Hello,

I have a BTRFS filesystem that is reverting to read-only after a few 
moments of use. There is a stack trace visible in the kernel log, which 
is attached.

Here is my system information:

# uname -a

Linux rescue 4.7.2-1-ARCH #1 SMP PREEMPT Sat Aug 20 23:02:56 CEST 2016 
x86_64 GNU/Linux

# btrfs --version

btrfs-progs v4.7

# btrfs fi show

Label: 'linux'  uuid: 79862c20-d0b0-4ffa-a9af-e3a40868a243
         Total devices 1 FS bytes used 284.60GiB
         devid    1 size 300.03GiB used 300.03GiB path /dev/sdb5

# btrfs fi df /mnt

Data, single: total=278.00GiB, used=274.68GiB
System, DUP: total=8.00MiB, used=64.00KiB
System, single: total=4.00MiB, used=0.00B
Metadata, DUP: total=11.00GiB, used=9.92GiB
Metadata, single: total=8.00MiB, used=0.00B
GlobalReserve, single: total=512.00MiB, used=0.00B

As soon as the problem started, I saw that the Metadata, DUP was 
completely used. It become a little better (like above) after a scrub.
I can easily recover disk space by removing old snapshots, if needed.

The dmesg output is attached.

Before making further recovery attempts, or even restoring from backup, 
I would like to ask for the best option to proceed.

Thanks,

Cesar