1 files changed, 481 insertions, 191 deletions

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 2405f0f9af31..1f8b8cdfcdc8 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -81,255 +81,545 @@
 #include <net/scm.h>
 #include <net/tcp_states.h>
 
-#include "scm.h"
+struct unix_sock *unix_get_socket(struct file *filp)
+{
+	struct inode *inode = file_inode(filp);
+
+	/* Socket ? */
+	if (S_ISSOCK(inode->i_mode) && !(filp->f_mode & FMODE_PATH)) {
+		struct socket *sock = SOCKET_I(inode);
+		const struct proto_ops *ops;
+		struct sock *sk = sock->sk;
 
-/* Internal data structures and random procedures: */
+		ops = READ_ONCE(sock->ops);
 
-static LIST_HEAD(gc_candidates);
-static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
+		/* PF_UNIX ? */
+		if (sk && ops && ops->family == PF_UNIX)
+			return unix_sk(sk);
+	}
 
-static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
-			  struct sk_buff_head *hitlist)
+	return NULL;
+}
+
+static struct unix_vertex *unix_edge_successor(struct unix_edge *edge)
 {
-	struct sk_buff *skb;
-	struct sk_buff *next;
-
-	spin_lock(&x->sk_receive_queue.lock);
-	skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
-		/* Do we have file descriptors ? */
-		if (UNIXCB(skb).fp) {
-			bool hit = false;
-			/* Process the descriptors of this socket */
-			int nfd = UNIXCB(skb).fp->count;
-			struct file **fp = UNIXCB(skb).fp->fp;
-
-			while (nfd--) {
-				/* Get the socket the fd matches if it indeed does so */
-				struct sock *sk = unix_get_socket(*fp++);
-
-				if (sk) {
-					struct unix_sock *u = unix_sk(sk);
-
-					/* Ignore non-candidates, they could
-					 * have been added to the queues after
-					 * starting the garbage collection
-					 */
-					if (test_bit(UNIX_GC_CANDIDATE, &u->gc_flags)) {
-						hit = true;
-
-						func(u);
-					}
-				}
-			}
-			if (hit && hitlist != NULL) {
-				__skb_unlink(skb, &x->sk_receive_queue);
-				__skb_queue_tail(hitlist, skb);
-			}
-		}
+	/* If an embryo socket has a fd,
+	 * the listener indirectly holds the fd's refcnt.
+	 */
+	if (edge->successor->listener)
+		return unix_sk(edge->successor->listener)->vertex;
+
+	return edge->successor->vertex;
+}
+
+static bool unix_graph_maybe_cyclic;
+static bool unix_graph_grouped;
+
+static void unix_update_graph(struct unix_vertex *vertex)
+{
+	/* If the receiver socket is not inflight, no cyclic
+	 * reference could be formed.
+	 */
+	if (!vertex)
+		return;
+
+	unix_graph_maybe_cyclic = true;
+	unix_graph_grouped = false;
+}
+
+static LIST_HEAD(unix_unvisited_vertices);
+
+enum unix_vertex_index {
+	UNIX_VERTEX_INDEX_MARK1,
+	UNIX_VERTEX_INDEX_MARK2,
+	UNIX_VERTEX_INDEX_START,
+};
+
+static unsigned long unix_vertex_unvisited_index = UNIX_VERTEX_INDEX_MARK1;
+
+static void unix_add_edge(struct scm_fp_list *fpl, struct unix_edge *edge)
+{
+	struct unix_vertex *vertex = edge->predecessor->vertex;
+
+	if (!vertex) {
+		vertex = list_first_entry(&fpl->vertices, typeof(*vertex), entry);
+		vertex->index = unix_vertex_unvisited_index;
+		vertex->out_degree = 0;
+		INIT_LIST_HEAD(&vertex->edges);
+		INIT_LIST_HEAD(&vertex->scc_entry);
+
+		list_move_tail(&vertex->entry, &unix_unvisited_vertices);
+		edge->predecessor->vertex = vertex;
 	}
-	spin_unlock(&x->sk_receive_queue.lock);
+
+	vertex->out_degree++;
+	list_add_tail(&edge->vertex_entry, &vertex->edges);
+
+	unix_update_graph(unix_edge_successor(edge));
 }
 
