linux-kernel - Re: [PATCH v2] rust: sync: add accessor for the lock behind a given guard

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Message-ID: <Z6mWnMWpAKmSjOBg@Mac.home>
Date: Sun, 9 Feb 2025 22:03:08 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rust: sync: add accessor for the lock behind a given
 guard

Hi,

On Wed, Feb 05, 2025 at 10:54:50AM +0000, Alice Ryhl wrote:
> Binder has some methods where the caller provides a lock guard, and
> Binder needs to be able to assert that the guard is associated with the
> right lock. To enable this, add an accessor to obtain a reference to the
> underlying lock that you can pass to `ptr::eq`.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> Changes in v2:
> - Rename to lock_ref() to avoid confusion with lock().
> - Rebase on v6.14-rc1.
> - Link to v1: https://lore.kernel.org/r/20250130-guard-get-lock-v1-1-8ed87899920a@google.com
> ---
>  rust/kernel/sync/lock.rs | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index eb80048e0110..8e7e6d5f61e4 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -199,7 +199,12 @@ pub struct Guard<'a, T: ?Sized, B: Backend> {
>  // SAFETY: `Guard` is sync when the data protected by the lock is also sync.
>  unsafe impl<T: Sync + ?Sized, B: Backend> Sync for Guard<'_, T, B> {}
>  
> -impl<T: ?Sized, B: Backend> Guard<'_, T, B> {
> +impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
> +    /// Returns the lock that this guard originates from.
> +    pub fn lock_ref(&self) -> &'a Lock<T, B> {
> +        self.lock
> +    }
> +
>      pub(crate) fn do_unlocked<U>(&mut self, cb: impl FnOnce() -> U) -> U {
>          // SAFETY: The caller owns the lock, so it is safe to unlock it.
>          unsafe { B::unlock(self.lock.state.get(), &self.state) };
> 
> ---
> base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
> change-id: 20250130-guard-get-lock-dd5452793d9a
> 
> Best regards,
> -- 
> Alice Ryhl <aliceryhl@...gle.com>
> 

I queued this with some changes on the commit log to make it more of an
objective tone, please see below, thanks!

Regards,
Boqun

--------------------------->8
Subject: [PATCH] rust: sync: Add accessor for the lock behind a given guard

In order to assert a particular `Guard` is associated with a particular
`Lock`, add an accessor to obtain a reference to the underlying `Lock`
of a `Guard`.

Binder needs this assertion to ensure unsafe list operations are done
with the correct lock held.

[Boqun: Capitalize the title and reword the commit log]

Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
Reviewed-by: Fiona Behrens <me@...enk.dev>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Link: https://lore.kernel.org/r/20250205-guard-get-lock-v2-1-ba32a8c1d5b7@google.com
---
 rust/kernel/sync/lock.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index eb80048e0110..8e7e6d5f61e4 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -199,7 +199,12 @@ pub struct Guard<'a, T: ?Sized, B: Backend> {
 // SAFETY: `Guard` is sync when the data protected by the lock is also sync.
 unsafe impl<T: Sync + ?Sized, B: Backend> Sync for Guard<'_, T, B> {}
 
-impl<T: ?Sized, B: Backend> Guard<'_, T, B> {
+impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
+    /// Returns the lock that this guard originates from.
+    pub fn lock_ref(&self) -> &'a Lock<T, B> {
+        self.lock
+    }
+
     pub(crate) fn do_unlocked<U>(&mut self, cb: impl FnOnce() -> U) -> U {
         // SAFETY: The caller owns the lock, so it is safe to unlock it.
         unsafe { B::unlock(self.lock.state.get(), &self.state) };
-- 
2.39.5 (Apple Git-154)