linux-kernel - Re: [PATCH v3] tty: tty_io: remove hung_up_tty

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Message-ID: <CAHk-=whnQXNVwuf42Sh2ngBGhBqbJjUfq5ux6e7Si_XSPAt05A@mail.gmail.com>
Date: Mon, 29 Apr 2024 08:38:28 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Marco Elver <elver@...gle.com>
Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Dmitry Vyukov <dvyukov@...gle.com>, 
	syzbot <syzbot+b7c3ba8cdc2f6cf83c21@...kaller.appspotmail.com>, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	Nathan Chancellor <nathan@...nel.org>, Arnd Bergmann <arnd@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, 
	Jiri Slaby <jirislaby@...nel.org>, "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v3] tty: tty_io: remove hung_up_tty_fops

On Mon, 29 Apr 2024 at 06:56, Marco Elver <elver@...gle.com> wrote:
>
> A WRITE_ONCE() / READ_ONCE() pair would do it here. What should we use instead?

Why would we annotate a "any other code generation is insane" issues at all?

When we do chained pointer loads in

    file->f_op->op()

and we say "I don't care what value I get for the middle one", I don't
see the value in annotating that at all.

There is no compiler that will sanely and validly do a pointer chain
load by *anything* but a load. And it doesn't matter to us if it then
spills and reloads, it will *STILL* be a load.

We're not talking about "extract different bits in separate
operations". We're talking about following one pointer that can point
to two separate static values.

Reality matters. A *lot* more than some "C standard" that we already
have ignored for decades because it's not strong enough.

                       Linus