Commit 6b6f3c71 authored by Kuniyuki Iwashima's avatar Kuniyuki Iwashima Committed by Jakub Kicinski
Browse files

af_unix: Simplify GC state. 



GC manages its state by two variables, unix_graph_maybe_cyclic
and unix_graph_grouped, both of which are set to false in the
initial state.

When an AF_UNIX socket is passed to an in-flight AF_UNIX socket,
unix_update_graph() sets unix_graph_maybe_cyclic to true and
unix_graph_grouped to false, making the next GC invocation call
unix_walk_scc() to group SCCs.

Once unix_walk_scc() finishes, sockets in the same SCC are linked
via vertex->scc_entry.  Then, unix_graph_grouped is set to true
so that the following GC invocations can skip Tarjan's algorithm
and simply iterate through the list in unix_walk_scc_fast().

In addition, if we know there is at least one cyclic reference,
we set unix_graph_maybe_cyclic to true so that we do not skip GC.

So the state transitions as follows:

  (unix_graph_maybe_cyclic, unix_graph_grouped)
  =
  (false, false) -> (true, false) -> (true, true) or (false, true)
                         ^.______________/________________/

There is no transition to the initial state where both variables
are false.

If we consider the initial state as grouped, we can see that the
GC actually has a tristate.

Let's consolidate two variables into one enum.

Signed-off-by: default avatarKuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20251115020935.2643121-3-kuniyu@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 58b47c71

net/unix/garbage.c

+12 −9
Original line number Diff line number Diff line
@@ -121,8 +121,13 @@ static struct unix_vertex *unix_edge_successor(struct unix_edge *edge) 
	return edge->successor->vertex;

}



static bool unix_graph_maybe_cyclic;

static bool unix_graph_grouped;

enum {

	UNIX_GRAPH_NOT_CYCLIC,

	UNIX_GRAPH_MAYBE_CYCLIC,

	UNIX_GRAPH_CYCLIC,

};



static unsigned char unix_graph_state;



static void unix_update_graph(struct unix_vertex *vertex)

{
@@ -132,8 +137,7 @@ static void unix_update_graph(struct unix_vertex *vertex) 
	if (!vertex)

		return;



	unix_graph_maybe_cyclic = true;

	unix_graph_grouped = false;

	unix_graph_state = UNIX_GRAPH_MAYBE_CYCLIC;

}



static LIST_HEAD(unix_unvisited_vertices);
@@ -536,8 +540,7 @@ static void unix_walk_scc(struct sk_buff_head *hitlist) 
	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;

	unix_graph_state = cyclic_sccs ? UNIX_GRAPH_CYCLIC : UNIX_GRAPH_NOT_CYCLIC;

}



static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
@@ -570,7 +573,7 @@ static void unix_walk_scc_fast(struct sk_buff_head *hitlist) 
	list_replace_init(&unix_visited_vertices, &unix_unvisited_vertices);



	unix_graph_cyclic_sccs = cyclic_sccs;

	unix_graph_maybe_cyclic = !!unix_graph_cyclic_sccs;

	unix_graph_state = cyclic_sccs ? UNIX_GRAPH_CYCLIC : UNIX_GRAPH_NOT_CYCLIC;

}



static bool gc_in_progress;
@@ -582,14 +585,14 @@ static void __unix_gc(struct work_struct *work) 


	spin_lock(&unix_gc_lock);



	if (!unix_graph_maybe_cyclic) {

	if (unix_graph_state == UNIX_GRAPH_NOT_CYCLIC) {

		spin_unlock(&unix_gc_lock);

		goto skip_gc;

	}



	__skb_queue_head_init(&hitlist);



	if (unix_graph_grouped)

	if (unix_graph_state == UNIX_GRAPH_CYCLIC)

		unix_walk_scc_fast(&hitlist);

	else

		unix_walk_scc(&hitlist);