Re: [PATCH 1/3] rust: implement `kernel::sync::Refcount`

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Oct 04, 2024 at 04:52:22PM +0100, Gary Guo wrote:
> This is a wrapping layer of `include/linux/refcount.h`. Currently only
> the most basic operations (read/set/inc/dec/dec_and_test) are implemented,
> additional methods can be implemented when they are needed.
> 
> Currently the kernel refcount has already been used in `Arc`, however it
> calls into FFI 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>
> ---
>  rust/helpers/refcount.c      | 15 ++++++
>  rust/kernel/sync.rs          |  2 +
>  rust/kernel/sync/refcount.rs | 94 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 111 insertions(+)
>  create mode 100644 rust/kernel/sync/refcount.rs
> 
> diff --git a/rust/helpers/refcount.c b/rust/helpers/refcount.c
> index f47afc148ec3..39649443426b 100644
> --- a/rust/helpers/refcount.c
> +++ b/rust/helpers/refcount.c
> @@ -8,11 +8,26 @@ refcount_t rust_helper_REFCOUNT_INIT(int n)
>  	return (refcount_t)REFCOUNT_INIT(n);
>  }
>  
> +unsigned int rust_helper_refcount_read(refcount_t *r)
> +{
> +	return refcount_read(r);
> +}

Reading a refcount is almost always a wrong thing to do (it can change
right after you read it), and I don't see any of the later patches in
this series use this call, so can you just drop this?

thanks,

greg k-h