On 7/30/20 11:50 PM, Dmitry Vyukov wrote:
> On Fri, Jul 31, 2020 at 8:44 AM syzbot
> <[email protected]> wrote:
>>
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit: 92ed3019 Linux 5.8-rc7
>> git tree: upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=10e84cdf100000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=b45e47f6d958ae82
>> dashboard link: https://syzkaller.appspot.com/bug?extid=8472ea265fe32cc3bf78
>> compiler: gcc (GCC) 10.1.0-syz 20200507
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: [email protected]
>
> This is a qemu-kvm instance killing the host kernel somehow, the host
> kernel itself running qemu's is full of rcu stalls. I think this is
> not a bug in the tested kernel.
> We change rcu stall timeout to 120 seconds from the default 21s, but
> this happens only after boot using sysctls. I did not find any way to
> change the rcu timeout via cmdline/config (would be useful).
(adding Paul)
Documentation/RCU/stallwarn.rst says there is a Kconfig:
CONFIG_RCU_CPU_STALL_TIMEOUT
This kernel configuration parameter defines the period of time
that RCU will wait from the beginning of a grace period until it
issues an RCU CPU stall warning. This time period is normally
21 seconds.
and Documentation/admin-guide/kernel-parameters.txt has 2 RCU stall timeouts,
one for CPU and one for tasks:
rcupdate.rcu_cpu_stall_timeout= [KNL]
Set timeout for RCU CPU stall warning messages.
rcupdate.rcu_task_stall_timeout= [KNL]
Set timeout in jiffies for RCU task stall warning
messages. Disable with a value less than or equal
to zero.
--
~Randy
