Re: [PATCH] shrink_dcache_parent() races against shrink_dcache_memory()

[Jan Blunck <jblunck@suse.de>]

On Sun, Jan 22, Andrew Morton wrote:

> > -void dput(struct dentry *dentry)
> > +static void dput_locked(struct dentry *dentry, struct list_head *list)
> >  {
> >  	if (!dentry)
> >  		return;
> >  
> > -repeat:
> > -	if (atomic_read(&dentry->d_count) == 1)
> > -		might_sleep();
> > -	if (!atomic_dec_and_lock(&dentry->d_count, &dcache_lock))
> > +	if (!atomic_dec_and_test(&dentry->d_count))
> >  		return;
> >  
> > +
> >
> > ...
> >
> > +void dput(struct dentry *dentry)
> > +{
> > +	LIST_HEAD(free_list);
> > +
> > +	if (!dentry)
> > +		return;
> > +
> > +	if (atomic_add_unless(&dentry->d_count, -1, 1))
> > +		return;
> > +
> > +	spin_lock(&dcache_lock);
> > +	dput_locked(dentry, &free_list);
> > +	spin_unlock(&dcache_lock);
> 
> This seems to be an open-coded copy of atomic_dec_and_lock()?
> 

Yes, it is. Otherwise the reference counting would be like

 if(!atomic_dec_and_lock())
	return;
 atomic_inc();
 dput_locked();

or something similar stupid/racy.

Regards,
	Jan

-- 
Jan Blunck                                               jblunck@suse.de
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