linux-kernel - Re: [REGRESSION] 2.6.24/25: random lockups when accessing external USB harddrive

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Date:	Thu, 26 Jun 2008 10:25:35 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Stefan Becker <Stefan.Becker@...ia.com>
cc:	linux-kernel@...r.kernel.org, <linux-usb@...r.kernel.org>
Subject: Re: [REGRESSION] 2.6.24/25: random lockups when accessing external
 USB harddrive

On Thu, 26 Jun 2008, Stefan Becker wrote:

> Hi,
> 
> ext Alan Stern wrote:
> > On Wed, 25 Jun 2008, Stefan Becker wrote:
> > 
> >> HCD URB list locked by usb_hcd_link_urb_to_ep!
> >>
> >> As far as I understand the matter this only can happen if 
> >> usb_hcd_link_urb_to_ep() gets interrupted while holding the spinlock. 
> >> But according to the contract at the header of the function it should be 
> >> called with interrupts disabled!
> > 
> > So it should.  Do you know how to test whether interrupts are enabled?  
> > There's a routine called raw_irqs_disabled() defined in 
> > include/asm/irqflags.h.  Stick it inside usb_hcd_link_urb_to_ep, and 
> > the first time it returns nonzero, do a dump_stack().

Typo: I should have said "the first time it returns zero..."

Do you have any of the RT patches installed?

> Tried both and got nothing. So either our reasoning is wrong or 
> something really weird is going on. I'll try to improve my debugging 
> code and use dump_stack() at the place where it locks up.

Well, it would be pretty surprising if spin_lock_irq or 
spin_lock_irqsave were misbehaving.

Something else you should try is clearing your "owner" string just
before the spinlock is released.  You could also add a check after the
release; if the spinlock can't be locked again immediately then
something is wrong.

Alan Stern

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