linux-kernel - Re: [PATCH 4/5] rust: hrtimer: use READ_ONCE instead of read

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Message-ID: <aV1XxWbXwkdM_AdA@google.com>
Date: Tue, 6 Jan 2026 18:43:17 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Gary Guo <gary@...yguo.net>
Cc: Andreas Hindborg <a.hindborg@...nel.org>, FUJITA Tomonori <fujita.tomonori@...il.com>, lyude@...hat.com, 
	boqun.feng@...il.com, will@...nel.org, peterz@...radead.org, 
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	rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 4/5] rust: hrtimer: use READ_ONCE instead of read_volatile

On Tue, Jan 06, 2026 at 03:23:00PM +0000, Gary Guo wrote:
> On Tue, 06 Jan 2026 13:37:34 +0100
> Andreas Hindborg <a.hindborg@...nel.org> wrote:
> 
> > "FUJITA Tomonori" <fujita.tomonori@...il.com> writes:
> > >
> > > Sorry, of course this should be:
> > >
> > > +__rust_helper ktime_t rust_helper_hrtimer_get_expires(const struct hrtimer *timer)
> > > +{
> > > +	return hrtimer_get_expires(timer);
> > > +}
> > >  
> > 
> > This is a potentially racy read. As far as I recall, we determined that
> > using read_once is the proper way to handle the situation.
> > 
> > I do not think it makes a difference that the read is done by C code.
> 
> If that's the case I think the C code should be fixed by inserting the
> READ_ONCE?

I maintain my position that if this is what you recommend C code does,
it's confusing to not make the same recommendation for Rust abstractions
to the same thing.

After all, nothing is stopping you from calling atomic_read() in C too.

Alice