Re: Selftest failures related to kern_sync_rcu()

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:

> On Wed, Apr 14, 2021 at 10:52 AM Paul E. McKenney <paulmck@kernel.org> wrote:
>>
>> > > > >                 if (num_online_cpus() > 1)
>> > > > >                         synchronize_rcu();
>>
>> In CONFIG_PREEMPT_NONE=y and CONFIG_PREEMPT_VOLUNTARY=y kernels, this
>> synchronize_rcu() will be a no-op anyway due to there only being the
>> one CPU.  Or are these failures all happening in CONFIG_PREEMPT=y kernels,
>> and in tests where preemption could result in the observed failures?
>>
>> Could you please send your .config file, or at least the relevant portions
>> of it?
>
> That's my understanding as well. I assumed Toke has preempt=y.
> Otherwise the whole thing needs to be root caused properly.

Running with a single CPU fails, with multiple CPUs succeeds.
Happens without PREEMPT as well:

$ egrep 'HZ|PREEMPT|RCU' .config
CONFIG_NO_HZ_COMMON=y
# CONFIG_HZ_PERIODIC is not set
CONFIG_NO_HZ_IDLE=y
# CONFIG_NO_HZ_FULL is not set
CONFIG_NO_HZ=y
# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set
# RCU Subsystem
CONFIG_TREE_RCU=y
CONFIG_RCU_EXPERT=y
CONFIG_SRCU=y
CONFIG_TREE_SRCU=y
CONFIG_TASKS_RCU_GENERIC=y
CONFIG_TASKS_RUDE_RCU=y
CONFIG_TASKS_TRACE_RCU=y
CONFIG_RCU_STALL_COMMON=y
CONFIG_RCU_NEED_SEGCBLIST=y
CONFIG_RCU_FANOUT=64
CONFIG_RCU_FANOUT_LEAF=16
# CONFIG_RCU_FAST_NO_HZ is not set
# CONFIG_RCU_NOCB_CPU is not set
# CONFIG_TASKS_TRACE_RCU_READ_MB is not set
# end of RCU Subsystem
# CONFIG_HZ_100 is not set
CONFIG_HZ_250=y
# CONFIG_HZ_300 is not set
# CONFIG_HZ_1000 is not set
CONFIG_HZ=250
CONFIG_MMU_GATHER_RCU_TABLE_FREE=y
CONFIG_HAVE_PREEMPT_DYNAMIC=y
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_MACHZ_WDT is not set
# RCU Debugging
# CONFIG_RCU_SCALE_TEST is not set
# CONFIG_RCU_TORTURE_TEST is not set
# CONFIG_RCU_REF_SCALE_TEST is not set
CONFIG_RCU_CPU_STALL_TIMEOUT=60
# CONFIG_RCU_TRACE is not set
# CONFIG_RCU_EQS_DEBUG is not set
# CONFIG_RCU_STRICT_GRACE_PERIOD is not set
# end of RCU Debugging
# CONFIG_PREEMPTIRQ_DELAY_TEST is not set

Anything else you need from .config?

-Toke