linux-kernel - Re: 29-rc-mmotm - HID/USB wedge w/ WARNING: at kernel/workqueue.c:371

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Message-Id: <20090317195004.18fb6af6.akpm@linux-foundation.org>
Date:	Tue, 17 Mar 2009 19:50:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Valdis.Kletnieks@...edu, jkosina@...e.cz, gregkh@...e.de,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...sign.ru>,
	Oliver Neukum <oliver@...kum.org>
Subject: Re: 29-rc-mmotm - HID/USB wedge w/ WARNING: at
 kernel/workqueue.c:371

On Wed, 18 Mar 2009 10:29:40 +0800 Lai Jiangshan <laijs@...fujitsu.com> wrote:

> Valdis.Kletnieks@...edu wrote:
> > On Tue, 17 Mar 2009 13:54:24 PDT, Andrew Morton said:
> > 
> >> It's an error in workqueue-avoid-recursion-in-run_workqueue.patch, methinks.
> > 
> > Thanks for the diagnosis - I got as far as realizing that any backtrace that
> > included flush_cpu_workqueue() and worker_thread() had a problem and got
> > stuck there.
> > 
> 
> It's dangerous when we allow recursion in run_workqueue().

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 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.

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