Btrfs devel - Aug 2013 - Unable to unmount filesystem (bug in kernel reported in kern.log)

I tried to unmount a btrfs filesystem located in a external usb hard
drive. This belonged to a raid1 data and metadata filesystem mounted
in degraded mode.

Unfortunately, I couldn''t save the image of filesystem but I could see
this error in kern.log:

Aug  4 02:23:55 rohan kernel: [ 3747.840027] usb 1-3: new high-speed
USB device number 8 using ehci_hcd
Aug  4 02:23:55 rohan kernel: [ 3747.973554] usb-storage 1-3:1.0:
Quirks match for vid 14cd pid 6600: 20
Aug  4 02:23:55 rohan kernel: [ 3747.973584] scsi8 : usb-storage 1-3:1.0
Aug  4 02:23:56 rohan kernel: [ 3748.972895] scsi 8:0:0:0:
Direct-Access     ST316002 1A                    PQ: 0 ANSI: 0
Aug  4 02:23:56 rohan kernel: [ 3748.973642] sd 8:0:0:0: Attached scsi
generic sg9 type 0
Aug  4 02:23:56 rohan kernel: [ 3748.974408] sd 8:0:0:0: [sdi]
312581808 512-byte logical blocks: (160 GB/149 GiB)
Aug  4 02:23:56 rohan kernel: [ 3748.975660] sd 8:0:0:0: [sdi] Write
Protect is off
Aug  4 02:23:56 rohan kernel: [ 3748.975664] sd 8:0:0:0: [sdi] Mode
Sense: 03 00 00 00
Aug  4 02:23:56 rohan kernel: [ 3748.976262] sd 8:0:0:0: [sdi] No
Caching mode page present
Aug  4 02:23:56 rohan kernel: [ 3748.976266] sd 8:0:0:0: [sdi]
Assuming drive cache: write through
Aug  4 02:23:56 rohan kernel: [ 3748.978006] sd 8:0:0:0: [sdi] No
Caching mode page present
Aug  4 02:23:56 rohan kernel: [ 3748.978009] sd 8:0:0:0: [sdi]
Assuming drive cache: write through
Aug  4 02:23:56 rohan kernel: [ 3748.998148]  sdi: sdi1
Aug  4 02:23:56 rohan kernel: [ 3749.000138] sd 8:0:0:0: [sdi] No
Caching mode page present
Aug  4 02:23:56 rohan kernel: [ 3749.000142] sd 8:0:0:0: [sdi]
Assuming drive cache: write through
Aug  4 02:23:56 rohan kernel: [ 3749.000146] sd 8:0:0:0: [sdi]
Attached SCSI disk
Aug  4 02:24:26 rohan kernel: [ 3778.904274] device fsid
ab74ba21-3b11-42f1-b388-f3a7c059e7eb devid 1 transid 9 /dev/sdi1
Aug  4 02:24:26 rohan kernel: [ 3778.924259] btrfs: disk space caching
is enabled
Aug  4 02:25:36 rohan kernel: [ 3849.110130] btrfs: space cache
generation (8) does not match inode (12)
Aug  4 02:25:36 rohan kernel: [ 3849.110138] btrfs: failed to load
free space cache for block group 29360128
Aug  4 02:26:06 rohan kernel: [ 3878.947113] parent transid verify
failed on 30580736 wanted 12 found 8
Aug  4 02:26:06 rohan kernel: [ 3878.947120] parent transid verify
failed on 30580736 wanted 12 found 8
Aug  4 02:26:06 rohan kernel: [ 3878.947124] parent transid verify
failed on 30580736 wanted 12 found 8
Aug  4 02:26:06 rohan kernel: [ 3878.947129] parent transid verify
failed on 30580736 wanted 12 found 8
Aug  4 02:26:06 rohan kernel: [ 3878.947132] parent transid verify
failed on 30580736 wanted 12 found 8
Aug  4 02:26:06 rohan kernel: [ 3878.947156] ------------[ cut here
]------------
Aug  4 02:26:06 rohan kernel: [ 3878.947184] kernel BUG at
/build/buildd/linux-3.2.0/fs/btrfs/inode.c:806!
