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Date: Wed, 18 Mar 2009 11:26:42 +0800
From: Lai Jiangshan <laijs@cn.fujitsu.com>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: Valdis.Kletnieks@vt.edu, jkosina@suse.cz, gregkh@suse.de,
       linux-kernel@vger.kernel.org, Oleg Nesterov <oleg@tv-sign.ru>,
       Oliver Neukum <oliver@neukum.org>
Subject: Re: 29-rc-mmotm - HID/USB wedge w/ WARNING: at kernel/workqueue.c:371
References: <6648.1237271589@turing-police.cc.vt.edu>	<20090317135424.9151c4f8.akpm@linux-foundation.org>	<37742.1237327272@turing-police.cc.vt.edu>	<49C05C94.7030104@cn.fujitsu.com> <20090317195004.18fb6af6.akpm@linux-foundation.org>
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Andrew Morton wrote:
> On Wed, 18 Mar 2009 10:29:40 +0800 Lai Jiangshan <laijs@cn.fujitsu.com> wrote:
> 
> 
> static void run_workqueue(struct cpu_workqueue_struct *cwq)
> {
> 	spin_lock_irq(&cwq->lock);
> 	cwq->run_depth++;
> 	if (cwq->run_depth > 3) {
> 		/* morton gets to eat his hat */
> 		printk("%s: recursion depth exceeded: %d\n",
> 			__func__, cwq->run_depth);
> 		dump_stack();
> 	}
> 
> That was added five or six years ago, and I never ever got to eat my hat.

If Valdis.Kletnieks let lockdep work, he will see the complain
from lockdep at first.

> 
>> If it's hard for you avoid flush_scheduled_work() in
>> keventd's work fuction by other fix, you can create
>> another workqueue to handle your works, IMO.
> 
> Why do we need to change anything here?  No known bugs were fixed, and some
> new ones were added.
> 

I prefer the code which has no known bugs and no known potential bugs.

I defend myself:
I did not add a new bug as you said, it's the new code hid_cease_io()
adds a new unsafe usage of workqueue.

Thanks, Lai.