Re: [PATCH bpf-next v3] bpf: using rcu_read_lock for bpf_sk_storage_map iterator

[Yonghong Song]

On 9/16/20 10:55 AM, Martin KaFai Lau wrote:

On Tue, Sep 15, 2020 at 11:16:49PM -0700, Yonghong Song wrote:
[ ... ]

diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
index 4a86ea34f29e..d43c3d6d0693 100644
--- a/net/core/bpf_sk_storage.c
+++ b/net/core/bpf_sk_storage.c
@@ -678,6 +678,7 @@ struct bpf_iter_seq_sk_storage_map_info {
  static struct bpf_local_storage_elem *
  bpf_sk_storage_map_seq_find_next(struct bpf_iter_seq_sk_storage_map_info 
*info,
                                 struct bpf_local_storage_elem *prev_selem)
+       __acquires(RCU) __releases(RCU)
  {
        struct bpf_local_storage *sk_storage;
        struct bpf_local_storage_elem *selem;

In the while loop earlier in this function, if I read it correctly,
it is sort of continuing the earlier hlist_for_each_entry_rcu() for the
same bucket, so the hlist_entry_safe() needs to be changed also.
Something like this (uncompiled code):

         while (selem) {
-               selem = hlist_entry_safe(selem->map_node.next,
+               selem = 
hlist_entry_safe(rcu_dereference(hlist_next_rcu(&selem->map_node)),
                                          struct bpf_local_storage_elem, 
map_node);
                 if (!selem) {
                         /* not found, unlock and go to the next bucket */

Thanks and Ack. Will send v4 shortly.

@@ -701,11 +702,11 @@ bpf_sk_storage_map_seq_find_next(struct 
bpf_iter_seq_sk_storage_map_info *info,
                if (!selem) {
                        /* not found, unlock and go to the next bucket */
                        b = &smap->buckets[bucket_id++];
-                       raw_spin_unlock_bh(&b->lock);
+                       rcu_read_unlock();
                        skip_elems = 0;
                        break;
                }
-               sk_storage = rcu_dereference_raw(selem->local_storage);
+               sk_storage = rcu_dereference(selem->local_storage);
                if (sk_storage) {
                        info->skip_elems = skip_elems + count;
                        return selem;