linux-kernel - Re: [PATCH 4/4] usb: libusual: locking cleanup

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Message-Id: <1198428397.2742.20.camel@imap.mvista.com>
Date:	Sun, 23 Dec 2007 08:46:37 -0800
From:	Daniel Walker <dwalker@...sta.com>
To:	Pete Zaitcev <zaitcev@...hat.com>
Cc:	akpm@...ux-foundation.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org, linux@...mer.net,
	jonathan@...masters.org, matthias.kaehlcke@...il.com,
	kjwinchester@...il.com
Subject: Re: [PATCH 4/4] usb: libusual: locking cleanup

On Sat, 2007-12-22 at 23:37 -0800, Pete Zaitcev wrote:
> On Sat, 22 Dec 2007 09:01:50 -0800, Daniel Walker <dwalker@...sta.com> wrote:
> 
> > Then in usu_probe_thread() your basically stopping it at the start of
> > the function with a down(), and the up() is just ancillary .. So you
> > could easily move the up() further down in the function and still have
> > the same level of exclusion.. 
> 
> The unfortunate complication here is request_module. I didn't want to
> keep a semaphore locked across it, in case child waits for something.
> I wonder if there may be some deadlock that we cannot foresee.
> But I guess it won't hurt to try.

I noticed you also have a spinlock held in usu_probe_thread(), the
usu_lock.. That spinlock would preclude anything inside request_module()
from sleeping..

One thing that has bothered me is that I don't see a reason why this
couldn't become a complete, yet you have a comment which says that it
can't be a complete.. I honestly didn't understand the comment.. I would
imagine that you tried a complete , and it didn't work?

> I tested the patch and it seems to work ok.

Great, thanks ..

Daniel

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