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

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Message-ID: <20250428140137.468709-1-dakr@kernel.org>
Date: Mon, 28 Apr 2025 16:00:26 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: gregkh@...uxfoundation.org,
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Cc: linux-pci@...r.kernel.org,
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	Danilo Krummrich <dakr@...nel.org>
Subject: [PATCH v2 0/3] Devres optimization with bound devices

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not clear whether the data has been revoked already due to the device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.

The patches of this series are also available in [1].

[1] https://web.git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=rust/devres

Changes in v2:
  - Revocable::access(): remvoe explicit lifetimes; don't refer to 'a in
    the safety requirement
  - Devres::access()
    - rename Devres::access_with() to Devres::access()
    - add missing '```' at the end of the example
    - remove 's lifetime
    - add # Errors section

Danilo Krummrich (3):
  rust: revocable: implement Revocable::access()
  rust: devres: implement Devres::access_with()
  samples: rust: pci: take advantage of Devres::access_with()

 rust/kernel/devres.rs           | 38 +++++++++++++++++++++++++++++++++
 rust/kernel/revocable.rs        | 12 +++++++++++
 samples/rust/rust_driver_pci.rs | 12 +++++------
 3 files changed, 56 insertions(+), 6 deletions(-)

base-commit: 3be746ebc1e6e32f499a65afe405df9030153a63
-- 
2.49.0