Re: [RFC] possible badness in prune_dcache()

[Josef Bacik <jbacik@redhat.com>]

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.

Josef