I'm running the following configuration:

# brctl show

bridge name     bridge id               STP enabled     interfaces
br0             8000.000000000000       no
br1             8000.000ae72c442a       no              enp5s0
                                                        vnet0
                                                        vnet2
br2             8000.fe5400884ea1       no              vnet1
                                                        vnet4
                                                        vnet7
br3             8000.fe5400b6254b       no              vnet3
                                                        vnet5
                                                        vnet8
br4             8000.fe540056bde0       no              vnet6
                                                        vnet9
# uname -a
Linux linux-8dae 3.16.7-21-desktop #1 SMP PREEMPT Tue Apr 14 07:11:37 UTC 2015
(93c1539) x86_64 x86_64 x86_64 GNU/Linux

# modinfo bridge

filename:       /lib/modules/3.16.7-21-desktop/kernel/net/bridge/bridge.ko
alias:          rtnl-link-bridge
version:        2.3
license:        GPL
srcversion:     9745B10185954B34BA9A365
depends:        stp,llc
intree:         Y
vermagic:       3.16.7-21-desktop SMP preempt mod_unload modversions 
signer:         openSUSE Secure Boot Signkey
sig_key:        03:32:FA:9C:BF:0D:88:BF:21:92:4B:0D:E8:2A:09:A5:4D:5D:EF:C8
sig_hashalgo:   sha256


# modinfo r8168
filename:      
/lib/modules/3.16.7-21-desktop/kernel/drivers/net/ethernet/realtek/r8168.ko
version:        8.039.00-NAPI
license:        GPL
description:    RealTek RTL-8168 Gigabit Ethernet driver
author:         Realtek and the Linux r8168 crew <netdev@vger.kernel.org>
srcversion:     1ABAB2C5CDB55DDB867B0D8
alias:          pci:v00001186d00004300sv00001186sd00004B10bc*sc*i*
alias:          pci:v000010ECd00008168sv*sd*bc*sc*i*
depends:        
vermagic:       3.16.7-7-desktop SMP preempt mod_unload modversions 
parm:           speed:force phy operation. Deprecated by ethtool (8). (ushort)
parm:           duplex:force phy operation. Deprecated by ethtool (8). (int)
parm:           autoneg:force phy operation. Deprecated by ethtool (8). (int)
parm:           aspm:Enable ASPM. (int)
parm:           s5wol:Enable Shutdown Wake On Lan. (int)
parm:           rx_copybreak:Copy breakpoint for copy-only-tiny-frames (int)
parm:           timer_count:Timer Interrupt Interval. (int)
parm:           eee_enable:Enable Energy Efficient Ethernet. (int)
parm:           debug:Debug verbosity level (0=none, ..., 16=all) (int)

# modinfo vhost_net
filename:      
/lib/modules/3.16.7-21-desktop/kernel/drivers/vhost/vhost_net.ko
alias:          devname:vhost-net
alias:          char-major-10-238
description:    Host kernel accelerator for virtio net
author:         Michael S. Tsirkin
license:        GPL v2
version:        0.0.1
srcversion:     FB9CD9FD03A82F6981775C2
depends:        vhost,tun,macvtap
intree:         Y
vermagic:       3.16.7-21-desktop SMP preempt mod_unload modversions 
signer:         openSUSE Secure Boot Signkey
sig_key:        03:32:FA:9C:BF:0D:88:BF:21:92:4B:0D:E8:2A:09:A5:4D:5D:EF:C8
sig_hashalgo:   sha256
parm:           experimental_zcopytx:Enable Zero Copy TX; 1 -Enable; 0 -
Disable (int)

Randomly the br1 bridge stops to bridge traffic and it is impossible to recover
without restarting the system, even if I delete and reconfigure the bridge. 

The enp5s0 and the vnet (KVM hosts) interfaces are working without any apparent
problem, i.e. tcpdump shows unbridged traffic.

Unfortunately I could not find any error message (dmesg, journalctl, etc) that
can be of any help. I did also try to log the traffic with ebtables but nothing
interesting/relevant is displayed.

Now the question is how I can produce meaningful debugging information, i.e. a
dump of the internal tables is have read are used by the bridge module,
unfortunately I did not find any useful information on how I can provide this
information.

Tnx and have a nice day

Marco