linux-kernel - Re: [PATCH] driver core: unbind consumers before locking parent on device unbind

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Message-ID: <1487357213.13536.60.camel@pengutronix.de>
Date:   Fri, 17 Feb 2017 19:46:53 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, patchwork-lst@...gutronix.de,
        kernel@...gutronix.de
Subject: Re: [PATCH] driver core: unbind consumers before locking parent on
 device unbind

Am Freitag, den 17.02.2017, 10:42 -0800 schrieb Greg Kroah-Hartman:
> On Fri, Feb 17, 2017 at 07:36:29PM +0100, Lucas Stach wrote:
> > On forced unbind the parent lock is taken, as the device might be a USB
> > device. The device to be unbound might have active consumers, which
> > must be unbound before calling device_release_driver(), otherwise this
> > function might deadlock when trying to take the parent lock during
> > consumer unbind.
> 
> Really?  What type of device does this fail on today?

Regular devices on a MMIO bus. __device_release_driver() will take the
parent lock unconditionally when it unbinds consumer devices. So if the
forced unbound device is on the same bus as the consumer we will
deadlock right there.

Regards,
Lucas