linux-kernel - Re: [PATCH v2 0/3] Devres optimization with bound devices

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Message-Id: <D9JMO1USPIAB.3TBU959NO7P9M@nvidia.com>
Date: Wed, 30 Apr 2025 11:46:04 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Danilo Krummrich" <dakr@...nel.org>, <gregkh@...uxfoundation.org>,
 <rafael@...nel.org>, <bhelgaas@...gle.com>, <kwilczynski@...nel.org>,
 <zhiw@...dia.com>, <cjia@...dia.com>, <jhubbard@...dia.com>,
 <bskeggs@...dia.com>, <acurrid@...dia.com>, <joelagnelf@...dia.com>,
 <ttabi@...dia.com>, <ojeda@...nel.org>, <alex.gaynor@...il.com>,
 <boqun.feng@...il.com>, <gary@...yguo.net>, <bjorn3_gh@...tonmail.com>,
 <benno.lossin@...ton.me>, <a.hindborg@...nel.org>, <aliceryhl@...gle.com>,
 <tmgross@...ch.edu>
Cc: <linux-pci@...r.kernel.org>, <rust-for-linux@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/3] Devres optimization with bound devices

On Mon Apr 28, 2025 at 11:00 PM JST, Danilo Krummrich wrote:
> This patch series implements a direct accessor for the data stored within
> a Devres container for cases where we can prove that we own a reference
> to a Device<Bound> (i.e. a bound device) of the same device that was used
> to create the corresponding Devres container.
>
> Usually, when accessing the data stored within a Devres container, it is
> not clear whether the data has been revoked already due to the device
> being unbound and, hence, we have to try whether the access is possible
> and subsequently keep holding the RCU read lock for the duration of the
> access.
>
> However, when we can prove that we hold a reference to Device<Bound>
> matching the device the Devres container has been created with, we can
> guarantee that the device is not unbound for the duration of the
> lifetime of the Device<Bound> reference and, hence, it is not possible
> for the data within the Devres container to be revoked.
>
> Therefore, in this case, we can bypass the atomic check and the RCU read
> lock, which is a great optimization and simplification for drivers.

Thanks, this removes one of my pain points with the way revocable
resources were accessed and will allow to write drivers in a much more
natural way.

FWIW, the series

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