Re: INFO: rcu detected stall in dummy_timer

From: Alan Stern
Date: Fri Sep 13 2019 - 16:36:00 EST

On Fri, 13 Sep 2019, syzbot wrote:

> syzbot has found a reproducer for the following crash on:
> HEAD commit: f0df5c1b usb-fuzzer: main usb gadget fuzzer driver
> git tree: usb-fuzzer
> console output:
> kernel config:
> dashboard link:
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:
> C reproducer:
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+b24d736f18a1541ad550@xxxxxxxxxxxxxxxxxxxxxxxxx
> yurex 3-1:0.101: yurex_interrupt - unknown status received: -71
> yurex 5-1:0.101: yurex_interrupt - unknown status received: -71
> yurex 6-1:0.101: yurex_interrupt - unknown status received: -71
> rcu: INFO: rcu_sched self-detected stall on CPU


This problem may be a result of overloading dummy_timer. The kernel
config you are using has CONFIG_HZ=100, but dummy-hcd needs
CONFIG_HZ=1000 (see the comment on line 1789). That is, lower values
of HZ will occasionally lead to trouble, and this may be an example.

Can you change the config value for HZ and see if the bug still

Alan Stern