Aug  4 02:26:06 rohan kernel: [ 3878.947216] invalid opcode: 0000 [#1] SMP
Aug  4 02:26:06 rohan kernel: [ 3878.947238] CPU 1
Aug  4 02:26:06 rohan kernel: [ 3878.947248] Modules linked in: btrfs
zlib_deflate libcrc32c pci_stub vboxpci(O) vboxnetadp(O) vboxnetflt(O)
vboxdrv(O) xt_recent xt_state xt_tcpudp iptable_nat nf_nat
nf_conntrack_ipv4 nf_conntrack nf_defrag_ipv4 iptable_filter ip_tables
x_tables rfcomm bnep bluetooth parport_pc ppdev binfmt_misc dm_crypt
snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep snd_pcm
snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq snd_timer
snd_seq_device snd asus_atk0110 psmouse soundcore snd_page_alloc
serio_raw lp parport mac_hid usbhid hid usb_storage i915 r8169
drm_kms_helper drm i2c_algo_bit video
Aug  4 02:26:06 rohan kernel: [ 3878.947556]
Aug  4 02:26:06 rohan kernel: [ 3878.947566] Pid: 4629, comm:
btrfs-transacti Tainted: G           O 3.2.0-51-generic #77-Ubuntu
System manufacturer System Product Name/P5KPL-AM SE
Aug  4 02:26:06 rohan kernel: [ 3878.947628] RIP:
0010:[<ffffffffa050c538>]  [<ffffffffa050c538>]
cow_file_range+0x388/0x3a0 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.947687] RSP:
0018:ffff880061bfd6a0  EFLAGS: 00010246
Aug  4 02:26:06 rohan kernel: [ 3878.947712] RAX: ffff8800d8ede000
RBX: 0000000000000000 RCX: 000000000000ffff
Aug  4 02:26:06 rohan kernel: [ 3878.947743] RDX: ffff8800d6fcf000
RSI: ffffea00044892c0 RDI: ffff88007aa08910
Aug  4 02:26:06 rohan kernel: [ 3878.947775] RBP: ffff880061bfd760
R08: ffff880061bfd94c R09: ffff880061bfd940
Aug  4 02:26:06 rohan kernel: [ 3878.947807] R10: 0000000000000002
R11: 0000000000000001 R12: ffff88007aa08910
Aug  4 02:26:06 rohan kernel: [ 3878.947839] R13: 0000000000001000
R14: 000000000000ffff R15: ffff88007aa08780
Aug  4 02:26:06 rohan kernel: [ 3878.947871] FS:
0000000000000000(0000) GS:ffff88011fc80000(0000)
knlGS:0000000000000000
Aug  4 02:26:06 rohan kernel: [ 3878.947907] CS:  0010 DS: 0000 ES:
0000 CR0: 000000008005003b
Aug  4 02:26:06 rohan kernel: [ 3878.947933] CR2: 00007ff051357019
CR3: 00000000d9913000 CR4: 00000000000406e0
Aug  4 02:26:06 rohan kernel: [ 3878.947965] DR0: 0000000000000000
DR1: 0000000000000000 DR2: 0000000000000000
Aug  4 02:26:06 rohan kernel: [ 3878.949197] DR3: 0000000000000000
DR6: 00000000ffff0ff0 DR7: 0000000000000400
Aug  4 02:26:06 rohan kernel: [ 3878.950413] Process btrfs-transacti
(pid: 4629, threadinfo ffff880061bfc000, task ffff8800d10fae00)
Aug  4 02:26:06 rohan kernel: [ 3878.951105] Stack:
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  ffff880061bfd6b0
ffff880075553948 0000000000000286 ffff880061bfd6d0
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  0000000000000286
ffff880075553948 ffff880061bfd710 ffffea00044892c0
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  0080ffffffffffff
ffff8800d6fcf000 ffff88006a53f2d0 ffff880061bfd94c
Aug  4 02:26:06 rohan kernel: [ 3878.951105] Call Trace:
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0533120>] ?
