Re: [PATCH for-next v5 2/2] RDMA/efa: Add AH cache handling on create and destroy AH

[Leon Romanovsky <leon@kernel.org>]

On Sun, Jul 05, 2026 at 02:08:52PM +0000, Yonatan Nachum wrote:
> On Sun, Jul 05, 2026 at 04:35:06PM +0300, Leon Romanovsky wrote:
> > > +/**
> > > + * efa_ah_cache_put - Put a refcount of an AH cache entry
> > > + * @ah_cache: AH cache
> > > + * @entry: AH cache entry
> > > + *
> > > + * Drop the refcount. If it reaches zero, remove the entry from the hashtable
> > > + * and free it.
> > > + */
> > > +void efa_ah_cache_put(struct efa_ah_cache *ah_cache, struct efa_ah_cache_entry *entry)
> > > +{
> > > +	if (!refcount_dec_and_mutex_lock(&entry->refcount, &ah_cache->lock))
> > > +		return;
> > > +
> > > +	/* AH cache lock is held here */
> > > +	rhashtable_remove_fast(&ah_cache->hashtable, &entry->linkage, ah_cache_params);
> > > +	mutex_unlock(&ah_cache->lock);
> > > +
> > > +	mutex_destroy(&entry->lock);
> > > +	kfree_rcu(entry, rcu_head);
> > 
> > Where do you use RCU locking in this series? Why do you call
> > kfree_rcu() instead of kfree()?
> > 
> > Thanks
> 
> Originally I used kfree directly, but changed to kfree_rcu in v3
> following this Sashiko review and Jason's comment:
> https://sashiko.dev/#/patchset/20260512061121.2177521-1-ynachum%40amazon.com
> 
> If you think its not needed I can delete it.

I'm not sure you're using the right data structure for this task.

An RCU grace period is required to ensure that rhash has been unlinked
from ah_cache->hashtable, since a concurrent lookup may still succeed in
finding the deleted entry. The problem is that the refcount has already
been decremented to 0, and any attempt to increment it will trigger a
dmesg splat.

Thanks

> 
> Thanks