Hi all,
with 3.16-rc1  rsync stops writing to my btrfs filesystem and stays at a 
D+ state.
git bisect showed that the problematic commit is:

762380ad9322951cea4ce9d24864265f9c66a916 is the first bad commit
commit 762380ad9322951cea4ce9d24864265f9c66a916
Author: Jens Axboe <axboe@fb.com>
Date:   Thu Jun 5 13:38:39 2014 -0600

     block: add notion of a chunk size for request merging

     Some drivers have different limits on what size a request should
     optimally be, depending on the offset of the request. Similar to
     dividing a device into chunks. Add a setting that allows the driver
     to inform the block layer of such a chunk size. The block layer will
     then prevent merging across the chunks.

     This is needed to optimally support NVMe with a non-zero stripe size.

     Signed-off-by: Jens Axboe <axboe@fb.com>

sysrq w gives:

[ 3287.169569] SysRq : Show Blocked State
[ 3287.169655]   task                        PC stack   pid father
[ 3287.169675] rsync           D 0000000000000001     0   626    613 
0x00000000
[ 3287.169685]  ffff8802037c7d08 0000000000000082 ffff8800cf2e7010 
0000000000014500
[ 3287.169693]  ffff8802037c7fd8 0000000000014500 ffff8800cf2e7010 
ffff8802037c7c98
[ 3287.169700]  0000000000000292 0000000000000292 ffff8802037c7c50 
ffff8802037c7c50
[ 3287.169706] Call Trace:
[ 3287.169722]  [<ffffffff814f71d2>] ? do_page_fault+0x22/0x30
[ 3287.169733]  [<ffffffff8101cd89>] ? read_tsc+0x9/0x20
[ 3287.169743]  [<ffffffff811379d0>] ? sleep_on_page+0x20/0x20
[ 3287.169749]  [<ffffffff814eff29>] schedule+0x29/0x70
[ 3287.169756]  [<ffffffff814f0214>] io_schedule+0x94/0xf0
[ 3287.169763]  [<ffffffff811379de>] sleep_on_page_killable+0xe/0x50
[ 3287.169770]  [<ffffffff814f0748>] __wait_on_bit_lock+0x48/0xb0
[ 3287.169777]  [<ffffffff8128c753>] ? radix_tree_lookup_slot+0x13/0x30
[ 3287.169785]  [<ffffffff81137b7a>] __lock_page_killable+0x6a/0x70
[ 3287.169792]  [<ffffffff810acec0>] ? autoremove_wake_function+0x40/0x40
[ 3287.169799]  [<ffffffff811398c8>] generic_file_aio_read+0x458/0x6a0
[ 3287.169808]  [<ffffffff811ab63a>] do_sync_read+0x5a/0x90
[ 3287.169816]  [<ffffffff811abc47>] vfs_read+0x97/0x160
[ 3287.169823]  [<ffffffff811ac886>] SyS_read+0x46/0xc0
[ 3287.169831]  [<ffffffff814fb969>] system_call_fastpath+0x16/0x1b

$ btrfs filesystem show /storage/btrfs
Label: none  uuid: bde3c349-9e08-45bb-8517-b9a6dda81e88
         Total devices 6 FS bytes used 8.58TiB
         devid    1 size 3.64TiB used 3.02TiB path /dev/sdf
         devid    2 size 1.82TiB used 1.20TiB path /dev/sda
         devid    3 size 1.82TiB used 1.20TiB path /dev/sdb
         devid    4 size 1.82TiB used 1.20TiB path /dev/sdc
         devid    5 size 1.82TiB used 1.20TiB path /dev/sdd
         devid    6 size 1.82TiB used 1.20TiB path /dev/sdh

Btrfs v3.14.2-dirty

$ btrfs fi df /storage/btrfs
Data, single: total=8.89TiB, used=8.51TiB
System, RAID1: total=32.00MiB, used=992.00KiB
Metadata, RAID1: total=69.00GiB, used=67.83GiB
unknown, single: total=512.00MiB, used=0.00

full dmesg attached
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