linux-kernel - Re: [PATCH 6/6] workqueue: reimplement WQ_HIGHPRI using a separate worker

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Message-ID: <20120712214514.GD20167@google.com>
Date:	Thu, 12 Jul 2012 14:45:14 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	joshhunt00@...il.com, axboe@...nel.dk, rni@...gle.com,
	vgoyal@...hat.com, vwadekar@...dia.com,
	herbert@...dor.apana.org.au, davem@...emloft.net,
	linux-crypto@...r.kernel.org, swhiteho@...hat.com, bpm@....com,
	elder@...nel.org, xfs@....sgi.com, marcel@...tmann.org,
	gustavo@...ovan.org, johan.hedberg@...il.com,
	linux-bluetooth@...r.kernel.org, martin.petersen@...cle.com,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 6/6] workqueue: reimplement WQ_HIGHPRI using a separate
 worker_pool

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;
--
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