linux-kernel - Bug in workqueues [was: Usb devices randomly aren't detected with 2.6.28-rc1-git1]

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Message-ID: <Pine.LNX.4.44L0.0810261327170.25044-100000@netrider.rowland.org>
Date:	Sun, 26 Oct 2008 13:34:00 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Mikko C." <mikko.cal@...il.com>
cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>
Subject: Bug in workqueues [was: Usb devices randomly aren't detected with
 2.6.28-rc1-git1]

This is no longer a USB issue, so I'm asking for help from the general 
kernel community.  Background can be found in Bugzilla #11853.

On Sun, 26 Oct 2008, Mikko C. wrote:

> Mikko C. ha scritto:
> > Alan Stern ha scritto:
> >>
> >> I don't see anything in there that looks particularly suspicious.  
> >> The nature of your errors suggests that the default workqueue has 
> >> crashed or hung, but it shows up okay in the dump.  Are you sure this 
> >> dump was made when the devices failed to appear?
> >>
> >>  
> >
> > Yes, I'm 100% sure.
> >
> >> What happens when you try to rmmod the ALSA modules?  Does rmmod 
> >> crash with an error or does it hang?  If it hangs, can you get 
> >> another task dump showing the hanging process?
> >>   
> >
> > Whenever I try rmmoding something, it hangs (no crash) and I'm not 
> > able to do anything, beside moving the mouse.
> > I posted here: http://marc.info/?l=linux-kernel&m=122502213503239&w=4
> > but that's probably not enough, so I will try getting a full dump.
> >
> Here it is: http://bugzilla.kernel.org/attachment.cgi?id=18452&action=view

The task dump shows rmmod waiting for flush_workqueue().  But the 
events/0 task doesn't appear to be hung, and the task dump taken before 
running rmmod shows events/0 doing something different.

So apparently flush_workqueue() isn't working.

Alan Stern

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