Re: [PATCH 3/3] rust: block: convert `block::mq` to use `Refcount`

[Dirk Behme <dirk.behme@gmail.com>]

Am 04.10.24 um 17:52 schrieb Gary Guo:
> Currently there's a custom reference counting in `block::mq`, which uses
> `AtomicU64` Rust atomics, and this type doesn't exist on some 32-bit
> architectures. We cannot just change it to use 32-bit atomics, because
> doing so will make it vulnerable to refcount overflow. So switch it to
> use the kernel refcount `kernel::sync::Refcount` instead.
> 
> There is an operation needed by `block::mq`, atomically decreasing
> refcount from 2 to 0, which is not available through refcount.h, so
> I exposed `Refcount::as_atomic` which allows accessing the refcount
> directly.
> 
> Cc: Will Deacon <will@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> ---
...
> diff --git a/rust/kernel/block/mq/request.rs b/rust/kernel/block/mq/request.rs
> index a0e22827f3f4..7b63c02bdce7 100644
> --- a/rust/kernel/block/mq/request.rs
> +++ b/rust/kernel/block/mq/request.rs
....
> @@ -37,6 +38,9 @@
>   /// We need to track C and D to ensure that it is safe to end the request and hand
>   /// back ownership to the block layer.
>   ///
> +/// Note that driver can still obtain new `ARef` even there is no `ARef`s in existence by using

Do you like to check this sentence? Maybe:

Note that "a" driver can still obtain "a" new `ARef` even "if" there 
"are" no `ARef`s in existence by using ....

?

Best regards

Dirk