Re: [PATCHv3 0/2]

Keith Busch
2025-02-28T14:58:27Z

On Fri, Feb 28, 2025 at 06:32:47AM -0800, Sean Christopherson wrote:
> On Fri, Feb 28, 2025, Sean Christopherson wrote:
> > On Fri, Feb 28, 2025, Lei Yang wrote:
> > > Hi Keith
> > >
> > > V3 introduced a new bug, the following error messages from qemu output
> > > after applying this patch to boot up a guest.
> >
> > Doh, my bug. Not yet tested, but this should fix things. Assuming it does, I'll
> > post a v3 so I can add my SoB.
> v4
>
> Confirmed that it worked, but deleting the pre-mutex check for ONCE_COMPLETED.
> Will post v4 later today.
>
> > diff --git a/include/linux/call_once.h b/include/linux/call_once.h
> > index ddcfd91493ea..b053f4701c94 100644
> > --- a/include/linux/call_once.h
> > +++ b/include/linux/call_once.h
> > @@ -35,10 +35,12 @@ static inline int call_once(struct once *once, int (*cb)(struct once *))
> > return 0;
> >
> > guard(mutex)(&once->lock);
> > - WARN_ON(atomic_read(&once->state) == ONCE_RUNNING);
> > - if (atomic_read(&once->state) != ONCE_NOT_STARTED)
> > + if (WARN_ON(atomic_read(&once->state) == ONCE_RUNNING))
> > return -EINVAL;
> >
> > + if (atomic_read(&once->state) == ONCE_COMPLETED)
> > + return 0;
> > +
> > atomic_set(&once->state, ONCE_RUNNING);
> > r = cb(once);
> > if (r)

Possible suggestion since it seems odd to do an atomic_read twice on the
same value. Maybe make this a switch:

switch (atomic_read(&once->state) {
case ONCE_NOT_STARTED:
atomic_set(&once->state, ONCE_RUNNING);
break;
case ONCE_COMPLETED:
return 0;
case ONCE_RUNNING:
default:
WARN_ON(1);
return -EINVAL;
}