On Wed, Sep 06, 2023 at 05:23:42PM +0200, Bernd Schubert wrote:
>
>
> On 9/6/23 17:20, Matthew Wilcox wrote:
> > On Thu, Aug 31, 2023 at 05:14:14PM +0200, Mateusz Guzik wrote:
> > > +++ b/include/linux/fs.h
> > > @@ -842,6 +842,16 @@ static inline void inode_lock_shared_nested(struct inode *inode, unsigned subcla
> > > down_read_nested(&inode->i_rwsem, subclass);
> > > }
> > > +static inline void inode_assert_locked(struct inode *inode)
> > > +{
> > > + lockdep_assert_held(&inode->i_rwsem);
> > > +}
> > > +
> > > +static inline void inode_assert_write_locked(struct inode *inode)
> > > +{
> > > + lockdep_assert_held_write(&inode->i_rwsem);
> > > +}
> >
> > This mirrors what we have in mm, but it's only going to trigger on
> > builds that have lockdep enabled. Lockdep is very expensive; it
> > easily doubles the time it takes to run xfstests on my laptop, so
> > I don't generally enable it. So what we also have in MM is:
> >
> > static inline void mmap_assert_write_locked(struct mm_struct *mm)
> > {
> > lockdep_assert_held_write(&mm->mmap_lock);
> > VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
> > }
> >
> > Now if you have lockdep enabled, you get the lockdep check which
> > gives you all the lovely lockdep information, but if you don't, you
> > at least get the cheap check that someone is holding the lock at all.
> >
> > ie I would make this:
> >
> > +static inline void inode_assert_write_locked(struct inode *inode)
> > +{
> > + lockdep_assert_held_write(&inode->i_rwsem);
> > + WARN_ON_ONCE(!inode_is_locked(inode));
> > +}
> >
> > Maybe the locking people could give us a rwsem_is_write_locked()
> > predicate, but until then, this is the best solution we came up with.
>
>
> Which is exactly what I had suggested in the other thread :)
Or hoist the XFS mrlock, because it actually /does/ know if the rwsem is
held in shared or exclusive mode.
--D
