The safety comment on `impl Sync for Arc` references the Send safety
comment. This commit avoids that in case the two comments drift apart in
the future.
Suggested-by: Andreas Hindborg <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
Reviewed-by: Andreas Hindborg <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
---
rust/kernel/sync/arc.rs | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 87a4c9ed712b..4d10f9868d9e 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -150,9 +150,11 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Ar
// mutable reference, for example, when the reference count reaches zero and `T` is dropped.
unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
-// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the
-// same reason as above. `T` needs to be `Send` as well because a thread can clone an `&Arc<T>`
-// into an `Arc<T>`, which may lead to `T` being accessed by the same reasoning as above.
+// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync`
+// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
+// it needs `T` to be `Send` because any thread that has a `&Arc<T>` may clone it and get an
+// `Arc<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
+// example, when the reference count reaches zero and `T` is dropped.
unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
impl<T> Arc<T> {
--
2.40.1.698.g37aff9b760-goog
On Tue, 23 May 2023 14:44:16 +0000
Alice Ryhl <[email protected]> wrote:
> The safety comment on `impl Sync for Arc` references the Send safety
> comment. This commit avoids that in case the two comments drift apart in
> the future.
>
> Suggested-by: Andreas Hindborg <[email protected]>
> Signed-off-by: Alice Ryhl <[email protected]>
> Reviewed-by: Andreas Hindborg <[email protected]>
> Reviewed-by: Boqun Feng <[email protected]>
> ---
> rust/kernel/sync/arc.rs | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> index 87a4c9ed712b..4d10f9868d9e 100644
> --- a/rust/kernel/sync/arc.rs
> +++ b/rust/kernel/sync/arc.rs
> @@ -150,9 +150,11 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Ar
> // mutable reference, for example, when the reference count reaches zero and `T` is dropped.
> unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
>
> -// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the
> -// same reason as above. `T` needs to be `Send` as well because a thread can clone an `&Arc<T>`
> -// into an `Arc<T>`, which may lead to `T` being accessed by the same reasoning as above.
> +// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync`
> +// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
> +// it needs `T` to be `Send` because any thread that has a `&Arc<T>` may clone it and get an
> +// `Arc<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
> +// example, when the reference count reaches zero and `T` is dropped.
"for example" here implies that there are other case to get a mutable
reference? I don't think that's true for our `Arc` since we don't
provide a `get_mut` method.
> unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
>
> impl<T> Arc<T> {
On 5/23/23 11:44, Alice Ryhl wrote:
> The safety comment on `impl Sync for Arc` references the Send safety
> comment. This commit avoids that in case the two comments drift apart in
> the future.
>
> Suggested-by: Andreas Hindborg <[email protected]>
> Signed-off-by: Alice Ryhl <[email protected]>
> Reviewed-by: Andreas Hindborg <[email protected]>
> Reviewed-by: Boqun Feng <[email protected]>
> ---
> [...]
>
> -// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the
> -// same reason as above. `T` needs to be `Send` as well because a thread can clone an `&Arc<T>`
> -// into an `Arc<T>`, which may lead to `T` being accessed by the same reasoning as above.
> +// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync`
> +// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
> +// it needs `T` to be `Send` because any thread that has a `&Arc<T>` may clone it and get an
> +// `Arc<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
> +// example, when the reference count reaches zero and `T` is dropped.
> unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
>
> impl<T> Arc<T> {
Reviewed-by: Martin Rodriguez Reboredo <[email protected]>
On 5/23/23 17:50, Gary Guo wrote:
>> -// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the
>> -// same reason as above. `T` needs to be `Send` as well because a thread can clone an `&Arc<T>`
>> -// into an `Arc<T>`, which may lead to `T` being accessed by the same reasoning as above.
>> +// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync`
>> +// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
>> +// it needs `T` to be `Send` because any thread that has a `&Arc<T>` may clone it and get an
>> +// `Arc<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
>> +// example, when the reference count reaches zero and `T` is dropped.
>
> "for example" here implies that there are other case to get a mutable
> reference? I don't think that's true for our `Arc` since we don't
> provide a `get_mut` method.
Ah, yes, that's true. Good point.
On 5/23/23 16:44, Alice Ryhl wrote:
> The safety comment on `impl Sync for Arc` references the Send safety
> comment. This commit avoids that in case the two comments drift apart in
> the future.
>
> Suggested-by: Andreas Hindborg <[email protected]>
> Signed-off-by: Alice Ryhl <[email protected]>
> Reviewed-by: Andreas Hindborg <[email protected]>
> Reviewed-by: Boqun Feng <[email protected]>
Reviewed-by: Benno Lossin <[email protected]>
> ---
> rust/kernel/sync/arc.rs | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> index 87a4c9ed712b..4d10f9868d9e 100644
> --- a/rust/kernel/sync/arc.rs
> +++ b/rust/kernel/sync/arc.rs
> @@ -150,9 +150,11 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Ar
> // mutable reference, for example, when the reference count reaches zero and `T` is dropped.
> unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
>
> -// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the
> -// same reason as above. `T` needs to be `Send` as well because a thread can clone an `&Arc<T>`
> -// into an `Arc<T>`, which may lead to `T` being accessed by the same reasoning as above.
> +// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync`
> +// because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
> +// it needs `T` to be `Send` because any thread that has a `&Arc<T>` may clone it and get an
> +// `Arc<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
> +// example, when the reference count reaches zero and `T` is dropped.
> unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
>
> impl<T> Arc<T> {
> --
> 2.40.1.698.g37aff9b760-goog
>
--
Cheers,
Benno