Re: [PATCH v5 1/4] xfs: Refactor xfs_isilocked()

[Christoph Hellwig <hch@infradead.org>]

On Tue, Feb 18, 2020 at 08:48:21PM -0800, Darrick J. Wong wrote:
> > > +static inline bool
> > > +__xfs_rwsem_islocked(
> > > +	struct rw_semaphore	*rwsem,
> > > +	bool			shared,
> > > +	bool			excl)
> > > +{
> > > +	bool locked = false;
> > > +
> > > +	if (!rwsem_is_locked(rwsem))
> > > +		return false;
> > > +
> > > +	if (!debug_locks)
> > > +		return true;
> > > +
> > > +	if (shared)
> > > +		locked = lockdep_is_held_type(rwsem, 0);
> > > +
> > > +	if (excl)
> > > +		locked |= lockdep_is_held_type(rwsem, 1);
> > > +
> > > +	return locked;
> > 
> > This could use some comments explaining the logic, especially why we
> > need the shared and excl flags, which seems very confusing given that
> > a lock can be held either shared or exclusive, but not neither and not
> > both.
> 
> Yes, this predicate should document that callers are allowed to pass in
> shared==true and excl==true when the caller wants to assert that either
> lock type (shared or excl) of a given lock class (e.g. iolock) are held.

Looking at the lockdep_is_held_type implementation, and our existing
code for i_rwsem I really don't see the point of the extra shared
check.  Something like:

static inline bool
__xfs_rwsem_islocked(
	struct rw_semaphore	*rwsem,
	bool			excl)
{
	if (rwsem_is_locked(rwsem)) {
		if (debug_locks && excl)
			return lockdep_is_held_type(rwsem, 1);
		return true;
	}

	return false;
}

should be all that we really need.