Re: [RFC] possible badness in prune_dcache()

[Josef Bacik <jbacik@redhat.com>]

On Fri, Apr 04, 2008 at 02:44:08PM -0400, Josef Bacik wrote:
> On Fri, Apr 04, 2008 at 08:38:31PM +0200, Miklos Szeredi wrote:
> > > > probably worth looking at doing something different in the case of
> > > > shrinking the dcache on the parent, and leaving prune_dcache to
> > > > only be called in the case of trying to free up dcache under
> > > > memory pressure, where the superblock doesn't actually matter.
> > > > For the RHEL3 issue you are reffering to I fixed it by creating a
> > > > private list when we shrunk the parent, and submitting that list
> > > > to prune_dcache that way we didn't spend all this time looping.  I
> > > > will see what can be done for upstream.
> > 
> > Which sounds racy with umount.  A hashed dentry must either have a
> > refcount greater than one, or be on dentry_unused list.  This patch
> > breaks that assumption.
> >
> 
> It should be racy with umount, if we notice that we're being unmounted we just
> break, as the unmount will free the dentry's itself through another means.  I
> guess I could fix it so that prune_dcache will go through and add all the
> dentry's still on the dispose_list to the dentry_unused list at the end, but I
> don't see much of a reason for this since dentry_unused is just used to help
> keep track of what dentries can be flushed.
>

Hmm, thats shouldn't, not should.

Josef