btrfs_tree_read_unlock_blocking+0x40/0x60 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa050c8e7>]
run_delalloc_nocow+0x397/0x7a0 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa050cd47>]
run_delalloc_range+0x57/0x80 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa052303d>]
__extent_writepage+0x5bd/0x700 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8131443d>] ?
radix_tree_gang_lookup_tag_slot+0x8d/0xd0
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0523442>]
extent_write_cache_pages.isra.21.constprop.31+0x2c2/0x3e0 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa05237a5>]
extent_writepages+0x45/0x60 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa05085d0>] ?
btrfs_read_locked_inode+0x390/0x390 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa051fade>] ?
clear_extent_bit+0x1ce/0x3f0 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0506ff8>]
btrfs_writepages+0x28/0x30 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff811245c1>]
do_writepages+0x21/0x40
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8111a8bb>]
__filemap_fdatawrite_range+0x5b/0x60
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8111b2af>]
filemap_fdatawrite+0x1f/0x30
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8111b2f5>]
filemap_write_and_wait+0x35/0x60
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa053ad2f>]
__btrfs_write_out_cache+0x6cf/0x950 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff816606be>] ?
_raw_spin_lock+0xe/0x20
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa053b069>]
btrfs_write_out_cache+0xb9/0xf0 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa04f4424>]
btrfs_write_dirty_block_groups+0x224/0x280 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0502b62>]
update_cowonly_root+0x42/0xd0 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0502cac>]
commit_cowonly_roots+0xbc/0x100 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa050448f>]
btrfs_commit_transaction+0x3bf/0x840 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8108c230>] ?
add_wait_queue+0x60/0x60
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa04fd3b5>]
transaction_kthread+0x265/0x280 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa04fd150>] ?
btrfs_congested_fn+0xb0/0xb0 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8108b78c>]
kthread+0x8c/0xa0
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8166ae74>]
kernel_thread_helper+0x4/0x10
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8108b700>] ?
flush_kthread_worker+0xa0/0xa0
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8166ae70>] ?
gs_change+0x13/0x13
Aug  4 02:26:06 rohan kernel: [ 3878.951105] Code: 10 c7 02 01 00 00
00 e9 4a ff ff ff 48 8b 7d 80 4c 89 e6 4c 89 95 68 ff ff ff e8 d4 6f
00 00 4c 8b 95 68 ff ff ff e9 4c fd ff ff <0f> 0b 0f 0b 0f 0b 0f 0b 0f
0b 0f 0b 66 66 66 2e 0f 1f 84 00 00
Aug  4 02:26:06 rohan kernel: [ 3878.951105] RIP  [<ffffffffa050c538>]
cow_file_range+0x388/0x3a0 [btrfs]
Aug  4 02:26:06 rohan kernel: [ 3878.951105]  RSP <ffff880061bfd6a0>
Aug  4 02:26:06 rohan kernel: [ 3879.008489] ---[ end trace
6751139acfeba416 ]---
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On 8/4/13 6:58 PM, Alfredo Esteban wrote:
> I tried to unmount a btrfs filesystem located in a external usb hard
> drive. This belonged to a raid1 data and metadata filesystem mounted
> in degraded mode.
