meta_uuid for
> dabuf buffer recovery").
>
> IIUC, any XFS buffer will be in an internally consistent state
> regardless of whether any other buffer is replaying to it.
>
> Specifically, for a buffer like:
>
> ...
> bleaf[0].hashval = 0x2e
> bleaf[0].address = 0x8
> bleaf[1].hashval = 0x172e
> bleaf[1].address = 0xa
> bleaf[2].hashval = 0x4eccc517
> bleaf[2].address = 0x36
> bleaf[3].hashval = 0x4eccc519
> bleaf[3].address = 0x2a
> bleaf[4].hashval = 0x4eccc51a
> bleaf[4].address = 0x24
> bleaf[5].hashval = 0x4eccc51b
> bleaf[5].address = 0x1e
> bleaf[6].hashval = 0x4eccc51e
> bleaf[6].address = 0xc
> bleaf[7].hashval = 0x9133c702
> bleaf[7].address = 0x68
> bleaf[8].hashval = 0x9133c704
> bleaf[8].address = 0x52
> bleaf[9].hashval = 0x9133c705
> bleaf[9].address = 0
> bleaf[10].hashval = 0x9133c706
> bleaf[10].address = 0x3c
> bleaf[11].hashval = 0x9133c707
> bleaf[11].address = 0
> btail.count = 12
> btail.stale = 2
>
> and then If we skip a buffer replay during log recovery, the buffer
> will still be in an internally consistent state. This implies that the
> 'stale' or 'count' will be consistent with the real count in the
> block, meaning it won't trigger the check in xfs_dir3_leaf_check_int.
>
> but the commit 09654ed8a18c ("xfs: check sb_meta_uuid for dabuf buffer
> recovery") states that in some scenarios, IIUC, if we skip a buffer
> replay during log recovery, the buffer will not be in an internally
> consistent state.
>
> What could cause this inconsistency? Are there any potential issues
> with the directory block?
Original state: count = 12, stale = 2
Change A: adds entry @ 12
count = 13, stale = 2
Change B: removes entry 4
count = 13, stale = 3
Change C; adds entry @ 9
count = 13, stale = 2
So at the end of recovering these individual changes, we have stale
entries at 4 and 11.
Now let's fail to replay Change B. What's the final state when we
replay only A + C over the original buffer? Is it internally
consistent?
However, log recovery should never allow this "silently fail to
recover intermediate change" situation to occur - if it can't
recover change B, it must abort recovery immediately and never
attempt to recover change C....
-Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
