linux-kernel - Re: [PATCH v1 2/2] rust: Add read_poll_timeout

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <DCCF63BESWQ9.9LC8MZK7NG1Y@kernel.org>
Date: Tue, 26 Aug 2025 16:12:44 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "FUJITA Tomonori" <fujita.tomonori@...il.com>
Cc: <a.hindborg@...nel.org>, <alex.gaynor@...il.com>, <ojeda@...nel.org>,
 <aliceryhl@...gle.com>, <anna-maria@...utronix.de>,
 <bjorn3_gh@...tonmail.com>, <boqun.feng@...il.com>, <frederic@...nel.org>,
 <gary@...yguo.net>, <jstultz@...gle.com>, <linux-kernel@...r.kernel.org>,
 <lossin@...nel.org>, <lyude@...hat.com>, <rust-for-linux@...r.kernel.org>,
 <sboyd@...nel.org>, <tglx@...utronix.de>, <tmgross@...ch.edu>,
 <acourbot@...dia.com>, <daniel.almeida@...labora.com>
Subject: Re: [PATCH v1 2/2] rust: Add read_poll_timeout_atomic function

On Thu Aug 21, 2025 at 5:57 AM CEST, FUJITA Tomonori wrote:
> +pub fn read_poll_timeout_atomic<Op, Cond, T>(
> +    mut op: Op,
> +    mut cond: Cond,
> +    delay_delta: Delta,
> +    timeout_delta: Delta,
> +) -> Result<T>
> +where
> +    Op: FnMut() -> Result<T>,
> +    Cond: FnMut(&T) -> bool,
> +{
> +    let mut left_ns = timeout_delta.as_nanos();
> +    let delay_ns = delay_delta.as_nanos();
> +
> +    loop {
> +        let val = op()?;
> +        if cond(&val) {
> +            // Unlike the C version, we immediately return.
> +            // We know the condition is met so we don't need to check again.
> +            return Ok(val);
> +        }
> +
> +        if left_ns < 0 {
> +            // Unlike the C version, we immediately return.
> +            // We have just called `op()` so we don't need to call it again.
> +            return Err(ETIMEDOUT);
> +        }
> +
> +        if !delay_delta.is_zero() {
> +            udelay(delay_delta);
> +            left_ns -= delay_ns;
> +        }
> +
> +        cpu_relax();
> +        left_ns -= 1;

How do we know that each iteration costs 1ns? To make it even more obvious, we
don't control the implementation of cond(). Shouldn't we use ktime for this?