netdev - Re: [PATCH net-next v7 1/5] rust: core abstractions for network PHY drivers

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Date: Fri, 17 Nov 2023 14:50:45 -0500
From: Greg KH <gregkh@...uxfoundation.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: Alice Ryhl <aliceryhl@...gle.com>, fujita.tomonori@...il.com,
	benno.lossin@...ton.me, miguel.ojeda.sandonis@...il.com,
	netdev@...r.kernel.org, rust-for-linux@...r.kernel.org,
	tmgross@...ch.edu, wedsonaf@...il.com
Subject: Re: [PATCH net-next v7 1/5] rust: core abstractions for network PHY
 drivers

On Fri, Nov 17, 2023 at 02:53:44PM +0100, Andrew Lunn wrote:
> > I would change this to "it's okay to call phy_drivers_unregister from a
> > different thread than the one in which phy_drivers_register was called".
> 
> This got me thinking about 'threads'. For register and unregister, we
> are talking abut the kernel modules module_init() and module_exit()
> function. module_init() can be called before user space is even
> started, but it could also be called by insmod. module_exit() could be
> called by rmmod, but it could also be the kernel, after user space has
> gone away on shutdown.

The kernel will not call module_exit() on shutdown.  Or has something
changed recently?

> We are always in a context which can block, but
> i never really think of this being threads. You can start a kernel
> thread, and have some data structure exclusively used by that kernel
> thread, but that is pretty unusual.
> 
> So i would probably turn this commenting around. Only comment like
> this in the special case that a kernel thread exists, and it is
> expected to have exclusive access.

With the driver model, you can be sure that your probe/release functions
for the bus will never be called at the same time, and module_init/exit
can never be called at the same time, so perhaps this isn't an issue?

thanks,

greg k-h