linux-kernel - Re: [Patch 3/3] Driver core: Per-subsystem multithreaded probing.

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Date:	Mon, 16 Oct 2006 12:56:13 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Duncan Sands <duncan.sands@...h.u-psud.fr>
Cc:	Greg K-H <greg@...ah.com>, Alan Stern <stern@...land.harvard.edu>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [Patch 3/3] Driver core: Per-subsystem multithreaded probing.

On Mon, 16 Oct 2006 11:13:30 +0200,
Duncan Sands <duncan.sands@...h.u-psud.fr> wrote:

> There may have been a similar problem with
> USB locking, since there too probe was expecting a lock to be held that might
> not be held when called from the kthread:
> 
> 	 * This function must be called with @dev->sem held.  When called for a
> 	 * USB interface, @dev->parent->sem must be held as well.
> 	 */
> 	int driver_probe_device(struct device_driver * drv, struct device * dev)

But as we don't know we're probing an usb interface, we have no chance
of ensuring that dev->parent->sem is taken in the multithreaded case
(meaning we couldn't do multithreaded probe for usb). (Any idea why the
parent's sem must be taken for usb interfaces?)

> Also, what about device removal racing with probe?  Is it possible for someone to
> attempt to remove a device in the gap between the call to device_attach and the
> kthread actually running and doing the probe?  That would result in remove and
> probe being called in the wrong order...

->probe won't be called if the device is already being removed, but
that still results in bus->remove being called without a prior ->probe
(but not drv->probe since dev->driver is not set at that time).
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