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

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Message-Id: <200810261855.47580.rjw@sisk.pl>
Date:	Sun, 26 Oct 2008 18:55:46 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Mikko C." <mikko.cal@...il.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Bug in workqueues [was: Usb devices randomly aren't detected with 2.6.28-rc1-git1]

On Sunday, 26 of October 2008, Alan Stern wrote:
> 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.

Let's make that more visible (adding CCs). :-)

Thanks,
Rafael
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