Re: [GIT PULL] pipe: nonblocking rw for io_uring

[Linus Torvalds]

On Tue, Apr 25, 2023 at 12:49 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> The last time this came up I shared your view however Mark argued for
> the READ_ONCE() thusly:
>
>   https://lore.kernel.org/all/Y71LoCIl+IFdy9D8@FVFF77S0Q05N/T/#u

Hmm.

Yes, I think Mark is right. It's not that 'old' might be wrong - that
doesn't matter because cmpxchg will work it out - it's just that 'new'
might not be consistent with the old value we then use.

Ok. I'll try to remember this, but maybe it might be worth documenting.

Jens - I don't think this actually matters for the f_mode value issue,
since the only thing that might change is that FMODE_NOWAIT bit, but I
was clearly wrong on READ_ONCE(). So that loop should have it, just to
have the right pattern after all.

My bad.

             Linus