> 
> Unfortunately, I couldn''t save the image of filesystem but I could
see
> this error in kern.log:
> 
> Aug  4 02:23:55 rohan kernel: [ 3747.840027] usb 1-3: new high-speed
> USB device number 8 using ehci_hcd
> Aug  4 02:23:55 rohan kernel: [ 3747.973554] usb-storage 1-3:1.0:
> Quirks match for vid 14cd pid 6600: 20
> Aug  4 02:23:55 rohan kernel: [ 3747.973584] scsi8 : usb-storage 1-3:1.0
> Aug  4 02:23:56 rohan kernel: [ 3748.972895] scsi 8:0:0:0:
> Direct-Access     ST316002 1A                    PQ: 0 ANSI: 0
> Aug  4 02:23:56 rohan kernel: [ 3748.973642] sd 8:0:0:0: Attached scsi
> generic sg9 type 0
> Aug  4 02:23:56 rohan kernel: [ 3748.974408] sd 8:0:0:0: [sdi]
> 312581808 512-byte logical blocks: (160 GB/149 GiB)
> Aug  4 02:23:56 rohan kernel: [ 3748.975660] sd 8:0:0:0: [sdi] Write
> Protect is off
> Aug  4 02:23:56 rohan kernel: [ 3748.975664] sd 8:0:0:0: [sdi] Mode
> Sense: 03 00 00 00
> Aug  4 02:23:56 rohan kernel: [ 3748.976262] sd 8:0:0:0: [sdi] No
> Caching mode page present
> Aug  4 02:23:56 rohan kernel: [ 3748.976266] sd 8:0:0:0: [sdi]
> Assuming drive cache: write through
> Aug  4 02:23:56 rohan kernel: [ 3748.978006] sd 8:0:0:0: [sdi] No
> Caching mode page present
> Aug  4 02:23:56 rohan kernel: [ 3748.978009] sd 8:0:0:0: [sdi]
> Assuming drive cache: write through
> Aug  4 02:23:56 rohan kernel: [ 3748.998148]  sdi: sdi1
> Aug  4 02:23:56 rohan kernel: [ 3749.000138] sd 8:0:0:0: [sdi] No
> Caching mode page present
> Aug  4 02:23:56 rohan kernel: [ 3749.000142] sd 8:0:0:0: [sdi]
> Assuming drive cache: write through
> Aug  4 02:23:56 rohan kernel: [ 3749.000146] sd 8:0:0:0: [sdi]
> Attached SCSI disk
> Aug  4 02:24:26 rohan kernel: [ 3778.904274] device fsid
> ab74ba21-3b11-42f1-b388-f3a7c059e7eb devid 1 transid 9 /dev/sdi1
> Aug  4 02:24:26 rohan kernel: [ 3778.924259] btrfs: disk space caching
> is enabled
> Aug  4 02:25:36 rohan kernel: [ 3849.110130] btrfs: space cache
> generation (8) does not match inode (12)
> Aug  4 02:25:36 rohan kernel: [ 3849.110138] btrfs: failed to load
> free space cache for block group 29360128
> Aug  4 02:26:06 rohan kernel: [ 3878.947113] parent transid verify
> failed on 30580736 wanted 12 found 8
> Aug  4 02:26:06 rohan kernel: [ 3878.947120] parent transid verify
> failed on 30580736 wanted 12 found 8
> Aug  4 02:26:06 rohan kernel: [ 3878.947124] parent transid verify
> failed on 30580736 wanted 12 found 8
> Aug  4 02:26:06 rohan kernel: [ 3878.947129] parent transid verify
> failed on 30580736 wanted 12 found 8
> Aug  4 02:26:06 rohan kernel: [ 3878.947132] parent transid verify
> failed on 30580736 wanted 12 found 8
> Aug  4 02:26:06 rohan kernel: [ 3878.947156] ------------[ cut here
> ]------------
> Aug  4 02:26:06 rohan kernel: [ 3878.947184] kernel BUG at
> /build/buildd/linux-3.2.0/fs/btrfs/inode.c:806!
This is against the 3.2 kernel, which is now 19 months old and ancient
in terms of btrfs support. Please see if you can reproduce with a more
recent kernel. Otherwise, file a bug report with Ubuntu if they are
doing substantial btrfs backports.

