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From: Duncan Sands <baldrick@free.fr>
To: Oliver Neukum <oliver@neukum.org>, Alan Stern <stern@rowland.harvard.edu>
Subject: Re: [linux-usb-devel] Re: [OOPS,  usbcore, releaseintf] 2.6.0-test10-mm1
Date: Thu, 11 Dec 2003 10:45:11 +0100
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Cc: David Brownell <david-b@pacbell.net>, Vince <fuzzy77@free.fr>,
       "Randy.Dunlap" <rddunlap@osdl.org>, <mfedyk@matchmail.com>,
       <zwane@holomorphy.com>, <linux-kernel@vger.kernel.org>,
       USB development list <linux-usb-devel@lists.sourceforge.net>
References: <Pine.LNX.4.44L0.0312081754480.2034-100000@ida.rowland.org> <200312101749.17173.baldrick@free.fr> <200312101758.02334.oliver@neukum.org>
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> > > > __usb_set_configuration - lockless version
> > > > usb_set_configuration - locked version
> > >
> > > Partially done.
> > > That's what the _physical version of usb_reset_device() is about.
> >
> > Unfortunately, usb_physical_reset_device calls usb_set_configuration
> > which takes dev->serialize.
>
> That is bad, but the solution is obvious.
> All such operations need a _physical version.
> At first sight this may look less elegant than some lock dropping schemes,
> but it is a solution that produces obviously correct code paths with
> respect to locking.

Hi Oliver, I agree, except that there are several layers of locking: dev->serialize
but also the bus rwsem.  So does "physical" mean no subsys.rwsem or no
dev->serialize or both?

Ciao, Duncan.

int usb_reset_device(struct usb_device *udev)
{
        struct device *gdev = &udev->dev;
        int r;

        down_read(&gdev->bus->subsys.rwsem);
        r = usb_physical_reset_device(udev);
        up_read(&gdev->bus->subsys.rwsem);

        return r;
}