net: sched: rcu'ify cls_bpf

This patch makes the cls_bpf classifier RCU safe. The tcf_lock
was being used to protect a list of cls_bpf_prog now this list
is RCU safe and updates occur with rcu_replace.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index 0e30d58..6a7386e 100644 (file)
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -27,6 +27,7 @@ MODULE_DESCRIPTION("TC BPF based classifier");
 struct cls_bpf_head {
        struct list_head plist;
        u32 hgen;
+       struct rcu_head rcu;
 };
 
 struct cls_bpf_prog {
@@ -37,6 +38,8 @@ struct cls_bpf_prog {
        struct list_head link;
        u32 handle;
        u16 bpf_len;
+       struct tcf_proto *tp;
+       struct rcu_head rcu;
 };
 
 static const struct nla_policy bpf_policy[TCA_BPF_MAX + 1] = {
@@ -49,11 +52,11 @@ static const struct nla_policy bpf_policy[TCA_BPF_MAX + 1] = {
 static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
                            struct tcf_result *res)
 {
-       struct cls_bpf_head *head = tp->root;
+       struct cls_bpf_head *head = rcu_dereference(tp->root);
        struct cls_bpf_prog *prog;
        int ret;
 
-       list_for_each_entry(prog, &head->plist, link) {
+       list_for_each_entry_rcu(prog, &head->plist, link) {
                int filter_res = BPF_PROG_RUN(prog->filter, skb);
 
                if (filter_res == 0)
@@ -81,8 +84,8 @@ static int cls_bpf_init(struct tcf_proto *tp)
        if (head == NULL)
                return -ENOBUFS;
 
-       INIT_LIST_HEAD(&head->plist);
-       tp->root = head;
+       INIT_LIST_HEAD_RCU(&head->plist);
+       rcu_assign_pointer(tp->root, head);
 
        return 0;
 }
@@ -98,18 +101,22 @@ static void cls_bpf_delete_prog(struct tcf_proto *tp, struct cls_bpf_prog *prog)
        kfree(prog);
 }
 
+static void __cls_bpf_delete_prog(struct rcu_head *rcu)
+{
+       struct cls_bpf_prog *prog = container_of(rcu, struct cls_bpf_prog, rcu);
+
+       cls_bpf_delete_prog(prog->tp, prog);
+}
+
 static int cls_bpf_delete(struct tcf_proto *tp, unsigned long arg)
 {
-       struct cls_bpf_head *head = tp->root;
+       struct cls_bpf_head *head = rtnl_dereference(tp->root);
        struct cls_bpf_prog *prog, *todel = (struct cls_bpf_prog *) arg;
 
        list_for_each_entry(prog, &head->plist, link) {
                if (prog == todel) {
-                       tcf_tree_lock(tp);
-                       list_del(&prog->link);
-                       tcf_tree_unlock(tp);
-
-                       cls_bpf_delete_prog(tp, prog);
+                       list_del_rcu(&prog->link);
+                       call_rcu(&prog->rcu, __cls_bpf_delete_prog);
                        return 0;
                }
        }
@@ -119,27 +126,28 @@ static int cls_bpf_delete(struct tcf_proto *tp, unsigned long arg)
 
 static void cls_bpf_destroy(struct tcf_proto *tp)
 {
-       struct cls_bpf_head *head = tp->root;
+       struct cls_bpf_head *head = rtnl_dereference(tp->root);
        struct cls_bpf_prog *prog, *tmp;
 
        list_for_each_entry_safe(prog, tmp, &head->plist, link) {
-               list_del(&prog->link);
-               cls_bpf_delete_prog(tp, prog);
+               list_del_rcu(&prog->link);
+               call_rcu(&prog->rcu, __cls_bpf_delete_prog);
        }
 
-       kfree(head);
+       RCU_INIT_POINTER(tp->root, NULL);
+       kfree_rcu(head, rcu);
 }
 
 static unsigned long cls_bpf_get(struct tcf_proto *tp, u32 handle)
 {
-       struct cls_bpf_head *head = tp->root;
+       struct cls_bpf_head *head = rtnl_dereference(tp->root);
        struct cls_bpf_prog *prog;
        unsigned long ret = 0UL;
 
        if (head == NULL)
                return 0UL;
 