-Jeff
> Aug  4 02:26:06 rohan kernel: [ 3878.947216] invalid opcode: 0000 [#1] SMP
> Aug  4 02:26:06 rohan kernel: [ 3878.947238] CPU 1
> Aug  4 02:26:06 rohan kernel: [ 3878.947248] Modules linked in: btrfs
> zlib_deflate libcrc32c pci_stub vboxpci(O) vboxnetadp(O) vboxnetflt(O)
> vboxdrv(O) xt_recent xt_state xt_tcpudp iptable_nat nf_nat
> nf_conntrack_ipv4 nf_conntrack nf_defrag_ipv4 iptable_filter ip_tables
> x_tables rfcomm bnep bluetooth parport_pc ppdev binfmt_misc dm_crypt
> snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep snd_pcm
> snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq snd_timer
> snd_seq_device snd asus_atk0110 psmouse soundcore snd_page_alloc
> serio_raw lp parport mac_hid usbhid hid usb_storage i915 r8169
> drm_kms_helper drm i2c_algo_bit video
> Aug  4 02:26:06 rohan kernel: [ 3878.947556]
> Aug  4 02:26:06 rohan kernel: [ 3878.947566] Pid: 4629, comm:
> btrfs-transacti Tainted: G           O 3.2.0-51-generic #77-Ubuntu
> System manufacturer System Product Name/P5KPL-AM SE
> Aug  4 02:26:06 rohan kernel: [ 3878.947628] RIP:
> 0010:[<ffffffffa050c538>]  [<ffffffffa050c538>]
> cow_file_range+0x388/0x3a0 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.947687] RSP:
> 0018:ffff880061bfd6a0  EFLAGS: 00010246
> Aug  4 02:26:06 rohan kernel: [ 3878.947712] RAX: ffff8800d8ede000
> RBX: 0000000000000000 RCX: 000000000000ffff
> Aug  4 02:26:06 rohan kernel: [ 3878.947743] RDX: ffff8800d6fcf000
> RSI: ffffea00044892c0 RDI: ffff88007aa08910
> Aug  4 02:26:06 rohan kernel: [ 3878.947775] RBP: ffff880061bfd760
> R08: ffff880061bfd94c R09: ffff880061bfd940
> Aug  4 02:26:06 rohan kernel: [ 3878.947807] R10: 0000000000000002
> R11: 0000000000000001 R12: ffff88007aa08910
> Aug  4 02:26:06 rohan kernel: [ 3878.947839] R13: 0000000000001000
> R14: 000000000000ffff R15: ffff88007aa08780
> Aug  4 02:26:06 rohan kernel: [ 3878.947871] FS:
> 0000000000000000(0000) GS:ffff88011fc80000(0000)
> knlGS:0000000000000000
> Aug  4 02:26:06 rohan kernel: [ 3878.947907] CS:  0010 DS: 0000 ES:
> 0000 CR0: 000000008005003b
> Aug  4 02:26:06 rohan kernel: [ 3878.947933] CR2: 00007ff051357019
> CR3: 00000000d9913000 CR4: 00000000000406e0
> Aug  4 02:26:06 rohan kernel: [ 3878.947965] DR0: 0000000000000000
> DR1: 0000000000000000 DR2: 0000000000000000
> Aug  4 02:26:06 rohan kernel: [ 3878.949197] DR3: 0000000000000000
> DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Aug  4 02:26:06 rohan kernel: [ 3878.950413] Process btrfs-transacti
> (pid: 4629, threadinfo ffff880061bfc000, task ffff8800d10fae00)
> Aug  4 02:26:06 rohan kernel: [ 3878.951105] Stack:
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  ffff880061bfd6b0
> ffff880075553948 0000000000000286 ffff880061bfd6d0
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  0000000000000286
> ffff880075553948 ffff880061bfd710 ffffea00044892c0
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  0080ffffffffffff
> ffff8800d6fcf000 ffff88006a53f2d0 ffff880061bfd94c
> Aug  4 02:26:06 rohan kernel: [ 3878.951105] Call Trace:
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0533120>] ?
> btrfs_tree_read_unlock_blocking+0x40/0x60 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa050c8e7>]
> run_delalloc_nocow+0x397/0x7a0 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa050cd47>]
> run_delalloc_range+0x57/0x80 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa052303d>]
> __extent_writepage+0x5bd/0x700 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8131443d>] ?
