Jesper Dangaard Brouer wrote:
Adjusting SLAB_DESTROY_BY_RCU flags.
kmem_cache_create("nf_conntrack", ...) does not need the
SLAB_DESTROY_BY_RCU flag.
It does need it. We're using it instead of call_rcu() for conntracks.
But the
kmem_cache_create("nf_conntrack_expect", ...) should use the
SLAB_DESTROY_BY_RCU flag, because it uses a call_rcu() callback to
invoke kmem_cache_free().
No, using call_rcu() means we don't need SLAB_DESTROY_BY_RCU.
Please see the note in include/linux/slab.h.
RCU barriers, rcu_barrier(), is inserted two places.
In nf_conntrack_expect.c nf_conntrack_expect_fini() before the
kmem_cache_destroy(), even though the use of the SLAB_DESTROY_BY_RCU
flag, because slub does not (currently) handle rcu sync correctly.
I think that should be fixed in slub then.
And in nf_conntrack_extend.c nf_ct_extend_unregister(), inorder to
wait for completion of callbacks to __nf_ct_ext_free_rcu(), which is
invoked by __nf_ct_ext_add(). It might be more efficient to call
rcu_barrier() in nf_conntrack_core.c nf_conntrack_cleanup_net(), but
thats make it more difficult to read the code (as the callback code
in located in nf_conntrack_extend.c).
This one looks fine.
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 5f72b94..438ce84 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1242,7 +1242,7 @@ static int nf_conntrack_init_init_net(void)
nf_conntrack_cachep = kmem_cache_create("nf_conntrack",
sizeof(struct nf_conn),
- 0, SLAB_DESTROY_BY_RCU, NULL);
+ 0, 0, NULL);
if (!nf_conntrack_cachep) {
printk(KERN_ERR "Unable to create nf_conn slab cache\n");
ret = -ENOMEM;
diff --git a/net/netfilter/nf_conntrack_expect.c b/net/netfilter/nf_conntrack_expect.c
index afde8f9..56227c2 100644
--- a/net/netfilter/nf_conntrack_expect.c
+++ b/net/netfilter/nf_conntrack_expect.c
@@ -593,7 +593,7 @@ int nf_conntrack_expect_init(struct net *net)
if (net_eq(net, &init_net)) {
nf_ct_expect_cachep = kmem_cache_create("nf_conntrack_expect",
sizeof(struct nf_conntrack_expect),
- 0, 0, NULL);
+ 0, SLAB_DESTROY_BY_RCU, NULL);
if (!nf_ct_expect_cachep)
goto err2;
}
@@ -617,8 +617,15 @@ err1:
void nf_conntrack_expect_fini(struct net *net)
{
exp_proc_remove(net);
- if (net_eq(net, &init_net))
+ if (net_eq(net, &init_net)) {
+ /* hawk@xxxxxxx 2009-06-24: The rcu_barrier() can be
+ * removed once the sl*b allocators has been fixed
+ * regarding handling the SLAB_DESTROY_BY_RCU flag
+ * correctly.
+ */
+ rcu_barrier(); /* Wait for call_rcu() before destroy */
kmem_cache_destroy(nf_ct_expect_cachep);
+ }
nf_ct_free_hashtable(net->ct.expect_hash, net->ct.expect_vmalloc,
nf_ct_expect_hsize);
}
diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c
index 4b2c769..fef95be 100644
--- a/net/netfilter/nf_conntrack_extend.c
+++ b/net/netfilter/nf_conntrack_extend.c
@@ -186,6 +186,6 @@ void nf_ct_extend_unregister(struct nf_ct_ext_type *type)
rcu_assign_pointer(nf_ct_ext_types[type->id], NULL);
update_alloc_size(type);
mutex_unlock(&nf_ct_ext_type_mutex);
- synchronize_rcu();
+ rcu_barrier(); /* Wait for completion of call_rcu()'s */
}
EXPORT_SYMBOL_GPL(nf_ct_extend_unregister);
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