Re: [PATCH 1/3] locking/ww_mutex: cleanup lock->ctx usage in amdgpu

[Christian KÃnig]

Am 20.02.2018 um 13:35 schrieb Peter Zijlstra:
> This really should've been Cc'ed to me.
>
> On Thu, Feb 15, 2018 at 03:19:42PM +0100, Christian KÃnig wrote:
> > diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
> > index 39fda195bf78..dd580db289e8 100644
> > --- a/include/linux/ww_mutex.h
> > +++ b/include/linux/ww_mutex.h
> > @@ -358,4 +358,21 @@ static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
> >   	return mutex_is_locked(&lock->base);
> >   }
> >   
> > +/**
> > + * ww_mutex_is_owned_by - is the w/w mutex locked by this task in that context
> > + * @lock: the mutex to be queried
> > + * @task: the task structure to check
> > + * @ctx: the w/w acquire context to test
> > + *
> > + * Returns true if the mutex is locked in the context by the given task, false
> > + * otherwise.
> > + */
> > +static inline bool ww_mutex_is_owned_by(struct ww_mutex *lock,
> > +					struct task_struct *task,
> > +					struct ww_acquire_ctx *ctx)
> > +{
> > +	return likely(__mutex_owner(&lock->base) == task) &&
> > +		READ_ONCE(lock->ctx) == ctx;
> > +}
> Nak on that interface, that's racy and broken by design.

Why?

Regards,
Christian.