Hello!

I am hitting this WARN_ON_ONCE() in process_one_work() and am wondering
what I did wrong to make this happen:

------------------------------------------------------------------------

static void process_one_work(struct worker *worker, struct work_struct *work)
__releases(&pool->lock)
__acquires(&pool->lock)
{
	struct pool_workqueue *pwq = get_work_pwq(work);
	struct worker_pool *pool = worker->pool;
	bool cpu_intensive = pwq->wq->flags & WQ_CPU_INTENSIVE;
	int work_color;
	struct worker *collision;
#ifdef CONFIG_LOCKDEP
	/*
	 * It is permissible to free the struct work_struct from
	 * inside the function that is called from it, this we need to
	 * take into account for lockdep too.  To avoid bogus "held
	 * lock freed" warnings as well as problems when looking into
	 * work->lockdep_map, make a copy and use that here.
	 */
	struct lockdep_map lockdep_map;

	lockdep_copy_map(&lockdep_map, &work->lockdep_map);
#endif
	/* ensure we're on the correct CPU */
	WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
		     raw_smp_processor_id() != pool->cpu);

------------------------------------------------------------------------

Here is the splat:

------------------------------------------------------------------------

[12600.593006] WARNING: CPU: 0 PID: 6 at /home/paulmck/public_git/linux-rcu/kernel/workqueue.c:2041 process_one_work+0x46c/0x4d0
[12600.593006] Modules linked in:
[12600.593006] CPU: 0 PID: 6 Comm: mm_percpu_wq Not tainted 4.11.0-rc7+ #1
[12600.593006] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[12600.593006] Call Trace:
[12600.593006]  dump_stack+0x4f/0x72
[12600.593006]  __warn+0xc6/0xe0
[12600.593006]  warn_slowpath_null+0x18/0x20
[12600.593006]  process_one_work+0x46c/0x4d0
[12600.593006]  rescuer_thread+0x20e/0x3b0
[12600.593006]  kthread+0x104/0x140
[12600.593006]  ? worker_thread+0x4e0/0x4e0
[12600.593006]  ? kthread_create_on_node+0x40/0x40
[12600.593006]  ret_from_fork+0x29/0x40

------------------------------------------------------------------------

This happens about 3.5 hours into the TREE03 rcutorture scenario, .config
attached.

Enlightenment?

							Thanx, Paul