1 files changed, 51 insertions, 28 deletions

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 816e8fa2b062..a7967a345827 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -318,6 +318,25 @@ void unix_destroy_fpl(struct scm_fp_list *fpl)
 	unix_free_vertices(fpl);
 }
 
+static bool gc_in_progress;
+static seqcount_t unix_peek_seq = SEQCNT_ZERO(unix_peek_seq);
+
+void unix_peek_fpl(struct scm_fp_list *fpl)
+{
+	static DEFINE_SPINLOCK(unix_peek_lock);
+
+	if (!fpl || !fpl->count_unix)
+		return;
+
+	if (!READ_ONCE(gc_in_progress))
+		return;
+
+	/* Invalidate the final refcnt check in unix_vertex_dead(). */
+	spin_lock(&unix_peek_lock);
+	raw_write_seqcount_barrier(&unix_peek_seq);
+	spin_unlock(&unix_peek_lock);
+}
+
 static bool unix_vertex_dead(struct unix_vertex *vertex)
 {
 	struct unix_edge *edge;
@@ -351,6 +370,36 @@ static bool unix_vertex_dead(struct unix_vertex *vertex)
 	return true;
 }
 
+static LIST_HEAD(unix_visited_vertices);
+static unsigned long unix_vertex_grouped_index = UNIX_VERTEX_INDEX_MARK2;
+
+static bool unix_scc_dead(struct list_head *scc, bool fast)
+{
+	struct unix_vertex *vertex;
+	bool scc_dead = true;
+	unsigned int seq;
+
+	seq = read_seqcount_begin(&unix_peek_seq);
+
+	list_for_each_entry_reverse(vertex, scc, scc_entry) {
+		/* Don't restart DFS from this vertex. */
+		list_move_tail(&vertex->entry, &unix_visited_vertices);
+
+		/* Mark vertex as off-stack for __unix_walk_scc(). */
+		if (!fast)
+			vertex->index = unix_vertex_grouped_index;
+
+		if (scc_dead)
+			scc_dead = unix_vertex_dead(vertex);
+	}
+
+	/* If MSG_PEEK intervened, defer this SCC to the next round. */
+	if (read_seqcount_retry(&unix_peek_seq, seq))
+		return false;
+
+	return scc_dead;
+}
+
 static void unix_collect_skb(struct list_head *scc, struct sk_buff_head *hitlist)
 {
 	struct unix_vertex *vertex;
@@ -404,9 +453,6 @@ static bool unix_scc_cyclic(struct list_head *scc)
 	return false;
 }
 
-static LIST_HEAD(unix_visited_vertices);
-static unsigned long unix_vertex_grouped_index = UNIX_VERTEX_INDEX_MARK2;
-
 static unsigned long __unix_walk_scc(struct unix_vertex *vertex,
 				     unsigned long *last_index,
 				     struct sk_buff_head *hitlist)
@@ -474,9 +520,7 @@ prev_vertex:
 	}
 
 	if (vertex->index == vertex->scc_index) {
-		struct unix_vertex *v;
 		struct list_head scc;
-		bool scc_dead = true;
 
 		/* SCC finalised.
 		 *
@@ -485,18 +529,7 @@ prev_vertex:
 		 */
 		__list_cut_position(&scc, &vertex_stack, &vertex->scc_entry);
 
-		list_for_each_entry_reverse(v, &scc, scc_entry) {
-			/* Don't restart DFS from this vertex in unix_walk_scc(). */
-			list_move_tail(&v->entry, &unix_visited_vertices);
-
-			/* Mark vertex as off-stack. */
-			v->index = unix_vertex_grouped_index;
-
-			if (scc_dead)
-				scc_dead = unix_vertex_dead(v);
-		}
-
-		if (scc_dead) {
+		if (unix_scc_dead(&scc, false)) {
 			unix_collect_skb(&scc, hitlist);
 		} else {
 			if (unix_vertex_max_scc_index < vertex->scc_index)
@@ -550,19 +583,11 @@ static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
 	while (!list_empty(&unix_unvisited_vertices)) {
 		struct unix_vertex *vertex;
 		struct list_head scc;
-		bool scc_dead = true;
 
 		vertex = list_first_entry(&unix_unvisited_vertices, typeof(*vertex), entry);
 		list_add(&scc, &vertex->scc_entry);
 
-		list_for_each_entry_reverse(vertex, &scc, scc_entry) {
-			list_move_tail(&vertex->entry, &unix_visited_vertices);
-
-			if (scc_dead)
-				scc_dead = unix_vertex_dead(vertex);
-		}
-
-		if (scc_dead) {
+		if (unix_scc_dead(&scc, true)) {
 			cyclic_sccs--;
 			unix_collect_skb(&scc, hitlist);
 		}
@@ -577,8 +602,6 @@ static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
 		   cyclic_sccs ? UNIX_GRAPH_CYCLIC : UNIX_GRAPH_NOT_CYCLIC);
 }
 
-static bool gc_in_progress;
-
 static void unix_gc(struct work_struct *work)
 {
 	struct sk_buff_head hitlist;