linux-kernel - Re: [PATCH 0/5] V2 usb console improvements series

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Message-ID: <Pine.LNX.4.44L0.1003171132560.1734-100000@iolanthe.rowland.org>
Date:	Wed, 17 Mar 2010 11:34:57 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Jason Wessel <jason.wessel@...driver.com>
cc:	gregkh@...e.de, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/5] V2 usb console improvements series

On Wed, 17 Mar 2010, Jason Wessel wrote:

> On 03/17/2010 09:30 AM, Alan Stern wrote:
> > On Tue, 16 Mar 2010, Jason Wessel wrote:
> >
> >   
> >> Part of having the console stable requires that usb sysrq handler get
> >> executed in a tasklet.  The hcd device lock is always held while the
> >> driver call backs are executed.  The means you cannot get the sysrq
> >> printk's out to the usb console device after the in_flight urb queue
> >> is filled.
> >>     
> >
> > Either I don't understand this comment properly or else it is simply
> > wrong.  HCDs do not continue to hold their locks when handing completed
> > URBs back to drivers.  The giveback call occurs with interrupts
> > disabled, but no locks are held.
> >
> >   
> 
> The call back from the urb processing holds a lock.

Which callback and which lock, exactly?  Surely not the "hcd device
lock" as your description says, and maybe not the "driver call back".

Alan Stern

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