-static void scan_children(struct sock *x, void (*func)(struct unix_sock *),
-			  struct sk_buff_head *hitlist)
+static void unix_del_edge(struct scm_fp_list *fpl, struct unix_edge *edge)
 {
-	if (x->sk_state != TCP_LISTEN) {
-		scan_inflight(x, func, hitlist);
-	} else {
-		struct sk_buff *skb;
-		struct sk_buff *next;
-		struct unix_sock *u;
-		LIST_HEAD(embryos);
+	struct unix_vertex *vertex = edge->predecessor->vertex;
 
-		/* For a listening socket collect the queued embryos
-		 * and perform a scan on them as well.
-		 */
-		spin_lock(&x->sk_receive_queue.lock);
-		skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
-			u = unix_sk(skb->sk);
+	if (!fpl->dead)
+		unix_update_graph(unix_edge_successor(edge));
 
-			/* An embryo cannot be in-flight, so it's safe
-			 * to use the list link.
-			 */
-			BUG_ON(!list_empty(&u->link));
-			list_add_tail(&u->link, &embryos);
-		}
-		spin_unlock(&x->sk_receive_queue.lock);
+	list_del(&edge->vertex_entry);
+	vertex->out_degree--;
 
-		while (!list_empty(&embryos)) {
-			u = list_entry(embryos.next, struct unix_sock, link);
-			scan_inflight(&u->sk, func, hitlist);
-			list_del_init(&u->link);
-		}
+	if (!vertex->out_degree) {
+		edge->predecessor->vertex = NULL;
+		list_move_tail(&vertex->entry, &fpl->vertices);
 	}
 }
 
-static void dec_inflight(struct unix_sock *usk)
+static void unix_free_vertices(struct scm_fp_list *fpl)
 {
-	atomic_long_dec(&usk->inflight);
+	struct unix_vertex *vertex, *next_vertex;
+
+	list_for_each_entry_safe(vertex, next_vertex, &fpl->vertices, entry) {
+		list_del(&vertex->entry);
+		kfree(vertex);
+	}
 }
 
-static void inc_inflight(struct unix_sock *usk)
+static DEFINE_SPINLOCK(unix_gc_lock);
+unsigned int unix_tot_inflight;
+
+void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver)
 {
-	atomic_long_inc(&usk->inflight);
+	int i = 0, j = 0;
+
+	spin_lock(&unix_gc_lock);
+
+	if (!fpl->count_unix)
+		goto out;
+
+	do {
+		struct unix_sock *inflight = unix_get_socket(fpl->fp[j++]);
+		struct unix_edge *edge;
+
+		if (!inflight)
+			continue;
+
+		edge = fpl->edges + i++;
+		edge->predecessor = inflight;
+		edge->successor = receiver;
+
+		unix_add_edge(fpl, edge);
+	} while (i < fpl->count_unix);
+
+	receiver->scm_stat.nr_unix_fds += fpl->count_unix;
+	WRITE_ONCE(unix_tot_inflight, unix_tot_inflight + fpl->count_unix);
+out:
+	WRITE_ONCE(fpl->user->unix_inflight, fpl->user->unix_inflight + fpl->count);
+
+	spin_unlock(&unix_gc_lock);
+
+	fpl->inflight = true;
+
+	unix_free_vertices(fpl);
 }
 
-static void inc_inflight_move_tail(struct unix_sock *u)
+void unix_del_edges(struct scm_fp_list *fpl)
 {
-	atomic_long_inc(&u->inflight);
-	/* If this still might be part of a cycle, move it to the end
-	 * of the list, so that it's checked even if it was already
-	 * passed over
+	struct unix_sock *receiver;
+	int i = 0;
+
+	spin_lock(&unix_gc_lock);
+
+	if (!fpl->count_unix)
+		goto out;
+
+	do {
+		struct unix_edge *edge = fpl->edges + i++;
+
+		unix_del_edge(fpl, edge);
+	} while (i < fpl->count_unix);
+
+	if (!fpl->dead) {
+		receiver = fpl->edges[0].successor;
+		receiver->scm_stat.nr_unix_fds -= fpl->count_unix;
+	}
+	WRITE_ONCE(unix_tot_inflight, unix_tot_inflight - fpl->count_unix);
+out:
+	WRITE_ONCE(fpl->user->unix_inflight, fpl->user->unix_inflight - fpl->count);
+
+	spin_unlock(&unix_gc_lock);
+
+	fpl->inflight = false;
+}
+
+void unix_update_edges(struct unix_sock *receiver)
+{
+	/* nr_unix_fds is only updated under unix_state_lock().
+	 * If it's 0 here, the embryo socket is not part of the
+	 * inflight graph, and GC will not see it, so no lock needed.
 	 */
-	if (test_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags))
-		list_move_tail(&u->link, &gc_candidates);
+	if (!receiver->scm_stat.nr_unix_fds) {
+		receiver->listener = NULL;
+	} else {
+		spin_lock(&unix_gc_lock);
+		unix_update_graph(unix_sk(receiver->listener)->vertex);
+		receiver->listener = NULL;
+		spin_unlock(&unix_gc_lock);
+	}
 }
 
