Re: WARN_ON_ONCE() in process_one_work()?

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Tue, Jul 03, 2018 at 01:12:05PM -0700, Tejun Heo wrote:
> Hello, Paul.
> 
> On Tue, Jul 03, 2018 at 09:40:44AM -0700, Paul E. McKenney wrote:
> > > I will apply this, but be advised that I have not seen that WARN_ON_ONCE()
> > > trigger since.  :-/
> > 
> > But I get a build error:
> > 
> > kernel/workqueue.o: In function `worker_attach_to_pool':
> > workqueue.c:(.text+0x63c): undefined reference to `cpuhp_target_state'
> > workqueue.c:(.text+0x647): undefined reference to `cpuhp_current_state'
> > /home/paulmck/public_git/linux-rcu/Makefile:1015: recipe for target 'vmlinux' failed
> > 
> > My guess is that the worker_attach_to_pool() code needs to change so
> > as to invoke cpuhp_current_state() and cpuhp_target_state() only in
> > CONFIG_HOTPLUG_CPU=y kernels, but I figured I should defer to you.
> 
> Just to clarify, the bug happened on a kernel with cpuhp enabled,
> right?

It seems to be a bit more complicated than that, despite my initial
confidence that I knew what was going on.  The build failed for these
rcutorture scenarios:

SRCU-N: (No idea!)

	CONFIG_RCU_TRACE=n
	CONFIG_SMP=y
	CONFIG_NR_CPUS=4
	CONFIG_HOTPLUG_CPU=y
	CONFIG_PREEMPT_NONE=y
	CONFIG_PREEMPT_VOLUNTARY=n
	CONFIG_PREEMPT=n

SRCU-t:  (Expected, CONFIG_SMP=n)
SRCU-u:  (Expected, CONFIG_SMP=n)
TASKS02:  (Expected, CONFIG_SMP=n)
TASKS03:  (Expected, CONFIG_HOTPLUG_CPU=n)
TINY01:  (Expected, CONFIG_SMP=n)
TINY02:  (Expected, CONFIG_SMP=n)
TREE01:  (No idea!)

	CONFIG_SMP=y
	CONFIG_PREEMPT_NONE=n
	CONFIG_PREEMPT_VOLUNTARY=n
	CONFIG_PREEMPT=y
	CONFIG_HZ_PERIODIC=n
	CONFIG_NO_HZ_IDLE=y
	CONFIG_NO_HZ_FULL=n
	CONFIG_RCU_FAST_NO_HZ=y
	CONFIG_RCU_TRACE=y
	CONFIG_HOTPLUG_CPU=y
	CONFIG_MAXSMP=y
	CONFIG_CPUMASK_OFFSTACK=y
	CONFIG_RCU_NOCB_CPU=y
	CONFIG_DEBUG_LOCK_ALLOC=n
	CONFIG_RCU_BOOST=n
	CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
	CONFIG_RCU_EXPERT=y

TREE02 didn't fail despite having CONFIG_HOTPLUG_CPU=n!
TREE03:  (Expected, CONFIG_HOTPLUG_CPU=n)
TREE04:  (Expected, CONFIG_HOTPLUG_CPU=n)

TREE07:  (No idea!)

	CONFIG_NR_CPUS=16
	CONFIG_PREEMPT_NONE=y
	CONFIG_PREEMPT_VOLUNTARY=n
	CONFIG_PREEMPT=n
	CONFIG_HZ_PERIODIC=n
	CONFIG_NO_HZ_IDLE=n
	CONFIG_NO_HZ_FULL=y
	CONFIG_RCU_FAST_NO_HZ=n
	CONFIG_RCU_TRACE=y
	CONFIG_HOTPLUG_CPU=y
	CONFIG_RCU_FANOUT=2
	CONFIG_RCU_FANOUT_LEAF=2
	CONFIG_DEBUG_LOCK_ALLOC=n
	CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
	CONFIG_RCU_EXPERT=y

TREE08:  (Expected, CONFIG_HOTPLUG_CPU=n)
TREE09:  (Expected, CONFIG_SMP=n)

Thoughts?

							Thanx, Paul