linux-kernel - Re: [PATCH 1/5] nubus: Simplify check in remove callback

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Message-ID: <20210731120515.xkr64yvnczchxz4s@pengutronix.de>
Date:   Sat, 31 Jul 2021 14:05:15 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Finn Thain <fthain@...ux-m68k.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: [PATCH 1/5] nubus: Simplify check in remove callback

Hello Finn,

On Sat, Jul 31, 2021 at 08:32:38PM +1000, Finn Thain wrote:
> On Tue, 27 Jul 2021, Uwe Kleine-König wrote:
> > On Tue, Jul 27, 2021 at 07:50:39PM +1000, Finn Thain wrote:
> > > On Tue, 27 Jul 2021, Uwe Kleine-König wrote:
> > > 
> > > > The driver core only calls a remove callback when the device was 
> > > > successfully bound (aka probed) before. So dev->driver is never 
> > > > NULL.
> > > 
> > > Are you sure dev->driver is non-NULL for the lifetime of the device? A 
> > > quick glance at device_reprobe() makes me wonder about that.
> > 
> > Not for the lifetime of the device, but as long as a driver is bound to 
> > the device. device_reprobe() calls device_driver_detach() after which 
> > the driver is considered unbound and dev->driver is assigned NULL. (via 
> > device_driver_detach -> device_release_driver_internal -> 
> > __device_release_driver)
> 
> Are you saying that this situation does not presently apply to nubus, 
> zorro or superhyway? Or are you saying that the remove callback will never 
> be called in this situation?

I'm saying that if you call device_reprobe() the remove callback is
called before dev->driver becomes NULL. So in the remove callback it's
safe to assume that dev->driver is non-NULL.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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