Re: rcu_read_lock lost its compiler barrier

From: Alan Stern
Date: Tue Jun 04 2019 - 13:04:02 EST

On Tue, 4 Jun 2019, Linus Torvalds wrote:

> So I don't technically disagree with anything you say,

That's good to know!

> I just wanted
> to point out that as far as the kernel is concerned, we do have higher
> quality expectations from the compiler than just "technically valid
> according to the C standard".

Which suggests asking whether these higher expectations should be
reflected in the Linux Kernel Memory Model. So far we have largely
avoided doing that sort of thing, although there are a few exceptions.

(For example, we assume the compiler does not destroy address
dependencies from volatile reads -- but we also warn that this
assumption may fail if the programmer does not follow some rules
described in one of Paul's documentation files.)