linux-kernel - Re: [PATCH v2 3/4] rust: devres: get rid of Devres' inner Arc

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Message-ID: <aFrBvwFrUGD45TeF@cassiopeiae>
Date: Tue, 24 Jun 2025 17:18:23 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, ojeda@...nel.org,
	alex.gaynor@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
	lossin@...nel.org, a.hindborg@...nel.org, aliceryhl@...gle.com,
	tmgross@...ch.edu, david.m.ertman@...el.com, ira.weiny@...el.com,
	leon@...nel.org, kwilczynski@...nel.org, bhelgaas@...gle.com,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH v2 3/4] rust: devres: get rid of Devres' inner Arc

On Sun, Jun 22, 2025 at 06:54:07PM -0700, Boqun Feng wrote:
> I think you also need to mention that `inner` only remains valid until
> `inner.devm.complete_all()` unblocks `Devres::drop()`, because after
> `Devres::drop()`'s `devm.wait_for_completion()` returns, `inner` may be
> dropped or freed.

I think of it the other way around: The invariant guarantees that `inner` is
*always* valid.

The the `drop_in_place(inner)` call has to justify that it upholds this
invariant, by ensuring that at the time it is called no other code that accesses
`inner` can ever run.

Defining it the other way around would make the `inner()` accessor unsafe.