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, Jun 28, 2026 at 01:34:22PM +0000, Yonatan Nachum wrote:
> On create AH, first check if the AH cache entry already exists and if
> so, returns the already stored AH number. If the entry doesn't exist,
> the driver creates it and calls the device to create the AH. A per-entry
> mutex serializes concurrent device commands on the same AH cache entry,
> ensuring only one thread issues the device create while others wait and
> reuse the result. If the device create fails, the entry's user count
> remains zero so subsequent threads will retry the device create.
> 
> On destroy AH, the user count is decremented under the entry mutex. If
> it reaches zero, the driver issues the device destroy command. After
> the device destroy completes, it removes the entry from the hashtable
> and frees it if no other references exist.  If new users arrived during
> the destroy, the entry remains in the hashtable for reuse.
> 
> Reviewed-by: Firas Jahjah <firasj@amazon.com>
> Reviewed-by: Michael Margolin <mrgolin@amazon.com>
> Signed-off-by: Yonatan Nachum <ynachum@amazon.com>
> ---
>  drivers/infiniband/hw/efa/efa_ah_cache.c | 94 ++++++++++++++++++++++++
>  drivers/infiniband/hw/efa/efa_ah_cache.h |  3 +
>  drivers/infiniband/hw/efa/efa_com_cmd.c  | 41 ++++++++++-
>  drivers/infiniband/hw/efa/efa_com_cmd.h  |  1 +
>  drivers/infiniband/hw/efa/efa_verbs.c    |  9 ++-
>  5 files changed, 140 insertions(+), 8 deletions(-)

<...>

> +/**
> + * 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