Currently, we use bucket_lock when traversing bpf_sk_storage_map

elements. Since bpf_iter programs cannot use bpf_sk_storage_get() and bpf_sk_storage_delete() helpers which may also grab bucket lock, we do not have a deadlock issue which exists for hashmap when using bucket_lock ([1]). If a bucket contains a lot of sockets, during bpf_iter traversing a bucket, concurrent bpf_sk_storage_{get,delete}() may experience some undesirable delays. Using rcu_read_lock() is a reasonable compromise here. Although it may lose some precision, e.g., access stale sockets, but it will not hurt performance of other bpf programs. [1] https://lore.kernel.org/bpf/20200902235341.2001534-1-yhs@fb.com Cc: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Yonghong Song <yhs@fb.com> --- net/core/bpf_sk_storage.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-)

Author: yonghong-song

net/core/bpf_sk_storage.c

@@ -701,7 +701,7 @@ 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;
 }
@@ -715,7 +715,7 @@ bpf_sk_storage_map_seq_find_next(struct bpf_iter_seq_sk_storage_map_info *info,
 
 for (i = bucket_id; i < (1U << smap->bucket_log); i++) {
 b = &smap->buckets[i];
-raw_spin_lock_bh(&b->lock);
+rcu_read_lock();
 count = 0;
 hlist_for_each_entry(selem, &b->list, map_node) {
 sk_storage = rcu_dereference_raw(selem->local_storage);
@@ -726,7 +726,7 @@ bpf_sk_storage_map_seq_find_next(struct bpf_iter_seq_sk_storage_map_info *info,
 }
 count++;
 }
-raw_spin_unlock_bh(&b->lock);
+rcu_read_unlock();
 skip_elems = 0;
 }
 
@@ -806,13 +806,10 @@ static void bpf_sk_storage_map_seq_stop(struct seq_file *seq, void *v)
 struct bpf_local_storage_map *smap;
 struct bpf_local_storage_map_bucket *b;
 
-if (!v) {
+if (!v)
 (void)__bpf_sk_storage_map_seq_show(seq, v);
-} else {
-smap = (struct bpf_local_storage_map *)info->map;
-b = &smap->buckets[info->bucket_id];
-raw_spin_unlock_bh(&b->lock);
-}
+else
+rcu_read_unlock();
 }
 
 static int bpf_iter_init_sk_storage_map(void *priv_data,