When a type also implements `Sync`, the meaning of `Send` is just "this
type may be accessed mutably from threads other than the one it is
created on". That's ok for this type.
Signed-off-by: Alice Ryhl <[email protected]>
Reviewed-by: Andreas Hindborg <[email protected]>
---
rust/kernel/task.rs | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 526d29a0ae27..7eda15e5f1b3 100644
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -64,8 +64,14 @@ macro_rules! current {
#[repr(transparent)]
pub struct Task(pub(crate) Opaque<bindings::task_struct>);
-// SAFETY: It's OK to access `Task` through references from other threads because we're either
-// accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
+// SAFETY: By design, the only way to access a `Task` is via the `current` function or via an
+// `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in
+// which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor
+// runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`.
+unsafe impl Send for Task {}
+
+// SAFETY: It's OK to access `Task` through shared references from other threads because we're
+// either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
// synchronised by C code (e.g., `signal_pending`).
unsafe impl Sync for Task {}
--
2.40.1.698.g37aff9b760-goog
On Tue, 23 May 2023 14:44:18 +0000
Alice Ryhl <[email protected]> wrote:
> When a type also implements `Sync`, the meaning of `Send` is just "this
> type may be accessed mutably from threads other than the one it is
> created on". That's ok for this type.
>
> Signed-off-by: Alice Ryhl <[email protected]>
> Reviewed-by: Andreas Hindborg <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
> ---
> rust/kernel/task.rs | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
> index 526d29a0ae27..7eda15e5f1b3 100644
> --- a/rust/kernel/task.rs
> +++ b/rust/kernel/task.rs
> @@ -64,8 +64,14 @@ macro_rules! current {
> #[repr(transparent)]
> pub struct Task(pub(crate) Opaque<bindings::task_struct>);
>
> -// SAFETY: It's OK to access `Task` through references from other threads because we're either
> -// accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
> +// SAFETY: By design, the only way to access a `Task` is via the `current` function or via an
> +// `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in
> +// which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor
> +// runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`.
> +unsafe impl Send for Task {}
> +
> +// SAFETY: It's OK to access `Task` through shared references from other threads because we're
> +// either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
> // synchronised by C code (e.g., `signal_pending`).
> unsafe impl Sync for Task {}
>
On 5/23/23 11:44, Alice Ryhl wrote:
> When a type also implements `Sync`, the meaning of `Send` is just "this
> type may be accessed mutably from threads other than the one it is
> created on". That's ok for this type.
>
> Signed-off-by: Alice Ryhl <[email protected]>
> Reviewed-by: Andreas Hindborg <[email protected]>
> ---
> [...]
>
> -// SAFETY: It's OK to access `Task` through references from other threads because we're either
> -// accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
> +// SAFETY: By design, the only way to access a `Task` is via the `current` function or via an
> +// `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in
> +// which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor
> +// runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`.
> +unsafe impl Send for Task {}
> +
> +// SAFETY: It's OK to access `Task` through shared references from other threads because we're
> +// either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
> // synchronised by C code (e.g., `signal_pending`).
> unsafe impl Sync for Task {}
>
Reviewed-by: Martin Rodriguez Reboredo <[email protected]>
On 5/23/23 16:44, Alice Ryhl wrote:
> When a type also implements `Sync`, the meaning of `Send` is just "this
> type may be accessed mutably from threads other than the one it is
> created on". That's ok for this type.
>
> Signed-off-by: Alice Ryhl <[email protected]>
> Reviewed-by: Andreas Hindborg <[email protected]>
Reviewed-by: Benno Lossin <[email protected]>
> ---
> rust/kernel/task.rs | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
> index 526d29a0ae27..7eda15e5f1b3 100644
> --- a/rust/kernel/task.rs
> +++ b/rust/kernel/task.rs
> @@ -64,8 +64,14 @@ macro_rules! current {
> #[repr(transparent)]
> pub struct Task(pub(crate) Opaque<bindings::task_struct>);
>
> -// SAFETY: It's OK to access `Task` through references from other threads because we're either
> -// accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
> +// SAFETY: By design, the only way to access a `Task` is via the `current` function or via an
> +// `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in
> +// which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor
> +// runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`.
> +unsafe impl Send for Task {}
> +
> +// SAFETY: It's OK to access `Task` through shared references from other threads because we're
> +// either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
> // synchronised by C code (e.g., `signal_pending`).
> unsafe impl Sync for Task {}
>
> --
> 2.40.1.698.g37aff9b760-goog
>
--
Cheers,
Benno