Btrfs devel - Nov 2013 - Partition broken, btrfsck segfaults or asserts

Hello!

I have a serious problem with inaccessible data and segfaulting btrfsck
for the /var partition on my computer.

The reason is not entirely clear to me. The only extraordinary things
happening today were an empty CMOS battery and me accidentally enabling
C1E support when reconfiguring the BIOS. Afterwards the computer did
not boot properly anymore (some GPU lockup thingy and the whole system
locked up hard before X would start) and when I cut the power and setup
the BIOS again (this time without C1E support), /var would be broken in
the state I describe below.

I can mount it, and dmesg says the following, which seems normal:
---
device label var devid 1 transid 393536 /dev/sda7
btrfs: use lzo compression
btrfs: enabling auto defrag
---

When I access certain directories, however, I get a message like this
one:
ls: cannot access /var/log: Stale NFS file handle

When I run btrfsck --repair it asserts, and when I just run btrfsck
without extra options it segfaults. Sadly I do not have debug symbols
installed, so the backtrace is probably useless. I attached the
stdout/err output of both runs to the bugzilla report:
https://bugzilla.kernel.org/show_bug.cgi?id=64411

# btrfs --version
Btrfs v0.20-rc1-358-g194aa4a

# uname -r
3.11.6-gentoo

I would be thankful if you could help me to get as much as possible of
my data back. And please CC me, as I am not subscribed to the list.

Best regards,
Dennis

P.S: I already sent an email yesterday, but it did not arrive in the
archives, so I assume it was blocked by the list for the two ~125kB
attachments.

Dennis Schridde posted on Tue, 05 Nov 2013 13:04:59 +0100 as excerpted:
> I have a serious problem with inaccessible data and segfaulting btrfsck
> for the /var partition on my computer.
> I can mount it[.] When I access certain directories, however, I get a
> message like this one:
> ls: cannot access /var/log: Stale NFS file handle
> When I run btrfsck --repair it asserts, and when I just run btrfsck
> without extra options it segfaults.
Ouch!
> https://bugzilla.kernel.org/show_bug.cgi?id=64411
> 
> # btrfs --version Btrfs v0.20-rc1-358-g194aa4a
> 
> # uname -r 3.11.6-gentoo
Fellow gentooer, and quite upto date both kernel- and tools-wise, as 
befits a still experimental filesystem under heavy development.

=:^)
> I would be thankful if you could help me to get as much as possible of
> my data back. And please CC me, as I am not subscribed to the list.
Posted directly to you and to list as requested.

Unfortunately I don''t have an easy guaranteed recovery solution.

But since you''re running an experimental filesystem that both the btrfs
wiki (mentioned in the gentoo btrfs-tools package post-inst message) and 
the kernel config option warn to keep tested backups and use only with 
non-critical data, either restore from that tested backup or by 
definition you considered the data not critical enough to be worth 
worrying about recovering if it was lost in the first place.  Thus no 
worries either way.  Either you had tested backups and can restore from 
them, or by your actions you already declared the data not worth worrying 
about if the still experimental filesystem ate it for lunch!

Meanwhile, I see you''ve tried a few recovery methods, but it might be 
worth mentioning this post, with a list of methods to try and in what 
order:

http://permalink.gmane.org/gmane.comp.file-systems.btrfs/27999

And in case you missed the gentoo btrfs-tools package homepage link, 
which is to the wiki, here it is again.  If you haven''t already,
it''s
worth reading up. =:^)

https://btrfs.wiki.kernel.org

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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