On 2020/9/30 上午9:44, Eric Levy wrote:
> I recently upgraded a Linux system running on btrfs from a 5.3.x
> kernel to a 5.4.x version. The system failed to run for more than a
> few minutes after the upgrade, because the root mount degraded to a
> read-only state. I continued to use the system by booting using the
> 5.3.x kernel.

Dmesg please. But according to your btrfs check result, I think it's
already caused by bad extent generation from older kernels.

> 
> Some time later, I attempted to migrate the root subvolume using a
> send-receive command pairing, and noticed that the operation would
> invariably abort before completion. I also noticed that a full file
> walk of the mounted volume was impossible, because operations on some
> files generated errors from the file-system level.
> 
> Upon investigating using a check command, I learned that the file
> system had errors.
> 
> Examining the error report (not saved), I noticed that overall my
> situation had rather clear similarities to one described in an earlier
> discussion [1].
> 
> Unfortunately, it appears that the differences in the kernels may have
> corrupted the file system.

Nope, your fs is still fine.

> 
> Based on eagerness for a resolution, and on an optimistic comment
> toward the end of the discussion, I chose to run a check operation on
> the partition with the --repair flag included.

And obviously it won't help. Since we don't have extent item repair
functionality yet.

There is an off-tree branch to do the repair:
https://github.com/adam900710/btrfs-progs/tree/extent_gen_repair

You could try that to see if it works.

Thanks,
Qu

> 
> Perhaps not surprisingly to some, the result of a read-only check
> operation after the attempted repair gave a much more discouraging
> report, suggesting that the damage to the file system was made worse
> not better by the operation. I realize that this possibility is
> explained in the documentation.
> 
> At the moment, the full report appears as below.
> 
> Presently, the file system mounts, but the ability to successfully
> read files degrades the longer the system is mounted and the more
> files are read during a continuous mount. Experiments involving
> unmounting and then mounting again give some indication that this
> degradation is not entirely permanent.
> 
> What possibility is open to recover all or part of the file system?
> After such a rescue attempt, would I have any way to know what is lost
> versus saved? Might I expect corruption within the file contents that
> would not be detected by the rescue effort?
> 
> I would be thankful for any guidance that might lead to restoring the data
> 
> 
> [1] https://www.spinics.net/lists/linux-btrfs/msg96735.html
> ---
> 
> Opening filesystem to check...
> Checking filesystem on /dev/sda5
> UUID: 9a4da0b6-7e39-4a5f-85eb-74acd11f5b94
> [1/7] checking root items
> [2/7] checking extents
> ERROR: invalid generation for extent 4064026624, have 94810718697136
> expect (0, 33469925]
> ERROR: invalid generation for extent 16323178496, have 94811372174048
> expect (0, 33469925]
> ERROR: invalid generation for extent 79980945408, have 94811372219744
> expect (0, 33469925]
> ERROR: invalid generation for extent 318963990528, have 94810111593504
> expect (0, 33469925]
> ERROR: invalid generation for extent 319650189312, have 14758526976
> expect (0, 33469925]
> ERROR: invalid generation for extent 319677259776, have 414943019007
> expect (0, 33469925]
> ERROR: errors found in extent allocation tree or chunk allocation
> [3/7] checking free space cache
> block group 71962722304 has wrong amount of free space, free space
> cache has 266420224 block group has 266354688
> ERROR: free space cache has more free space than block group item,
> this could leads to serious corruption, please contact btrfs
> developers
> failed to load free space cache for block group 71962722304
> [4/7] checking fs roots
> [5/7] checking only csums items (without verifying data)
> [6/7] checking root refs
> [7/7] checking quota groups
> found 399845548032 bytes used, error(s) found
> total csum bytes: 349626220
> total tree bytes: 5908873216
> total fs tree bytes: 4414324736
> total extent tree bytes: 879493120
> btree space waste bytes: 1122882578
> file data blocks allocated: 550505705472
>  referenced 512080416768
>