Hi,

Env:
Ubuntu Server x86-64, 2.6.32-24
/ on ext4
data on iSCSI target + btrfs + compression

History:
FS (data) frozen; can't read(list) files from subdir, can't write file.
Sync hung.
Ctrl-Alt-Del, nothing. (more times) :(
Power off
Restart, segfault

# mount -t btrfs -o compress /dev/vdb1 /usr/local/backups
Segmentation fault

log:
Aug 31 02:10:08 backup kernel: [ 3438.774811] Btrfs loaded
Aug 31 02:10:22 backup kernel: [ 3453.166781] device fsid 334fb3f1a88e13c4-1a284cc7dd521ca7 devid 1 transid 16676 /dev/vdb1
Aug 31 02:10:22 backup kernel: [ 3453.167153] btrfs: use compression
Aug 31 02:10:22 backup kernel: [ 3453.168313] parent transid verify failed on 20979712 wanted 16630 found 16466
Aug 31 02:10:22 backup kernel: [ 3453.168414] parent transid verify failed on 20979712 wanted 16630 found 16466
Aug 31 02:10:22 backup kernel: [ 3453.168517] parent transid verify failed on 20979712 wanted 16630 found 16466
Aug 31 02:10:31 backup kernel: [ 3453.327303] CPU 0
Aug 31 02:10:31 backup kernel: [ 3453.327303] Modules linked in: btrfs zlib_deflate crc32c libcrc32c fbcon tileblit font joydev bitblit softcursor psmouse serio_raw vga16fb lp vgastate i2c_piix4 parport floppy usbhid hid
Aug 31 02:10:31 backup kernel: [ 3453.327303] Pid: 5314, comm: mount Not tainted 2.6.32-24-server #41-Ubuntu Bochs
Aug 31 02:10:31 backup kernel: [ 3453.327303] RIP: 0010:[] [] __btrfs_map_block+0x3a1/0x530 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] RSP: 0018:ffff88001585f928 EFLAGS: 00010296
Aug 31 02:10:31 backup kernel: [ 3453.327303] RAX: 0000000000000043 RBX: 00000116f9a9a000 RCX: 0000000000000000
Aug 31 02:10:31 backup kernel: [ 3453.327303] RDX: 0000000000000000 RSI: 0000000000000086 RDI: 0000000000000246
Aug 31 02:10:31 backup kernel: [ 3453.327303] RBP: ffff88001585f9a8 R08: 00000000ffffffff R09: 0000000000000000
Aug 31 02:10:31 backup kernel: [ 3453.327303] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88001585f9f8
Aug 31 02:10:31 backup kernel: [ 3453.327303] R13: 0000000000000000 R14: 0000000000000001 R15: ffff880016a2c0f0
Aug 31 02:10:31 backup kernel: [ 3453.327303] FS: 00007fa28a5647e0(0000) GS:ffff880001c00000(0000) knlGS:0000000000000000
Aug 31 02:10:31 backup kernel: [ 3453.327303] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
Aug 31 02:10:31 backup kernel: [ 3453.327303] CR2: 00000000014bd180 CR3: 000000001597c000 CR4: 00000000000006f0
Aug 31 02:10:31 backup kernel: [ 3453.327303] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Aug 31 02:10:31 backup kernel: [ 3453.327303] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Aug 31 02:10:31 backup kernel: [ 3453.327303] Process mount (pid: 5314, threadinfo ffff88001585e000, task ffff880016b58000)
Aug 31 02:10:31 backup kernel: [ 3453.327303] 000000001585f978 0000100000000000 000000008b7cd4d0 00000000004f74b0
Aug 31 02:10:31 backup kernel: [ 3453.327303] <0> 0000000000001000 ffff88001585fa00 0000000000000000 ffff880016a2c0e8
Aug 31 02:10:31 backup kernel: [ 3453.327303] <0> ffff8800120307c0 0000000100000000 ffff88001585fa98 0000000000000000
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] btrfs_map_block+0x1a/0x20 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] btrfs_map_bio+0x5b/0x210 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] btree_submit_bio_hook+0xb0/0xc0 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] submit_one_bio+0x58/0x90 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] read_extent_buffer_pages+0x2ca/0x3e0 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] ? btree_get_extent+0x0/0x1b0 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] btree_read_extent_buffer_pages+0x5d/0xc0 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] read_tree_block+0x3c/0x60 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] find_and_setup_root+0xad/0xf0 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] ? _spin_lock+0xe/0x20
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] open_ctree+0xe10/0x1600 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] ? snprintf+0x34/0x40
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] btrfs_fill_super+0x6f/0x120 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] ? disk_name+0x64/0xc0
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] ? strlcpy+0x4a/0x60
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] btrfs_get_sb+0x2a7/0x310 [btrfs]
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] ? alloc_pages_current+0x87/0xd0
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] vfs_kern_mount+0x7b/0x1b0
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] do_kern_mount+0x52/0x130
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] do_mount+0x200/0x250
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] ? copy_mount_options+0xf2/0x1a0
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] sys_mount+0x90/0xe0
Aug 31 02:10:31 backup kernel: [ 3453.327303] [] system_call_fastpath+0x16/0x1b
Aug 31 02:10:31 backup kernel: [ 3453.327303] RSP
Aug 31 02:10:31 backup kernel: [ 3462.069163] ---[ end trace 8ffba131bfeb7d1a ]---

Made latest btrfs-tool (Btrfs v0.19-16-g075587c),
# ./btrfsck /dev/vdb1
parent transid verify failed on 20979712 wanted 16630 found 16466
parent transid verify failed on 20979712 wanted 16630 found 16466
parent transid verify failed on 20979712 wanted 16630 found 16466
btrfsck: disk-io.c:721: open_ctree_fd: Assertion `!(!chunk_root->node)' failed.
Aborted

So. Is there any chance to get back any data?

Peter