-static bool gc_in_progress;
-#define UNIX_INFLIGHT_TRIGGER_GC 16000
+int unix_prepare_fpl(struct scm_fp_list *fpl)
+{
+	struct unix_vertex *vertex;
+	int i;
+
+	if (!fpl->count_unix)
+		return 0;
 
-void wait_for_unix_gc(void)
+	for (i = 0; i < fpl->count_unix; i++) {
+		vertex = kmalloc(sizeof(*vertex), GFP_KERNEL);
+		if (!vertex)
+			goto err;
+
+		list_add(&vertex->entry, &fpl->vertices);
+	}
+
+	fpl->edges = kvmalloc_array(fpl->count_unix, sizeof(*fpl->edges),
+				    GFP_KERNEL_ACCOUNT);
+	if (!fpl->edges)
+		goto err;
+
+	return 0;
+
+err:
+	unix_free_vertices(fpl);
+	return -ENOMEM;
+}
+
+void unix_destroy_fpl(struct scm_fp_list *fpl)
 {
-	/* If number of inflight sockets is insane,
-	 * force a garbage collect right now.
-	 * Paired with the WRITE_ONCE() in unix_inflight(),
-	 * unix_notinflight() and gc_in_progress().
-	 */
-	if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC &&
-	    !READ_ONCE(gc_in_progress))
-		unix_gc();
-	wait_event(unix_gc_wait, gc_in_progress == false);
+	if (fpl->inflight)
+		unix_del_edges(fpl);
+
+	kvfree(fpl->edges);
+	unix_free_vertices(fpl);
 }
 
-/* The external entry point: unix_gc() */
-void unix_gc(void)
+static bool unix_vertex_dead(struct unix_vertex *vertex)
 {
-	struct sk_buff *next_skb, *skb;
+	struct unix_edge *edge;
 	struct unix_sock *u;
-	struct unix_sock *next;
-	struct sk_buff_head hitlist;
-	struct list_head cursor;
-	LIST_HEAD(not_cycle_list);
+	long total_ref;
 
-	spin_lock(&unix_gc_lock);
+	list_for_each_entry(edge, &vertex->edges, vertex_entry) {
+		struct unix_vertex *next_vertex = unix_edge_successor(edge);
 
-	/* Avoid a recursive GC. */
-	if (gc_in_progress)
-		goto out;
+		/* The vertex's fd can be received by a non-inflight socket. */
+		if (!next_vertex)
+			return false;
 
-	/* Paired with READ_ONCE() in wait_for_unix_gc(). */
-	WRITE_ONCE(gc_in_progress, true);
+		/* The vertex's fd can be received by an inflight socket in
+		 * another SCC.
+		 */
+		if (next_vertex->scc_index != vertex->scc_index)
+			return false;
+	}
 
