Merge branch 'for-4.16/nfit' into libnvdimm-for-nextlibnvdimm-for-4.16

1 files changed, 9 insertions, 2 deletions

diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index 5ee2e41893d9..1712d319c2d8 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -591,8 +591,15 @@ static void sock_map_free(struct bpf_map *map)
 
 		write_lock_bh(&sock->sk_callback_lock);
 		psock = smap_psock_sk(sock);
-		smap_list_remove(psock, &stab->sock_map[i]);
-		smap_release_sock(psock, sock);
+		/* This check handles a racing sock event that can get the
+		 * sk_callback_lock before this case but after xchg happens
+		 * causing the refcnt to hit zero and sock user data (psock)
+		 * to be null and queued for garbage collection.
+		 */
+		if (likely(psock)) {
+			smap_list_remove(psock, &stab->sock_map[i]);
+			smap_release_sock(psock, sock);
+		}
 		write_unlock_bh(&sock->sk_callback_lock);
 	}
 	rcu_read_unlock();