On Fri, Feb 2, 2018 at 6:30 AM, Paolo Abeni <pab...@redhat.com> wrote:
> The problem is that the htnode is freed before the linked knodes and the
> latter will try to access the first at u32_destroy_key() time.
> This change addresses the issue using the htnode refcnt to guarantee
> the correct free order. While at it also add a RCU annotation,
> to keep sparse happy.
>
> v1 -> v2: use rtnl_derefence() instead of RCU read locks
>
> Reported-by: Li Shuang <shu...@redhat.com>
> Fixes: c0d378ef1266 ("net_sched: use tcf_queue_work() in u32 filter")
> Signed-off-by: Paolo Abeni <pab...@redhat.com>
> ---
> net/sched/cls_u32.c | 19 +++++++++++++++----
> 1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> index 60c892c36a60..10440fbf3c68 100644
> --- a/net/sched/cls_u32.c
> +++ b/net/sched/cls_u32.c
> @@ -398,10 +398,12 @@ static int u32_init(struct tcf_proto *tp)
> static int u32_destroy_key(struct tcf_proto *tp, struct tc_u_knode *n,
> bool free_pf)
> {
> + struct tc_u_hnode *ht = rtnl_dereference(n->ht_down);
> +
> tcf_exts_destroy(&n->exts);
> tcf_exts_put_net(&n->exts);
> - if (n->ht_down)
> - n->ht_down->refcnt--;
> + if (ht && ht->refcnt-- == 0)
> + kfree(ht);
> #ifdef CONFIG_CLS_U32_PERF
> if (free_pf)
> free_percpu(n->pf);
> @@ -624,7 +626,12 @@ static int u32_destroy_hnode(struct tcf_proto *tp,
> struct tc_u_hnode *ht,
> idr_destroy(&ht->handle_idr);
> idr_remove_ext(&tp_c->handle_idr, ht->handle);
> RCU_INIT_POINTER(*hn, ht->next);
> - kfree_rcu(ht, rcu);
> +
> + /* u32_destroy_key() will will later free ht for us,
> if
> + * it's still referenced by some knode
> + */
> + if (ht->refcnt == 0)
> + kfree_rcu(ht, rcu);
Isn't u32_destroy_hnode() always called with ht->refcnt==0 ?
So no need this check at all?
> return 0;
> }
> }
> @@ -667,7 +674,11 @@ static void u32_destroy(struct tcf_proto *tp, struct
> netlink_ext_ack *extack)
>
> while ((ht = rtnl_dereference(tp_c->hlist)) != NULL) {
> RCU_INIT_POINTER(tp_c->hlist, ht->next);
> - kfree_rcu(ht, rcu);
> + /* u32_destroy_key() will will later free ht for us,
> if
Nit: double "will"
> + * it's still referenced by some knode
> + */
> + if (ht->refcnt == 0)
> + kfree_rcu(ht, rcu);
This part looks fine.
Thanks!
