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

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Message-Id: <20071224061220.ceed2bf8.zaitcev@redhat.com>
Date:	Mon, 24 Dec 2007 06:12:20 -0800
From:	Pete Zaitcev <zaitcev@...hat.com>
To:	Daniel Walker <dwalker@...sta.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 Sun, 23 Dec 2007 08:46:37 -0800, Daniel Walker <dwalker@...sta.com> wrote:

> 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..

The usu_lock is not held across request_module. In fact, it can be
easily taken from inside request_module, when it invokes modprobe.
Stop scaring me :-)

> 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?

Yes, it was a completition initially. But suppose you have two storage
devices, plugged in across a reboot. Two threads are created and have to
wait until the libusual's init function ends. Since we post one completion,
only one thread continues.

-- Pete
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