1 files changed, 27 insertions, 7 deletions

diff --git a/net/ipv4/tcp_memcontrol.c b/net/ipv4/tcp_memcontrol.c
index 151703791bb0..b6f3583ddfe8 100644
--- a/net/ipv4/tcp_memcontrol.c
+++ b/net/ipv4/tcp_memcontrol.c
@@ -74,9 +74,6 @@ void tcp_destroy_cgroup(struct mem_cgroup *memcg)
 	percpu_counter_destroy(&tcp->tcp_sockets_allocated);
 
 	val = res_counter_read_u64(&tcp->tcp_memory_allocated, RES_LIMIT);
-
-	if (val != RESOURCE_MAX)
-		static_key_slow_dec(&memcg_socket_limit_enabled);
 }
 EXPORT_SYMBOL(tcp_destroy_cgroup);
 
@@ -107,10 +104,33 @@ static int tcp_update_limit(struct mem_cgroup *memcg, u64 val)
 		tcp->tcp_prot_mem[i] = min_t(long, val >> PAGE_SHIFT,
 					     net->ipv4.sysctl_tcp_mem[i]);
 
-	if (val == RESOURCE_MAX && old_lim != RESOURCE_MAX)
-		static_key_slow_dec(&memcg_socket_limit_enabled);
-	else if (old_lim == RESOURCE_MAX && val != RESOURCE_MAX)
-		static_key_slow_inc(&memcg_socket_limit_enabled);
+	if (val == RESOURCE_MAX)
+		clear_bit(MEMCG_SOCK_ACTIVE, &cg_proto->flags);
+	else if (val != RESOURCE_MAX) {
+		/*
+		 * The active bit needs to be written after the static_key
+		 * update. This is what guarantees that the socket activation
+		 * function is the last one to run. See sock_update_memcg() for
+		 * details, and note that we don't mark any socket as belonging
+		 * to this memcg until that flag is up.
+		 *
+		 * We need to do this, because static_keys will span multiple
+		 * sites, but we can't control their order. If we mark a socket
+		 * as accounted, but the accounting functions are not patched in
+		 * yet, we'll lose accounting.
+		 *
+		 * We never race with the readers in sock_update_memcg(),
+		 * because when this value change, the code to process it is not
+		 * patched in yet.
+		 *
+		 * The activated bit is used to guarantee that no two writers
+		 * will do the update in the same memcg. Without that, we can't
+		 * properly shutdown the static key.
+		 */
+		if (!test_and_set_bit(MEMCG_SOCK_ACTIVATED, &cg_proto->flags))
+			static_key_slow_inc(&memcg_socket_limit_enabled);
+		set_bit(MEMCG_SOCK_ACTIVE, &cg_proto->flags);
+	}
 
 	return 0;
 }