On Wed, Sep 06, 2023 at 07:33:48PM +0100, Matthew Wilcox wrote:
> On Wed, Sep 06, 2023 at 10:07:24AM -0700, Darrick J. Wong wrote:
> > On Wed, Sep 06, 2023 at 05:00:14PM +0100, Matthew Wilcox wrote:
> > > +++ b/fs/xfs/xfs_inode.c
> > > @@ -361,7 +361,7 @@ xfs_isilocked(
> > > {
> > > if (lock_flags & (XFS_ILOCK_EXCL|XFS_ILOCK_SHARED)) {
> > > if (!(lock_flags & XFS_ILOCK_SHARED))
> > > - return !!ip->i_lock.mr_writer;
> > > + return rwsem_is_write_locked(&ip->i_lock.mr_lock);
> >
> > You'd be better off converting this to:
> >
> > return __xfs_rwsem_islocked(&ip->i_lock.mr_lock,
> > (lock_flags & XFS_ILOCK_SHARED));
> >
> > And then fixing __xfs_rwsem_islocked to do:
> >
> > static inline bool
> > __xfs_rwsem_islocked(
> > struct rw_semaphore *rwsem,
> > bool shared)
> > {
> > if (!debug_locks) {
> > if (!shared)
> > return rwsem_is_write_locked(rwsem);
> > return rwsem_is_locked(rwsem);
> > }
> >
> > ...
> > }
>
> Thanks.
>
> > > +++ b/include/linux/rwsem.h
> > > @@ -72,6 +72,11 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
> > > return atomic_long_read(&sem->count) != 0;
> > > }
> > >
> > > +static inline int rwsem_is_write_locked(struct rw_semaphore *sem)
> > > +{
> > > + return atomic_long_read(&sem->count) & 1;
> >
> >
> > atomic_long_read(&sem->count) & RWSEM_WRITER_LOCKED ?
>
> Then this would either have to be in rwsem.c or we'd have to move the
> definition of RWSEM_WRITER_LOCKED to rwsem.h. All three options are
> kind of bad. I think I hate the bare '1' least.
I disagree, because using the bare 1 brings the most risk that someone
will subtly break the locking assertions some day when they get the
bright idea to move RWSEM_WRITER_LOCKED to the upper bit and fail to
notice this predicate and its magic number. IMO moving it to the header
file (possibly with the usual __ prefix) would be preferable to leaving
a landmine.
--D
