linux-kernel - Re: [PATCH] rust: device: fix device context of Device::parent()

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Message-Id: <DDK9BL9MOTUI.359BJBMHFTFXU@nvidia.com>
Date: Fri, 17 Oct 2025 11:55:07 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Danilo Krummrich" <dakr@...nel.org>, <gregkh@...uxfoundation.org>,
 <rafael@...nel.org>, <david.m.ertman@...el.com>, <ira.weiny@...el.com>,
 <leon@...nel.org>, <ojeda@...nel.org>, <alex.gaynor@...il.com>,
 <boqun.feng@...il.com>, <gary@...yguo.net>, <bjorn3_gh@...tonmail.com>,
 <lossin@...nel.org>, <a.hindborg@...nel.org>, <aliceryhl@...gle.com>,
 <tmgross@...ch.edu>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <stable@...r.kernel.org>
Subject: Re: [PATCH] rust: device: fix device context of Device::parent()

On Thu Oct 16, 2025 at 10:31 PM JST, Danilo Krummrich wrote:
> Regardless of the DeviceContext of a device, we can't give any
> guarantees about the DeviceContext of its parent device.
>
> This is very subtle, since it's only caused by a simple typo, i.e.
>
> 	 Self::from_raw(parent)
>
> which preserves the DeviceContext in this case, vs.
>
> 	 Device::from_raw(parent)
>
> which discards the DeviceContext.
>
> (I should have noticed it doing the correct thing in auxiliary::Device
> subsequently, but somehow missed it.)
>
> Hence, fix both Device::parent() and auxiliary::Device::parent().
>
> Cc: stable@...r.kernel.org
> Fixes: a4c9f71e3440 ("rust: device: implement Device::parent()")
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>

Ouch, that will make me think twice the next time I consider using
`Self` for convenience... :)

Reviewed-by: Alexandre Courbot <acourbot@...dia.com>