Re: [PATCH 6/6] workqueue: reimplement WQ_HIGHPRI using a separate worker_pool

Tejun Heo
2012-07-12T21:45:20Z

Hello, again.

On Thu, Jul 12, 2012 at 10:05:19AM -0700, Tejun Heo wrote:
> On Thu, Jul 12, 2012 at 09:06:48PM +0800, Fengguang Wu wrote:
> > [ 0.207977] WARNING: at /c/kernel-tests/mm/kernel/workqueue.c:1217 worker_enter_idle+0x2b8/0x32b()
> > [ 0.207977] Modules linked in:
> > [ 0.207977] Pid: 1, comm: swapper/0 Not tainted 3.5.0-rc6-08414-g9645fff #15
> > [ 0.207977] Call Trace:
> > [ 0.207977] [<ffffffff81087189>] ? worker_enter_idle+0x2b8/0x32b
> > [ 0.207977] [<ffffffff810559d9>] warn_slowpath_common+0xae/0xdb
> > [ 0.207977] [<ffffffff81055a2e>] warn_slowpath_null+0x28/0x31
> > [ 0.207977] [<ffffffff81087189>] worker_enter_idle+0x2b8/0x32b
> > [ 0.207977] [<ffffffff81087222>] start_worker+0x26/0x42
> > [ 0.207977] [<ffffffff81c8b261>] init_workqueues+0x2d2/0x59a
> > [ 0.207977] [<ffffffff81c8af8f>] ? usermodehelper_init+0x8a/0x8a
> > [ 0.207977] [<ffffffff81000284>] do_one_initcall+0xce/0x272
> > [ 0.207977] [<ffffffff81c6f650>] kernel_init+0x12e/0x3c1
> > [ 0.207977] [<ffffffff814b9b74>] kernel_thread_helper+0x4/0x10
> > [ 0.207977] [<ffffffff814b80b0>] ? retint_restore_args+0x13/0x13
> > [ 0.207977] [<ffffffff81c6f522>] ? start_kernel+0x737/0x737
> > [ 0.207977] [<ffffffff814b9b70>] ? gs_change+0x13/0x13
>
> Yeah, I forgot to flip the WARN_ON_ONCE() condition so that it checks
> nr_running before looking at pool->nr_running. The warning is
> spurious. Will post fix soon.

I was wrong and am now dazed and confused. That's from
init_workqueues() where only cpu0 is running. How the hell did
nr_running manage to become non-zero at that point? Can you please
apply the following patch and report the boot log? Thank you.

---
kernel/workqueue.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -699,8 +699,10 @@ void wq_worker_waking_up(struct task_str
{
struct worker *worker = kthread_data(task);

- if (!(worker->flags & WORKER_NOT_RUNNING))
+ if (!(worker->flags & WORKER_NOT_RUNNING)) {
+ WARN_ON_ONCE(cpu != worker->pool->gcwq->cpu);
atomic_inc(get_pool_nr_running(worker->pool));
+ }
}

/**
@@ -730,6 +732,7 @@ struct task_struct *wq_worker_sleeping(s

/* this can only happen on the local cpu */
BUG_ON(cpu != raw_smp_processor_id());
+ WARN_ON_ONCE(cpu != worker->pool->gcwq->cpu);

/*
* The counterpart of the following dec_and_test, implied mb,
@@ -3855,6 +3858,10 @@ static int __init init_workqueues(void)
for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++)
INIT_HLIST_HEAD(&gcwq->busy_hash[i]);

+ if (cpu != WORK_CPU_UNBOUND)
+ printk("XXX cpu=%d gcwq=%p base=%p\n", cpu, gcwq,
+ per_cpu_ptr(&pool_nr_running, cpu));
+
for_each_worker_pool(pool, gcwq) {
pool->gcwq = gcwq;
INIT_LIST_HEAD(&pool->worklist);
@@ -3868,6 +3875,10 @@ static int __init init_workqueues(void)
(unsigned long)pool);

ida_init(&pool->worker_ida);
+
+ printk("XXX cpu=%d nr_running=%d @ %p\n", gcwq->cpu,
+ atomic_read(get_pool_nr_running(pool)),
+ get_pool_nr_running(pool));
}

gcwq->trustee_state = TRUSTEE_DONE;