Re: [PATCH 2/2] xen: privcmd: Add support for ioeventfd

[Juergen Gross]

On 09.10.23 12:53, Viresh Kumar wrote:
> On 09-10-23, 10:40, Alex Bennée wrote:
> > I thought generally sync points act as full barriers. Doing a bunch of
> > grepping I think ends at:
> >
> >    static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
> >    {
> >            unsigned long curr = (unsigned long)current;
> >
> >            return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
> >    }
> >
> > so you should already have completed your writes by that point.
>
> I am not sure if depending on such indirect mechanisms to implement
> barriers for you is a good idea.
>
> The situation here probably requires explicit barriers to make sure it
> doesn't break in future ?

Depending on lock implementations to include the needed barriers is fine IMO.

That is one central objective locks must ensure: to make sure any updates in
a locked region are operating on consistent data and being observable by
others after leaving the locked region.


Juergen

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