Re: [PATCH v3] tty: tty_io: remove hung_up_tty_fops

[Marco Elver]

On Wed, 1 May 2024 at 21:02, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx> 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.

This is relatively trivial:

#ifdef __SANITIZE_THREAD__
#define __data_racy volatile
#endif

KCSAN will just ignore racy access to them (it will pretend they are "marked").

In some cases it might cause the compiler to complain if converting a
volatile pointer to a non-volatile pointer, but I suspect that the
corresponding pointer should then similarly be marked as __data_racy.
The fact that without casting the attribute is "viral" is probably WAI
even in this case.

Do we want this kind of attribute?

Thanks,
-- Marco