-	/* First, select candidates for garbage collection.  Only
-	 * in-flight sockets are considered, and from those only ones
-	 * which don't have any external reference.
-	 *
-	 * Holding unix_gc_lock will protect these candidates from
-	 * being detached, and hence from gaining an external
-	 * reference.  Since there are no possible receivers, all
-	 * buffers currently on the candidates' queues stay there
-	 * during the garbage collection.
-	 *
-	 * We also know that no new candidate can be added onto the
-	 * receive queues.  Other, non candidate sockets _can_ be
-	 * added to queue, so we must make sure only to touch
-	 * candidates.
-	 */
-	list_for_each_entry_safe(u, next, &gc_inflight_list, link) {
-		long total_refs;
-		long inflight_refs;
-
-		total_refs = file_count(u->sk.sk_socket->file);
-		inflight_refs = atomic_long_read(&u->inflight);
-
-		BUG_ON(inflight_refs < 1);
-		BUG_ON(total_refs < inflight_refs);
-		if (total_refs == inflight_refs) {
-			list_move_tail(&u->link, &gc_candidates);
-			__set_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
-			__set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
+	/* No receiver exists out of the same SCC. */
+
+	edge = list_first_entry(&vertex->edges, typeof(*edge), vertex_entry);
+	u = edge->predecessor;
+	total_ref = file_count(u->sk.sk_socket->file);
+
+	/* If not close()d, total_ref > out_degree. */
+	if (total_ref != vertex->out_degree)
+		return false;
+
+	return true;
+}
+
+enum unix_recv_queue_lock_class {
+	U_RECVQ_LOCK_NORMAL,
+	U_RECVQ_LOCK_EMBRYO,
+};
+
+static void unix_collect_skb(struct list_head *scc, struct sk_buff_head *hitlist)
+{
+	struct unix_vertex *vertex;
+
+	list_for_each_entry_reverse(vertex, scc, scc_entry) {
+		struct sk_buff_head *queue;
+		struct unix_edge *edge;
+		struct unix_sock *u;
+
+		edge = list_first_entry(&vertex->edges, typeof(*edge), vertex_entry);
+		u = edge->predecessor;
+		queue = &u->sk.sk_receive_queue;
+
+		spin_lock(&queue->lock);
+
+		if (u->sk.sk_state == TCP_LISTEN) {
+			struct sk_buff *skb;
+
+			skb_queue_walk(queue, skb) {
+				struct sk_buff_head *embryo_queue = &skb->sk->sk_receive_queue;
+
+				/* listener -> embryo order, the inversion never happens. */
+				spin_lock_nested(&embryo_queue->lock, U_RECVQ_LOCK_EMBRYO);
+				skb_queue_splice_init(embryo_queue, hitlist);
+				spin_unlock(&embryo_queue->lock);
+			}
+		} else {
+			skb_queue_splice_init(queue, hitlist);
+
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+			if (u->oob_skb) {
+				kfree_skb(u->oob_skb);
+				u->oob_skb = NULL;
+			}
+#endif
 		}
+
+		spin_unlock(&queue->lock);
 	}
+}
 
-	/* Now remove all internal in-flight reference to children of
-	 * the candidates.
-	 */
-	list_for_each_entry(u, &gc_candidates, link)
-		scan_children(&u->sk, dec_inflight, NULL);
+static bool unix_scc_cyclic(struct list_head *scc)
+{
+	struct unix_vertex *vertex;
+	struct unix_edge *edge;
 
-	/* Restore the references for children of all candidates,
-	 * which have remaining references.  Do this recursively, so
-	 * only those remain, which form cyclic references.
-	 *
-	 * Use a "cursor" link, to make the list traversal safe, even
-	 * though elements might be moved about.
+	/* SCC containing multiple vertices ? */
+	if (!list_is_singular(scc))
+		return true;
+
+	vertex = list_first_entry(scc, typeof(*vertex), scc_entry);
+
+	/* Self-reference or a embryo-listener circle ? */
+	list_for_each_entry(edge, &vertex->edges, vertex_entry) {
+		if (unix_edge_successor(edge) == vertex)
+			return true;
+	}
+
+	return false;
+}
+
+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)
+{
+	LIST_HEAD(vertex_stack);
+	struct unix_edge *edge;
+	LIST_HEAD(edge_stack);
+
+next_vertex:
+	/* Push vertex to vertex_stack and mark it as on-stack
+	 * (index >= UNIX_VERTEX_INDEX_START).
+	 * The vertex will be popped when finalising SCC later.
 	 */
-	list_add(&cursor, &gc_candidates);
-	while (cursor.next != &gc_candidates) {
-		u = list_entry(cursor.next, struct unix_sock, link);
+	list_add(&vertex->scc_entry, &vertex_stack);
 
-		/* Move cursor to after the current position. */
-		list_move(&cursor, &u->link);
+	vertex->index = *last_index;
+	vertex->scc_index = *last_index;
+	(*last_index)++;
 
