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Date: Fri, 9 Jul 2004 11:54:11 -0700
From: Andrew Morton <akpm@osdl.org>
To: Jesse Stockall <stockall@magma.ca>
Cc: s.rivoir@gts.it, linux-kernel@vger.kernel.org,
       Alan Stern <stern@rowland.harvard.edu>
Subject: Re: 2.6.7-mm7
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Jesse Stockall <stockall@magma.ca> wrote:
>
>  + *
>  + * Unfortunately we have to use a separate wait queue, because we need
>  + * to make sure that a thread waiting for a writelock won't block other
>  + * threads from acquiring a readlock.
>    */
>   void usb_lock_all_devices(void)
>   {
>  -       down_write(&usb_all_devices_rwsem);
>  +       wait_event(usb_all_devices_wqh,
>  +                       down_write_trylock(&usb_all_devices_rwsem));

That's a bit unusual.  Could you (or Alan) please explain the reason for
this a little more?