netdev - Re: [PATCH net-next v7 1/5] rust: core abstractions for network PHY drivers

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Message-ID: <41e9ec99-6993-4bb4-a5e5-ade7cf4927a4@proton.me>
Date: Mon, 30 Oct 2023 08:34:46 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Boqun Feng <boqun.feng@...il.com>, FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: andrew@...n.ch, netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, tmgross@...ch.edu, miguel.ojeda.sandonis@...il.com, wedsonaf@...il.com
Subject: Re: [PATCH net-next v7 1/5] rust: core abstractions for network PHY drivers

On 30.10.23 01:19, Boqun Feng wrote:
> On Mon, Oct 30, 2023 at 07:58:52AM +0900, FUJITA Tomonori wrote:
>> if you read partially, the part might be modified by the C side during
>> reading.
> 
> If you read the part protected by phy_device->lock, C side shouldn't
> modify it, but the case here is not all fields in phy_device stay
> unchanged when phy_device->lock (and Rust side doesn't mark them
> interior mutable), see the discussion drom Andrew and me.
> 
>>
>> For me, the issue is that creating &T for an object that might be
>> modified.
> 
> The reason a `&phy_device` cannot be created here is because concurrent
> writes may cause a invalid phy_device (i.e. data race), the same applies
> to a copy.

Both comments by Boqun above are correct. Additionally even if the write
would not have a data race with the read, it would still be UB. (For example
when the write is by the same thread)

If you just read the field itself then it should be fine, since it is
protected by a lock, see Boqun's patch for manually accessing the bitfields.

But I would wait until we see a response from the bindgen devs on the issue.

-- 
Cheers,
Benno