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[2003:df:bf2f:2200:c8eb:5450:fddc:5d96]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5c8e05f450csm48681a12.97.2024.10.04.09.43.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Oct 2024 09:43:58 -0700 (PDT) Message-ID: <9629a9d2-7e79-41ae-96c9-5fb26493c37a@gmail.com> Date: Fri, 4 Oct 2024 18:43:57 +0200 Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/3] rust: block: convert `block::mq` to use `Refcount` To: Gary Guo , Andreas Hindborg , Boqun Feng , Miguel Ojeda , Alex Gaynor , =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Alice Ryhl , Trevor Gross , Jens Axboe Cc: Will Deacon , Peter Zijlstra , Mark Rutland , linux-block@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org References: <20241004155247.2210469-1-gary@garyguo.net> <20241004155247.2210469-4-gary@garyguo.net> Content-Language: de-AT-frami From: Dirk Behme In-Reply-To: <20241004155247.2210469-4-gary@garyguo.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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 > Cc: Peter Zijlstra > Cc: Boqun Feng > Cc: Mark Rutland > Signed-off-by: Gary Guo > --- ... > 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