Re: [PATCH v4 1/1] NFSD: Enforce Timeout on Layout Recall and Integrate Lease Manager Fencing

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2026-01-27 at 12:11 -0500, Chuck Lever wrote:
> 
> > +
> > +	if (work_busy(&ls->ls_fence_work.work))
> > +		return false;
> > +	/* Schedule work to do the fence operation */
> > +	ret = mod_delayed_work(system_dfl_wq, &ls->ls_fence_work, 0);
> > +	if (!ret) {
> > +		/*
> > +		 * If there is no pending work, mod_delayed_work queues
> > +		 * new task. While fencing is in progress, a reference
> > +		 * count is added to the layout stateid to ensure its
> > +		 * validity. This reference count is released once fencing
> > +		 * has been completed.
> > +		 */
> > +		refcount_inc(&ls->ls_stid.sc_count);
> > +		++ls->ls_fence_retry_cnt;
> > +		return true;
> > +	}
> 
> Incrementing after the mod_delayed_work() call is racy. Instead:
> 
> refcount_inc(&ls->ls_stid.sc_count);
> ret = mod_delayed_work(system_dfl_wq, &ls->ls_fence_work, 0);
> if (ret) {
>     refcount_dec(&ls->ls_stid.sc_count);
>     ....
> }
> 

Is that safe? That's done in nfsd_break_one_deleg() for similar
reasons, but there is a comment over that function explaining why it's
OK.

We'll need to validate that the lease is always released before the
sc_count goes to 0 here too. At first glance, it doesn't look like that
is the case.


-- 
Jeff Layton <jlayton@kernel.org>