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

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Message-ID: <892324fc-9b75-4e8a-b3b6-cf3c5b4c3506@paulmck-laptop>
Date: Wed, 1 May 2024 12:02:29 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Marco Elver <elver@...gle.com>,
	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>
Subject: Re: [PATCH v3] tty: tty_io: remove hung_up_tty_fops

On Wed, May 01, 2024 at 11:56:26AM -0700, Linus Torvalds wrote:
> On Wed, 1 May 2024 at 11:46, Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > In short, I for one do greatly value KCSAN's help.  Along with that of
> > a great many other tools, none of which are perfect, but all of which
> > are helpful.
> 
> It's not that I don't value what KCSAN does, but I really think this
> is a KCSAN issue.
> 
> I absolutely *detest* these crazy "randomly add data race annotations".
> 
> Could we instead annotate particular structure fields? I don't want to
> mark things actually "volatile", because that then causes the compiler
> to generate absolutely horrendous code. But some KCSAN equivalent of
> "this field has data races, and we don't care" kind of annotation
> would be lovely..

That would give the poor sleep-deprived innocent bystander some way
to figure out which fields were shared, so that does sound like a good
improvement!

I would naively expect that KCSAN's ability to handle volatile fields
would make this doable, but there is much that I do not know about
KCSAN internals.  So I must defer to Marco on this one.

							Thanx, Paul