On Wed, Jun 12, 2024 at 02:33:05PM -0700, Jakub Kicinski wrote: > On Sun, 9 Jun 2024 10:27:12 +0200 Julia Lawall wrote: > > 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@xxxxxxxxx/ > 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(). [PATCH 02/14] net: replace call_rcu by kfree_rcu for simple kmem_cache_free callback I don't immediately see the rcu_barrier(), but if there isn't one in there somewhere there probably should be. Caution suggests a need to wait. [PATCH 03/14] KVM: PPC: replace call_rcu by kfree_rcu for simple kmem_cache_free callback I don't immediately see the rcu_barrier(), but if there isn't one in there somewhere there probably should be. Caution suggests a need to wait. [PATCH 04/14] xfrm6_tunnel: replace call_rcu by kfree_rcu for simple kmem_cache_free callback Needs to wait, see xfrm6_tunnel_fini(). [PATCH 05/14] tracefs: replace call_rcu by kfree_rcu for simple kmem_cache_free callback This one is fine because the tracefs_inode_cachep kmem_cache is created at boot and never destroyed. [PATCH 06/14] eCryptfs: replace call_rcu by kfree_rcu for simple kmem_cache_free callback I don't see a kmem_cache_destroy(), but then again, I also don't see the kmem_cache_create(). Unless someone can see what I am not seeing, let's wait. [PATCH 07/14] net: bridge: replace call_rcu by kfree_rcu for simple kmem_cache_free callback Needs to wait, see br_fdb_fini() and br_deinit(). [PATCH 08/14] nfsd: replace call_rcu by kfree_rcu for simple kmem_cache_free callback I don't immediately see the rcu_barrier(), but if there isn't one in there somewhere there probably should be. Caution suggests a need to wait. [PATCH 09/14] block: replace call_rcu by kfree_rcu for simple kmem_cache_free callback I don't see a kmem_cache_destroy(), but then again, I also don't see the kmem_cache_create(). Unless someone can see what I am not seeing, let's wait. [PATCH 10/14] can: gw: replace call_rcu by kfree_rcu for simple kmem_cache_free callback Needs to wait, see cgw_module_exit(). [PATCH 11/14] posix-timers: replace call_rcu by kfree_rcu for simple kmem_cache_free callback This one is fine because the posix_timers_cache kmem_cache is created at boot and never destroyed. [PATCH 12/14] workqueue: replace call_rcu by kfree_rcu for simple kmem_cache_free callback This one is fine because the pwq_cache kmem_cache is created at boot and never destroyed. [PATCH 13/14] kcm: replace call_rcu by kfree_rcu for simple kmem_cache_free callback I don't immediately see the rcu_barrier(), but if there isn't one in there somewhere there probably should be. Caution suggests a need to wait. [PATCH 14/14] netfilter: replace call_rcu by kfree_rcu for simple kmem_cache_free callback Needs to wait, see hashlimit_mt_exit(). So 05/14, 11/14 and 12/14 are OK and can go ahead. The rest need some help. Apologies for my having gotten overly enthusiastic about this change! Thanx, Paul
