linux-kernel - Re: C aggregate passing (Rust kernel policy)

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Message-ID: <20250226165619.64998576@gandalf.local.home>
Date: Wed, 26 Feb 2025 16:56:19 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Martin Uecker <uecker@...raz.at>, Ralf Jung <post@...fj.de>, "Paul E.
 McKenney" <paulmck@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, Ventura
 Jack <venturajack85@...il.com>, Kent Overstreet
 <kent.overstreet@...ux.dev>, Gary Guo <gary@...yguo.net>,
 airlied@...il.com, boqun.feng@...il.com, david.laight.linux@...il.com,
 ej@...i.de, gregkh@...uxfoundation.org, hch@...radead.org, hpa@...or.com,
 ksummit@...ts.linux.dev, linux-kernel@...r.kernel.org,
 miguel.ojeda.sandonis@...il.com, rust-for-linux@...r.kernel.org
Subject: Re: C aggregate passing (Rust kernel policy)

On Wed, 26 Feb 2025 13:42:29 -0800
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, 26 Feb 2025 at 13:26, Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > As a bystander here, I just want to ask, do you mean basically to treat all
> > reads as READ_ONCE() and all writes as WRITE_ONCE()?  
> 
> Absolutely not.
> 
> I thought I made that clear:

Sorry, I didn't make myself clear. I shouldn't have said "all reads". What
I meant was the the "initial read".

Basically:

	r = READ_ONCE(*p);

and use what 'r' is from then on.

Where the compiler reads the source once and works with what it got.

To keep it from changing:

	r = *p;
	if (r > 1000)
		goto out;
	x = r;

to:

	if (*p > 1000)
		goto out;
	x = *p;

-- Steve