af_unix: Count cyclic SCC.

__unix_walk_scc() and unix_walk_scc_fast() call unix_scc_cyclic()
for each SCC to check if it forms a cyclic reference, so that we
can skip GC at the following invocations in case all SCCs do not
have any cycles.

If we count the number of cyclic SCCs in __unix_walk_scc(), we can
simplify unix_walk_scc_fast() because the number of cyclic SCCs
only changes when it garbage-collects a SCC.

So, let's count cyclic SCC in __unix_walk_scc() and decrement it
in unix_walk_scc_fast() when performing garbage collection.

Note that we will use this counter in a later patch to check if a
cycle existed in the previous GC run.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20251115020935.2643121-2-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 65396a4e1b07e6082e945aed7782c1daa89ab9cc..9f62d5097973542ffc3a3ed0cc094ec88ac1f250 100644 (file)
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -404,9 +404,11 @@ static bool unix_scc_cyclic(struct list_head *scc)
 static LIST_HEAD(unix_visited_vertices);
 static unsigned long unix_vertex_grouped_index = UNIX_VERTEX_INDEX_MARK2;
 
-static void __unix_walk_scc(struct unix_vertex *vertex, unsigned long *last_index,
-                           struct sk_buff_head *hitlist)
+static unsigned long __unix_walk_scc(struct unix_vertex *vertex,
+                                    unsigned long *last_index,
+                                    struct sk_buff_head *hitlist)
 {
+       unsigned long cyclic_sccs = 0;
        LIST_HEAD(vertex_stack);
        struct unix_edge *edge;
        LIST_HEAD(edge_stack);
@@ -497,8 +499,8 @@ prev_vertex:
                        if (unix_vertex_max_scc_index < vertex->scc_index)
                                unix_vertex_max_scc_index = vertex->scc_index;
 
-                       if (!unix_graph_maybe_cyclic)
-                               unix_graph_maybe_cyclic = unix_scc_cyclic(&scc);
+                       if (unix_scc_cyclic(&scc))
+                               cyclic_sccs++;
                }
 
                list_del(&scc);
@@ -507,13 +509,17 @@ prev_vertex:
        /* Need backtracking ? */
        if (!list_empty(&edge_stack))
                goto prev_vertex;
+
+       return cyclic_sccs;
 }
 
+static unsigned long unix_graph_cyclic_sccs;
+
 static void unix_walk_scc(struct sk_buff_head *hitlist)
 {
        unsigned long last_index = UNIX_VERTEX_INDEX_START;
+       unsigned long cyclic_sccs = 0;
 
-       unix_graph_maybe_cyclic = false;
        unix_vertex_max_scc_index = UNIX_VERTEX_INDEX_START;
 
        /* Visit every vertex exactly once.
@@ -523,18 +529,20 @@ static void unix_walk_scc(struct sk_buff_head *hitlist)
                struct unix_vertex *vertex;
 
                vertex = list_first_entry(&unix_unvisited_vertices, typeof(*vertex), entry);
-               __unix_walk_scc(vertex, &last_index, hitlist);
+               cyclic_sccs += __unix_walk_scc(vertex, &last_index, hitlist);
        }
 
        list_replace_init(&unix_visited_vertices, &unix_unvisited_vertices);
        swap(unix_vertex_unvisited_index, unix_vertex_grouped_index);
 
+       unix_graph_cyclic_sccs = cyclic_sccs;
+       unix_graph_maybe_cyclic = !!unix_graph_cyclic_sccs;
        unix_graph_grouped = true;
 }
 
 static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
 {
-       unix_graph_maybe_cyclic = false;
+       unsigned long cyclic_sccs = unix_graph_cyclic_sccs;
 
        while (!list_empty(&unix_unvisited_vertices)) {
                struct unix_vertex *vertex;
@@ -551,15 +559,18 @@ static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
                                scc_dead = unix_vertex_dead(vertex);
                }
 
-               if (scc_dead)
+               if (scc_dead) {
+                       cyclic_sccs--;
                        unix_collect_skb(&scc, hitlist);
-               else if (!unix_graph_maybe_cyclic)
-                       unix_graph_maybe_cyclic = unix_scc_cyclic(&scc);
+               }
 
                list_del(&scc);
        }
 
        list_replace_init(&unix_visited_vertices, &unix_unvisited_vertices);
+
+       unix_graph_cyclic_sccs = cyclic_sccs;
+       unix_graph_maybe_cyclic = !!unix_graph_cyclic_sccs;
 }
 
 static bool gc_in_progress;