Comment 6 for bug 1774794

FWIW, it looks like btrfs-convert is being dropped upstream. I just compiled mine from source, and it crashed after some heavy churning. The package description should be changed though (it explicitly mentions btrfs-convert). Here's a relevant thread:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=854489

referring to the note in https://btrfs.wiki.kernel.org/index.php/Conversion_from_Ext3:

“Warning: As of 4.0 kernels this feature is not often used or well tested anymore, and there have been some reports that the conversion doesn't work reliably. Feel free to try it out, but make sure you have backups.”

My backtrace was different, but also related to btrfs_reserve_extent(). I also attempted ext4 -> btrfs. I'll post the BT but it's hardly helpful:

# btrfs-convert /dev/sdc1
create btrfs filesystem:
        blocksize: 4096
        nodesize: 16384
        features: extref, skinny-metadata (default)
creating ext2 image file
Unable to find block group for 0
Unable to find block group for 0
Unable to find block group for 0
extent-tree.c:2764: alloc_tree_block: BUG_ON `ret` triggered, value -28
btrfs-convert(+0x1c4f6)[0x558cfb6c54f6]
btrfs-convert(btrfs_alloc_free_block+0x1ff)[0x558cfb6cabaf]
btrfs-convert(+0x14d63)[0x558cfb6bdd63]
btrfs-convert(btrfs_search_slot+0x2af)[0x558cfb6bec8f]
btrfs-convert(btrfs_csum_file_block+0x48f)[0x558cfb6d0c1f]
btrfs-convert(+0xd944)[0x558cfb6b6944]
btrfs-convert(main+0x19d1)[0x558cfb6b5df1]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7)[0x7f75d48fcb97]
btrfs-convert(_start+0x2a)[0x558cfb6b64da]
Aborted