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

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Date: Sat, 18 Nov 2023 16:32:26 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Greg KH <gregkh@...uxfoundation.org>, 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

> One example of not `Send` type (or `!Send`) is spinlock guard:
> 
> 	let guard: Guard<..> = some_lock.lock();
> 
> creating a Guard means "spin_lock()" and dropping a Guard means
> "spin_unlock()", since we cannot acquire a spinlock in one context and
> release it in another context in kernel, so `Guard<..>` is `!Send`.

Thanks for the explanation. Kernel people might have a different
meaning for context, especially in this example. We have process
context and atomic context. Process context you are allowed to sleep,
atomic context you cannot sleep. If you are in process context and
take a spinlock, you change into atomic context. And when you release
the spinlock you go back to process context. So with this meaning of
context, you do acquire the spinlock in one context, and release it in
another.

So we are going to have to think about the context the word context is
used in, and expect kernel and Rust people to maybe think of it
differently.

	Andrew