-       list_for_each_entry(prog, &head->plist, link) {
+       list_for_each_entry_rcu(prog, &head->plist, link) {
                if (prog->handle == handle) {
                        ret = (unsigned long) prog;
                        break;
@@ -158,10 +166,10 @@ static int cls_bpf_modify_existing(struct net *net, struct tcf_proto *tp,
                                   unsigned long base, struct nlattr **tb,
                                   struct nlattr *est, bool ovr)
 {
-       struct sock_filter *bpf_ops, *bpf_old;
+       struct sock_filter *bpf_ops;
        struct tcf_exts exts;
        struct sock_fprog_kern tmp;
-       struct bpf_prog *fp, *fp_old;
+       struct bpf_prog *fp;
        u16 bpf_size, bpf_len;
        u32 classid;
        int ret;
@@ -197,26 +205,15 @@ static int cls_bpf_modify_existing(struct net *net, struct tcf_proto *tp,
        if (ret)
                goto errout_free;
 
-       tcf_tree_lock(tp);
-       fp_old = prog->filter;
-       bpf_old = prog->bpf_ops;
-
        prog->bpf_len = bpf_len;
        prog->bpf_ops = bpf_ops;
        prog->filter = fp;
        prog->res.classid = classid;
-       tcf_tree_unlock(tp);
 
        tcf_bind_filter(tp, &prog->res, base);
        tcf_exts_change(tp, &prog->exts, &exts);
 
-       if (fp_old)
-               bpf_prog_destroy(fp_old);
-       if (bpf_old)
-               kfree(bpf_old);
-
        return 0;
-
 errout_free:
        kfree(bpf_ops);
 errout:
@@ -244,9 +241,10 @@ static int cls_bpf_change(struct net *net, struct sk_buff *in_skb,
                          u32 handle, struct nlattr **tca,
                          unsigned long *arg, bool ovr)
 {
-       struct cls_bpf_head *head = tp->root;
-       struct cls_bpf_prog *prog = (struct cls_bpf_prog *) *arg;
+       struct cls_bpf_head *head = rtnl_dereference(tp->root);
+       struct cls_bpf_prog *oldprog = (struct cls_bpf_prog *) *arg;
        struct nlattr *tb[TCA_BPF_MAX + 1];
+       struct cls_bpf_prog *prog;
        int ret;
 
        if (tca[TCA_OPTIONS] == NULL)
@@ -256,18 +254,19 @@ static int cls_bpf_change(struct net *net, struct sk_buff *in_skb,
        if (ret < 0)
                return ret;
 
-       if (prog != NULL) {
-               if (handle && prog->handle != handle)
-                       return -EINVAL;
-               return cls_bpf_modify_existing(net, tp, prog, base, tb,
-                                              tca[TCA_RATE], ovr);
-       }
-
        prog = kzalloc(sizeof(*prog), GFP_KERNEL);
-       if (prog == NULL)
+       if (!prog)
                return -ENOBUFS;
 
        tcf_exts_init(&prog->exts, TCA_BPF_ACT, TCA_BPF_POLICE);
+
+       if (oldprog) {
+               if (handle && oldprog->handle != handle) {
+                       ret = -EINVAL;
+                       goto errout;
+               }
+       }
+
        if (handle == 0)
                prog->handle = cls_bpf_grab_new_handle(tp, head);
        else
@@ -281,16 +280,17 @@ static int cls_bpf_change(struct net *net, struct sk_buff *in_skb,
        if (ret < 0)
                goto errout;
 
-       tcf_tree_lock(tp);
-       list_add(&prog->link, &head->plist);
-       tcf_tree_unlock(tp);
+       if (oldprog) {
+               list_replace_rcu(&prog->link, &oldprog->link);
+               call_rcu(&oldprog->rcu, __cls_bpf_delete_prog);
+       } else {
+               list_add_rcu(&prog->link, &head->plist);
+       }
 
        *arg = (unsigned long) prog;
-
        return 0;
 errout:
-       if (*arg == 0UL && prog)
-               kfree(prog);
+       kfree(prog);
 
        return ret;
 }
@@ -339,10 +339,10 @@ nla_put_failure:
 
 static void cls_bpf_walk(struct tcf_proto *tp, struct tcf_walker *arg)
 {
-       struct cls_bpf_head *head = tp->root;
+       struct cls_bpf_head *head = rtnl_dereference(tp->root);
        struct cls_bpf_prog *prog;
 
-       list_for_each_entry(prog, &head->plist, link) {
+       list_for_each_entry_rcu(prog, &head->plist, link) {
                if (arg->count < arg->skip)
                        goto skip;
                if (arg->fn(tp, (unsigned long) prog, arg) < 0) {