On Fri, Jul 31, 2020 at 6:08 PM Randy Dunlap <[email protected]> wrote: > > 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.
Hi Randy, Thanks for looking into this. But I think I messed things up. The config has CONFIG_RCU_CPU_STALL_TIMEOUT=100, but this is not an RCU stall: watchdog: BUG: soft lockup - CPU#3 stuck for 21s! [grep:4749] This is what is controlled by kernel.watchdog_thresh sysctl (?).
