Re: [PATCH v2] locks: skip posix unlock when there are no posix locks

[David Teigland <teigland@redhat.com>]

On Fri, Aug 19, 2011 at 01:09:36PM -0400, Trond Myklebust wrote:
> >  void locks_remove_posix(struct file *filp, fl_owner_t owner)
> >  {
> >  	struct file_lock lock;
> > +	struct file_lock **before;
> > +	struct inode *inode;
> >  
> >  	/*
> >  	 * If there are no locks held on this file, we don't need to call
> >  	 * posix_lock_file().  Another process could be setting a lock on this
> >  	 * file at the same time, but we wouldn't remove that lock anyway.
> >  	 */
> > -	if (!filp->f_path.dentry->d_inode->i_flock)
> > +	inode = filp->f_path.dentry->d_inode;
> > +
> > +	if (!inode->i_flock)
> >  		return;
> >  
> > +	lock_flocks();
> > +	for_each_lock(inode, before) {
> > +		struct file_lock *fl = *before;
> > +		if (IS_POSIX(fl))
> > +			goto do_unlock;
> > +	}
> > +	unlock_flocks();
> > +	return;
> > +
> > +do_unlock:
> > +	unlock_flocks();
> >  	lock.fl_type = F_UNLCK;
> >  	lock.fl_flags = FL_POSIX | FL_CLOSE;
> >  	lock.fl_start = 0;
> 
> This assumes that all locks are mirrored in inode->i_flock, which may
> not be the case if the filesystem implements its own f_op->lock(). The
> right place for this optimisation would be in your filesystem callback.

I suppose if i_flock is being faked at the same time to avoid the null
check.  I once looked at not doing lock mirroring in vfs and couldn't for
reasons I don't remember... may the null i_flock check was the only
reason, not sure.

Dave