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* [PATCH] rust: locks: Add `get_mut` method to `Lock`
@ 2024-02-09 16:22 Mathys-Gasnier via B4 Relay
  2024-02-09 19:27 ` Martin Rodriguez Reboredo
  2024-02-09 19:44 ` Alice Ryhl
  0 siblings, 2 replies; 3+ messages in thread
From: Mathys-Gasnier via B4 Relay @ 2024-02-09 16:22 UTC (permalink / raw)
  To: Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho, Boqun Feng,
	Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
	Alice Ryhl
  Cc: rust-for-linux, linux-kernel, Mathys-Gasnier

From: Mathys-Gasnier <mathys35.gasnier@gmail.com>

Having a mutable reference guarantees that no other threads have
access to the lock, so we can take advantage of that to grant callers
access to the protected data without the the cost of acquiring and
releasing the locks. Since the lifetime of the data is tied to the
mutable reference, the borrow checker guarantees that the usage is safe.

Signed-off-by: Mathys-Gasnier <mathys35.gasnier@gmail.com>
---
 rust/kernel/sync/lock.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index f12a684bc957..7711c6313e14 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -121,6 +121,11 @@ pub fn lock(&self) -> Guard<'_, T, B> {
         // SAFETY: The lock was just acquired.
         unsafe { Guard::new(self, state) }
     }
+
+    /// Gets the data contained in the lock
+    pub fn get_mut(&mut self) -> &mut T {
+        self.data.get_mut()
+    }
 }
 
 /// A lock guard.

---
base-commit: 711cbfc717650532624ca9f56fbaf191bed56e67
change-id: 20240118-rust-locks-get-mut-c42072101d7a

Best regards,
-- 
Mathys-Gasnier <mathys35.gasnier@gmail.com>


^ permalink raw reply related	[flat|nested] 3+ messages in thread

* Re: [PATCH] rust: locks: Add `get_mut` method to `Lock`
  2024-02-09 16:22 [PATCH] rust: locks: Add `get_mut` method to `Lock` Mathys-Gasnier via B4 Relay
@ 2024-02-09 19:27 ` Martin Rodriguez Reboredo
  2024-02-09 19:44 ` Alice Ryhl
  1 sibling, 0 replies; 3+ messages in thread
From: Martin Rodriguez Reboredo @ 2024-02-09 19:27 UTC (permalink / raw)
  To: Mathys Gasnier, Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho,
	Boqun Feng, Gary Guo, Björn Roy Baron, Benno Lossin,
	Andreas Hindborg, Alice Ryhl
  Cc: rust-for-linux, linux-kernel

On 2/9/24 13:22, Mathys-Gasnier wrote:
> From: Mathys-Gasnier <mathys35.gasnier@gmail.com>
> 
> Having a mutable reference guarantees that no other threads have
> access to the lock, so we can take advantage of that to grant callers
> access to the protected data without the the cost of acquiring and
> releasing the locks. Since the lifetime of the data is tied to the
> mutable reference, the borrow checker guarantees that the usage is safe.
> 
> Signed-off-by: Mathys-Gasnier <mathys35.gasnier@gmail.com>
> ---
> [...]
> +    /// Gets the data contained in the lock

I wish that this doc comment mentioned what you've said about having a
mutable reference avoids locking, much like the documentation on
`std::sync::Mutex::get_mut`. If you do so then you can add my reviewed.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>

> +    pub fn get_mut(&mut self) -> &mut T {
> +        self.data.get_mut()
> +    }
>   }
> [...]

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] rust: locks: Add `get_mut` method to `Lock`
  2024-02-09 16:22 [PATCH] rust: locks: Add `get_mut` method to `Lock` Mathys-Gasnier via B4 Relay
  2024-02-09 19:27 ` Martin Rodriguez Reboredo
@ 2024-02-09 19:44 ` Alice Ryhl
  1 sibling, 0 replies; 3+ messages in thread
From: Alice Ryhl @ 2024-02-09 19:44 UTC (permalink / raw)
  To: mathys35.gasnier
  Cc: rust-for-linux, linux-kernel, Miguel Ojeda, Alex Gaynor,
	Wedson Almeida Filho, Boqun Feng, Gary Guo, Björn Roy Baron,
	Benno Lossin, Andreas Hindborg, Alice Ryhl

On 2/9/24 17:22, Mathys-Gasnier via B4 Relay wrote:
> From: Mathys-Gasnier <mathys35.gasnier@gmail.com>
> 
> Having a mutable reference guarantees that no other threads have
> access to the lock, so we can take advantage of that to grant callers
> access to the protected data without the the cost of acquiring and
> releasing the locks. Since the lifetime of the data is tied to the
> mutable reference, the borrow checker guarantees that the usage is safe.
> 
> Signed-off-by: Mathys-Gasnier <mathys35.gasnier@gmail.com>
> ---
>   rust/kernel/sync/lock.rs | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index f12a684bc957..7711c6313e14 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -121,6 +121,11 @@ pub fn lock(&self) -> Guard<'_, T, B> {
>           // SAFETY: The lock was just acquired.
>           unsafe { Guard::new(self, state) }
>       }
> +
> +    /// Gets the data contained in the lock
> +    pub fn get_mut(&mut self) -> &mut T {
> +        self.data.get_mut()
> +    }

You can never have a mutable reference to a Linux mutex because we pin 
our locks. At most, you can have a Pin<&mut Self>.

Alice

^ permalink raw reply	[flat|nested] 3+ messages in thread

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2024-02-09 16:22 [PATCH] rust: locks: Add `get_mut` method to `Lock` Mathys-Gasnier via B4 Relay
2024-02-09 19:27 ` Martin Rodriguez Reboredo
2024-02-09 19:44 ` Alice Ryhl

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