btrfs check error: btrfs_reserve_extent: Assertion `ret` failed.

btrfs check error: btrfs_reserve_extent: Assertion `ret` failed.

[Bryan Olmstead]

I'll try and keep this short, so if you would like anymore information
please let me know.  This is a 5 disk raid5 mdadm array used for
offsite backup.  There is no backup of it, it is the backup.  :)  I
would just like to save it if possible since it takes quite a long to
time to do the initial backup if it ends up lost.

root@nas:/home/olmstead/tempwatch# btrfs fi show
Label: none  uuid: eb0fcdf0-f8be-4d8d-9c62-02b1b01c2642
        Total devices 1 FS bytes used 1.94TiB
        devid    1 size 2.73TiB used 2.09TiB path /dev/mapper/md0

btrfs-progs v4.3

root@nas:~/scripts/raid# uname -a
Linux nas 4.1.12 #1 SMP PREEMPT Sun Nov 8 11:49:53 PST 2015 x86_64 AMD
Phenom(tm) 9600 Quad-Core Processor AuthenticAMD GNU/Linux


After a few days of trying to figure out why the kernel kept oopsing
(and it didn't appear to be btrfs related) and much searching I found
out that some ram had gone bad.  After fixing this I started to try
and fix the problems I'd found that had developed in the btrfs fs I
have.  At first it was many uncorrectable crc errors (reported by
btrfs check and btrfs scrub).  After much seraching and running the
various utilities I found a thread that talked about what the various
repair/check/fix commands do and in order of use:

  https://mail-archive.com/linux-btrfs%40vger.kernel.org/msg37929.html

I ran these again from top down and am at the point of:

root@nas:~/scripts/raid# btrfs check --repair --init-csum-tree
--init-extent-tree /dev/mapper/md0
enabling repair mode
Creating a new CRC tree
Checking filesystem on /dev/mapper/md0
UUID: eb0fcdf0-f8be-4d8d-9c62-02b1b01c2642
Creating a new extent tree
Failed to find [1407100010496, 168, 16384]
btrfs unable to find ref byte nr 1407100010496 parent 0 root 1  owner 1 offset 0
Failed to find [1572461953024, 168, 16384]
btrfs unable to find ref byte nr 1572461953024 parent 0 root 1  owner 0 offset 1
parent transid verify failed on 29442048 wanted 4 found 41583
Ignoring transid failure
Reinit crc root
extent-tree.c:2694: btrfs_reserve_extent: Assertion `ret` failed.
btrfs[0x442081]
btrfs(btrfs_reserve_extent+0xb88)[0x447879]
btrfs(btrfs_alloc_free_block+0x57)[0x447921]
btrfs[0x43a864]
btrfs(btrfs_search_slot+0x1334)[0x43c72b]
btrfs(btrfs_csum_file_block+0x352)[0x44c5a4]
btrfs[0x41c4dd]
btrfs(cmd_check+0x119c)[0x429bb8]
btrfs(main+0x155)[0x40a3b9]
/lib64/libc.so.6(__libc_start_main+0xf5)[0x7f1a3136fea5]
btrfs[0x409f19]

Thank you in advance,

Bryan