> radix_tree_gang_lookup_tag_slot+0x8d/0xd0
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0523442>]
> extent_write_cache_pages.isra.21.constprop.31+0x2c2/0x3e0 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa05237a5>]
> extent_writepages+0x45/0x60 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa05085d0>] ?
> btrfs_read_locked_inode+0x390/0x390 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa051fade>] ?
> clear_extent_bit+0x1ce/0x3f0 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0506ff8>]
> btrfs_writepages+0x28/0x30 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff811245c1>]
> do_writepages+0x21/0x40
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8111a8bb>]
> __filemap_fdatawrite_range+0x5b/0x60
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8111b2af>]
> filemap_fdatawrite+0x1f/0x30
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8111b2f5>]
> filemap_write_and_wait+0x35/0x60
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa053ad2f>]
> __btrfs_write_out_cache+0x6cf/0x950 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff816606be>] ?
> _raw_spin_lock+0xe/0x20
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa053b069>]
> btrfs_write_out_cache+0xb9/0xf0 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa04f4424>]
> btrfs_write_dirty_block_groups+0x224/0x280 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0502b62>]
> update_cowonly_root+0x42/0xd0 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa0502cac>]
> commit_cowonly_roots+0xbc/0x100 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa050448f>]
> btrfs_commit_transaction+0x3bf/0x840 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8108c230>] ?
> add_wait_queue+0x60/0x60
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa04fd3b5>]
> transaction_kthread+0x265/0x280 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffffa04fd150>] ?
> btrfs_congested_fn+0xb0/0xb0 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8108b78c>]
> kthread+0x8c/0xa0
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8166ae74>]
> kernel_thread_helper+0x4/0x10
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8108b700>] ?
> flush_kthread_worker+0xa0/0xa0
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  [<ffffffff8166ae70>] ?
> gs_change+0x13/0x13
> Aug  4 02:26:06 rohan kernel: [ 3878.951105] Code: 10 c7 02 01 00 00
> 00 e9 4a ff ff ff 48 8b 7d 80 4c 89 e6 4c 89 95 68 ff ff ff e8 d4 6f
> 00 00 4c 8b 95 68 ff ff ff e9 4c fd ff ff <0f> 0b 0f 0b 0f 0b 0f 0b
0f
> 0b 0f 0b 66 66 66 2e 0f 1f 84 00 00
> Aug  4 02:26:06 rohan kernel: [ 3878.951105] RIP 
[<ffffffffa050c538>]
> cow_file_range+0x388/0x3a0 [btrfs]
> Aug  4 02:26:06 rohan kernel: [ 3878.951105]  RSP <ffff880061bfd6a0>
> Aug  4 02:26:06 rohan kernel: [ 3879.008489] ---[ end trace
> 6751139acfeba416 ]---
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-- 
Jeff Mahoney
SUSE Labs

Jeff Mahoney posted on Sun, 04 Aug 2013 22:27:31 -0400 as excerpted:
> On 8/4/13 6:58 PM, Alfredo Esteban wrote:
>> I tried to unmount a btrfs filesystem located in a external usb hard
>> drive. This belonged to a raid1 data and metadata filesystem mounted in
>> degraded mode.
>> 
>> Unfortunately, I couldn''t save the image of filesystem but I
could see
>> this error in kern.log:
[snip]
>> Aug  4 02:26:06 rohan kernel: [ 3878.947184] kernel BUG at
>> /build/buildd/linux-3.2.0/fs/btrfs/inode.c:806!
> 
> This is against the 3.2 kernel, which is now 19 months old and ancient
> in terms of btrfs support. Please see if you can reproduce with a more
> recent kernel. Otherwise, file a bug report with Ubuntu if they are
> doing substantial btrfs backports.
Seconded.

Also, if you''re not aware of the btrfs wiki yet, you probably want to 
read up on btrfs there.  It stresses btrfs'' development nature and the 
importance of running a current kernel for btrfs testing in several 
places, so the fact that you''re not doing so indicates that you
probably
hadn''t read the wiki, and are thus likely missing out on other 
potentially very useful information, as well.

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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