On Wed, Jun 12, 2024 at 03:37:55PM -0700, Paul E. McKenney wrote:

quoted

On Wed, Jun 12, 2024 at 02:33:05PM -0700, Jakub Kicinski wrote:

quoted

On Sun,  9 Jun 2024 10:27:12 +0200 Julia Lawall wrote:

quoted

Since SLOB was removed, it is not necessary to use call_rcu
when the callback only performs kmem_cache_free. Use
kfree_rcu() directly.

The changes were done using the following Coccinelle semantic patch.
This semantic patch is designed to ignore cases where the callback
function is used in another way.

How does the discussion on:
  [PATCH] Revert "batman-adv: prefer kfree_rcu() over call_rcu() with free-only callbacks"
  https://lore.kernel.org/all/20240612133357.2596-1-linus.luessing@c0d3.blue/ (local)
reflect on this series? IIUC we should hold off..

We do need to hold off for the ones in kernel modules (such as 07/14)
where the kmem_cache is destroyed during module unload.

OK, I might as well go through them...

[PATCH 01/14] wireguard: allowedips: replace call_rcu by kfree_rcu for simple kmem_cache_free callback
	Needs to wait, see wg_allowedips_slab_uninit().

Also, notably, this patch needs additionally:

diff --git a/drivers/net/wireguard/allowedips.c b/drivers/net/wireguard/allowedips.c
index e4e1638fce1b..c95f6937c3f1 100644
--- a/drivers/net/wireguard/allowedips.c
+++ b/drivers/net/wireguard/allowedips.c

@@ -377,7 +377,6 @@ int __init wg_allowedips_slab_init(void)

 void wg_allowedips_slab_uninit(void)
 {
-	rcu_barrier();
 	kmem_cache_destroy(node_cache);
 }

Once kmem_cache_destroy has been fixed to be deferrable.

I assume the other patches are similar -- an rcu_barrier() can be
removed. So some manual meddling of these might be in order.