diff mbox series

[v2,01/13] rust: sync: introduce `LockClassKey`

Message ID 20230405175111.5974-1-wedsonaf@gmail.com
State New
Headers
Series [v2,01/13] rust: sync: introduce `LockClassKey` |

Commit Message

Wedson Almeida Filho April 5, 2023, 5:50 p.m. UTC 
  From: Wedson Almeida Filho <walmeida@microsoft.com>

It is a wrapper around C's `lock_class_key`, which is used by the
synchronisation primitives that are checked with lockdep. This is in
preparation for introducing Rust abstractions for these primitives.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
---
v1 -> v2: Fixed a typo in comment

 rust/kernel/sync.rs | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

Comments

Greg KH April 5, 2023, 6 p.m. UTC | #1 
On Wed, Apr 05, 2023 at 02:50:59PM -0300, Wedson Almeida Filho wrote:
> From: Wedson Almeida Filho <walmeida@microsoft.com>
> 
> It is a wrapper around C's `lock_class_key`, which is used by the
> synchronisation primitives that are checked with lockdep. This is in
> preparation for introducing Rust abstractions for these primitives.
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> ---
> v1 -> v2: Fixed a typo in comment
> 
>  rust/kernel/sync.rs | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
> 
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 33da23e3076d..84a4b560828c 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -5,6 +5,51 @@
>  //! This module contains the kernel APIs related to synchronisation that have been ported or
>  //! wrapped for usage by Rust code in the kernel.
>  
> +use crate::types::Opaque;
> +
>  mod arc;
>  
>  pub use arc::{Arc, ArcBorrow, UniqueArc};
> +
> +/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
> +#[repr(transparent)]
> +pub struct LockClassKey(Opaque<bindings::lock_class_key>);

Will this disappear into "nothing" if lockdep is disabled in the build?

If not, it should, if so, I couldn't see where that option was, sorry
for the noise.

thanks,

greg k-h
Wedson Almeida Filho April 5, 2023, 8:05 p.m. UTC | #2 
On Wed, Apr 05, 2023 at 08:00:15PM +0200, Greg KH wrote:
> On Wed, Apr 05, 2023 at 02:50:59PM -0300, Wedson Almeida Filho wrote:
> > From: Wedson Almeida Filho <walmeida@microsoft.com>
> > 
> > +/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
> > +#[repr(transparent)]
> > +pub struct LockClassKey(Opaque<bindings::lock_class_key>);
> 
> Will this disappear into "nothing" if lockdep is disabled in the build?
> 
> If not, it should, if so, I couldn't see where that option was, sorry
> for the noise.

Yeah, the C definition of lock_class_key is an empty struct, which is a
zero-sized type. So instances of this type will occupy 0 bytes.

We'll still have the cost of passing pointers from Rust to C of instances of
this type, which we could add an alternate version (dependent on lockdep being
enabled or not) in Rust to avoid, but since it will be optimised away when LTO
is enabled and doesn't add up to much when LTO is disabled, we chose the simpler
option of having a single implementation.
Gary Guo April 5, 2023, 8:21 p.m. UTC | #3 
On Wed,  5 Apr 2023 14:50:59 -0300
Wedson Almeida Filho <wedsonaf@gmail.com> wrote:

> From: Wedson Almeida Filho <walmeida@microsoft.com>
> 
> It is a wrapper around C's `lock_class_key`, which is used by the
> synchronisation primitives that are checked with lockdep. This is in
> preparation for introducing Rust abstractions for these primitives.
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> ---
> v1 -> v2: Fixed a typo in comment
> 
>  rust/kernel/sync.rs | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
> 
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 33da23e3076d..84a4b560828c 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -5,6 +5,51 @@
>  //! This module contains the kernel APIs related to synchronisation that have been ported or
>  //! wrapped for usage by Rust code in the kernel.
>  
> +use crate::types::Opaque;
> +
>  mod arc;
>  
>  pub use arc::{Arc, ArcBorrow, UniqueArc};
> +
> +/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
> +#[repr(transparent)]
> +pub struct LockClassKey(Opaque<bindings::lock_class_key>);
> +
> +// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
> +// provides its own synchronization.
> +unsafe impl Sync for LockClassKey {}
> +
> +impl LockClassKey {
> +    /// Creates a new lock class key.
> +    pub const fn new() -> Self {
> +        Self(Opaque::uninit())
> +    }
> +
> +    #[allow(dead_code)]
> +    pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
> +        self.0.get()
> +    }
> +}
> +
> +/// Defines a new static lock class and returns a pointer to it.
> +#[doc(hidden)]
> +#[macro_export]
> +macro_rules! static_lock_class {
> +    () => {{
> +        static CLASS: $crate::sync::LockClassKey = $crate::sync::LockClassKey::new();
> +        &CLASS
> +    }};
> +}
> +
> +/// Returns the given string, if one is provided, otherwise generates one based on the source code
> +/// location.
> +#[doc(hidden)]
> +#[macro_export]
> +macro_rules! optional_name {
> +    () => {
> +        $crate::c_str!(core::concat!(core::file!(), ":", core::line!()))

nit: prefer `::core` to `core` in macro.

> +    };
> +    ($name:literal) => {
> +        $crate::c_str!($name)
> +    };
> +}
diff mbox series

Patch

diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index 33da23e3076d..84a4b560828c 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -5,6 +5,51 @@ 
 //! This module contains the kernel APIs related to synchronisation that have been ported or
 //! wrapped for usage by Rust code in the kernel.
 
+use crate::types::Opaque;
+
 mod arc;
 
 pub use arc::{Arc, ArcBorrow, UniqueArc};
+
+/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
+#[repr(transparent)]
+pub struct LockClassKey(Opaque<bindings::lock_class_key>);
+
+// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
+// provides its own synchronization.
+unsafe impl Sync for LockClassKey {}
+
+impl LockClassKey {
+    /// Creates a new lock class key.
+    pub const fn new() -> Self {
+        Self(Opaque::uninit())
+    }
+
+    #[allow(dead_code)]
+    pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
+        self.0.get()
+    }
+}
+
+/// Defines a new static lock class and returns a pointer to it.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! static_lock_class {
+    () => {{
+        static CLASS: $crate::sync::LockClassKey = $crate::sync::LockClassKey::new();
+        &CLASS
+    }};
+}
+
+/// Returns the given string, if one is provided, otherwise generates one based on the source code
+/// location.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! optional_name {
+    () => {
+        $crate::c_str!(core::concat!(core::file!(), ":", core::line!()))
+    };
+    ($name:literal) => {
+        $crate::c_str!($name)
+    };
+}