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Date: Sat, 26 Mar 2022 14:04:30 +0100 From: Lukas Wunner <lukas@...ner.de> To: Andrew Lunn <andrew@...n.ch> Cc: Oleksij Rempel <o.rempel@...gutronix.de>, Oliver Neukum <oneukum@...e.com>, Oleksij Rempel <linux@...pel-privat.de>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Heiner Kallweit <hkallweit1@...il.com> Subject: Re: ordering of call to unbind() in usbnet_disconnect On Sat, Mar 26, 2022 at 01:49:28PM +0100, Andrew Lunn wrote: > On Sat, Mar 26, 2022 at 01:39:29PM +0100, Lukas Wunner wrote: > > On Mon, Mar 21, 2022 at 02:10:27PM +0100, Andrew Lunn wrote: > > > There are two patterns in use at the moment: > > > > > > 1) The phy is attached in open() and detached in close(). There is no > > > danger of the netdev disappearing at this time. > > > > > > 2) The PHY is attached during probe, and detached during release. > > > > > > This second case is what is being used here in the USB code. This is > > > also a common pattern for complex devices. In probe, you get all the > > > components of a complex devices, stitch them together and then > > > register the composite device. During release, you unregister the > > > composite device, and then release all the components. Since this is a > > > natural model, i think it should work. > > > > I've gone through all drivers and noticed that some of them use a variation > > of pattern 2 which looks fishy: > > > > On probe, they first attach the PHY, then register the netdev. > > On remove, they detach the PHY, then unregister the netdev. > > > > Is it legal to detach the PHY from a registered (potentially running) > > netdev? It looks wrong to me. > > I think the network stack guarantee that the close() method is called > before unregister completes. It is a common pattern to attach the PHY > in open() and detach it in close(). The stack itself should not be > using the PHY when it is down, the exception being IOCTL handlers > which people often get wrong. But the PHY is detached from a *running* netdev *before* that netdev is unregistered (and closed). Is that really legal? Thanks, Lukas
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