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Message-ID: <alpine.LNX.2.00.1003291546040.24576@pobox.suse.cz>
Date: Mon, 29 Mar 2010 15:46:59 +0200 (CEST)
From: Jiri Kosina <jkosina@...e.cz>
To: Oliver Neukum <oliver@...kum.org>
Cc: Greg KH <greg@...ah.com>, USB list <linux-usb@...r.kernel.org>,
Mauro Carvalho Chehab <mchehab@...radead.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] usb:Push BKL on open down into the drivers
On Mon, 29 Mar 2010, Oliver Neukum wrote:
> > For hiddev, this causes a problem, as you introduced BKL into
> > hiddev_connect() exactly because of the proper dependency -- we have the
> > BKL there to avoid race after usb_register_dev() -- once the device node
> > has been created, open() could happen on it.
>
> Hi,
>
> it seems to me you cannot deadlock with the BKL and an rwsem,
> as BKL will be dropped if a task blocks on the rwsem.
Ah, right you are.
> This is not a nice feature of the BKL to use. Do you have an alternative
> idea?
Not right now, without introducing additional lock into USB core or
redesigning the hiddev node registration completely. Hmmm ...
Thanks,
--
Jiri Kosina
SUSE Labs, Novell Inc.
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