Re: Setting large MTU size on slave interfaces may stall the whole system

[Or Gerlitz]

On Tue, Dec 12, 2017 at 5:21 AM, Qing Huang <qing.huang@xxxxxxxxxx> wrote:
> Hi,
>
> We found an issue with the bonding driver when testing Mellanox devices.
> The following test commands will stall the whole system sometimes, with
> serial console
> flooded with log messages from the bond_miimon_inspect() function. Setting
> mtu size
> to be 1500 seems okay but very rarely it may hit the same problem too.
>
> ip address flush dev ens3f0
> ip link set dev ens3f0 down
> ip address flush dev ens3f1
> ip link set dev ens3f1 down
> [root@ca-hcl629 etc]# modprobe bonding mode=0 miimon=250 use_carrier=1
> updelay=500 downdelay=500
> [root@ca-hcl629 etc]# ifconfig bond0 up
> [root@ca-hcl629 etc]# ifenslave bond0 ens3f0 ens3f1
> [root@ca-hcl629 etc]# ip link set bond0 mtu 4500 up

> Seiral console output:
>
> ** 4 printk messages dropped ** [ 3717.743761] bond0: link status down for
> interface ens3f0, disabling it in 500 ms
[..]


> It seems that when setting a large mtu size on an RoCE interface, the RTNL
> mutex may be held too long by the slave
> interface, causing bond_mii_monitor() to be called repeatedly at an interval
> of 1 tick (1K HZ kernel configuration) and kernel to become unresponsive.

Did you try/managed to reproduce that also with other NIC drivers?

Or.