btrfs-send -c fails: reproduction case

[Zachary Vance <za3k@xxxxxxxx>]

Reproduction case after running into the same problem as Paride Legovini: http://article.gmane.org/gmane.comp.file-systems.btrfs/48706/match=send

To recap, the basic problem is that you can get into a state where "btrfs-send -c" fails for a subvolume, with "ERROR: parent determination failed for 9622".

I'm pretty sure this isn't the intended behavior, and it's certainly preventing me from copying my backups right now. If someone could confirm on a **completely** fresh system I'd appreciate it.

[root@burn ~]# sudo btrfs sub create m
Create subvolume './m'
[root@burn ~]# sudo btrfs sub create m/a
Create subvolume 'm/a'
[root@burn ~]# sudo btrfs sub create m/b
Create subvolume 'm/b'
[root@burn ~]# sudo btrfs sub snapshot m/a -r a
Create a readonly snapshot of 'm/a' in './a'
[root@burn ~]# sudo btrfs sub snapshot m/b -r b
Create a readonly snapshot of 'm/b' in './b'
[root@burn ~]# sudo btrfs sub delete m/a
Delete subvolume (no-commit): '/root/m/a'
[root@burn ~]# sudo btrfs sub delete m/b
Delete subvolume (no-commit): '/root/m/b'
[root@burn ~]# sudo btrfs sub delete m
Delete subvolume (no-commit): '/root/m'
[root@burn ~]# sudo btrfs send -c a b >/dev/null
At subvol b
ERROR: parent determination failed for 9622

[root@burn ~]# sudo btrfs subvolume show a
/root/a
        Name:                   a
        UUID:                   c86cbbb0-9dea-cf43-809d-637c57dc7e65
        Parent UUID:            bbad9a60-b418-3b46-93f5-84b8ac62adf6
        Received UUID:          -
        Creation time:          2016-02-19 08:31:47 -0800
        Subvolume ID:           9622
        Generation:             18121
        Gen at creation:        18121
        Parent ID:              5
        Top level ID:           5
        Flags:                  readonly
        Snapshot(s):

[root@burn ~]# sudo btrfs subvolume show b
/root/b
        Name:                   b
        UUID:                   bb9256c1-4fb4-ee4e-b072-0ee570521d06
        Parent UUID:            c5890f1a-94f0-ac48-a69d-656f8e0b7fc6
        Received UUID:          -
        Creation time:          2016-02-19 08:31:49 -0800
        Subvolume ID:           9623
        Generation:             18122
        Gen at creation:        18122
        Parent ID:              5
        Top level ID:           5
        Flags:                  readonly
        Snapshot(s):

[root@burn ~]# btrfs --version
btrfs-progs v4.4.1

[root@burn ~]# uname -a
Linux burn 4.5.0-1-ARCH #1 SMP PREEMPT Tue Mar 15 09:41:03 CET 2016 x86_64 GNU/Linux

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Zachary Vance

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