Re: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked()

[Andrea Parri]

On Tue, Apr 03, 2018 at 01:49:09PM +0100, David Howells wrote:
> Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > +/**
> > + * spin_is_locked() - Check whether a spinlock is locked.
> > + * @lock: Pointer to the spinlock.
> > + *
> > + * This function is NOT required to provide any memory ordering
> > + * guarantees; it could be used for debugging purposes or, when
> > + * additional synchronization is needed, accompanied with other
> > + * constructs (memory barriers) enforcing the synchronization.
> > + *
> > + * Return: 1, if @lock is (found to be) locked; 0, otherwise.
> 
> It's more complicated than that.  This function is dangerous and should be
> used with extreme care.  In the case where CONFIG_SMP=n the value is locked
> one way or the other and it might be the wrong way.

You mean "unlocked"? (aka, return 0)

  Andrea


> 
> David