-		if (atomic_long_read(&u->inflight) > 0) {
-			list_move_tail(&u->link, &not_cycle_list);
-			__clear_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
-			scan_children(&u->sk, inc_inflight_move_tail, NULL);
+	/* Explore neighbour vertices (receivers of the current vertex's fd). */
+	list_for_each_entry(edge, &vertex->edges, vertex_entry) {
+		struct unix_vertex *next_vertex = unix_edge_successor(edge);
+
+		if (!next_vertex)
+			continue;
+
+		if (next_vertex->index == unix_vertex_unvisited_index) {
+			/* Iterative deepening depth first search
+			 *
+			 *   1. Push a forward edge to edge_stack and set
+			 *      the successor to vertex for the next iteration.
+			 */
+			list_add(&edge->stack_entry, &edge_stack);
+
+			vertex = next_vertex;
+			goto next_vertex;
+
+			/*   2. Pop the edge directed to the current vertex
+			 *      and restore the ancestor for backtracking.
+			 */
+prev_vertex:
+			edge = list_first_entry(&edge_stack, typeof(*edge), stack_entry);
+			list_del_init(&edge->stack_entry);
+
+			next_vertex = vertex;
+			vertex = edge->predecessor->vertex;
+
+			/* If the successor has a smaller scc_index, two vertices
+			 * are in the same SCC, so propagate the smaller scc_index
+			 * to skip SCC finalisation.
+			 */
+			vertex->scc_index = min(vertex->scc_index, next_vertex->scc_index);
+		} else if (next_vertex->index != unix_vertex_grouped_index) {
+			/* Loop detected by a back/cross edge.
+			 *
+			 * The successor is on vertex_stack, so two vertices are in
+			 * the same SCC.  If the successor has a smaller *scc_index*,
+			 * propagate it to skip SCC finalisation.
+			 */
+			vertex->scc_index = min(vertex->scc_index, next_vertex->scc_index);
+		} else {
+			/* The successor was already grouped as another SCC */
 		}
 	}
-	list_del(&cursor);
 
-	/* Now gc_candidates contains only garbage.  Restore original
-	 * inflight counters for these as well, and remove the skbuffs
-	 * which are creating the cycle(s).
-	 */
-	skb_queue_head_init(&hitlist);
-	list_for_each_entry(u, &gc_candidates, link)
-		scan_children(&u->sk, inc_inflight, &hitlist);
+	if (vertex->index == vertex->scc_index) {
+		struct list_head scc;
+		bool scc_dead = true;
 
-	/* not_cycle_list contains those sockets which do not make up a
-	 * cycle.  Restore these to the inflight list.
-	 */
-	while (!list_empty(&not_cycle_list)) {
-		u = list_entry(not_cycle_list.next, struct unix_sock, link);
-		__clear_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
-		list_move_tail(&u->link, &gc_inflight_list);
+		/* SCC finalised.
+		 *
+		 * If the scc_index was not updated, all the vertices above on
+		 * vertex_stack are in the same SCC.  Group them using scc_entry.
+		 */
+		__list_cut_position(&scc, &vertex_stack, &vertex->scc_entry);
+
+		list_for_each_entry_reverse(vertex, &scc, scc_entry) {
+			/* Don't restart DFS from this vertex in unix_walk_scc(). */
+			list_move_tail(&vertex->entry, &unix_visited_vertices);
+
+			/* Mark vertex as off-stack. */
+			vertex->index = unix_vertex_grouped_index;
+
+			if (scc_dead)
+				scc_dead = unix_vertex_dead(vertex);
+		}
+
+		if (scc_dead)
+			unix_collect_skb(&scc, hitlist);
+		else if (!unix_graph_maybe_cyclic)
+			unix_graph_maybe_cyclic = unix_scc_cyclic(&scc);
+
+		list_del(&scc);
 	}
 
-	spin_unlock(&unix_gc_lock);
+	/* Need backtracking ? */
+	if (!list_empty(&edge_stack))
+		goto prev_vertex;
+}
+
+static void unix_walk_scc(struct sk_buff_head *hitlist)
+{
+	unsigned long last_index = UNIX_VERTEX_INDEX_START;
+
+	unix_graph_maybe_cyclic = false;
 
-	/* We need io_uring to clean its registered files, ignore all io_uring
-	 * originated skbs. It's fine as io_uring doesn't keep references to
-	 * other io_uring instances and so killing all other files in the cycle
-	 * will put all io_uring references forcing it to go through normal
-	 * release.path eventually putting registered files.
+	/* Visit every vertex exactly once.
+	 * __unix_walk_scc() moves visited vertices to unix_visited_vertices.
 	 */
-	skb_queue_walk_safe(&hitlist, skb, next_skb) {
-		if (skb->destructor == io_uring_destruct_scm) {
-			__skb_unlink(skb, &hitlist);
-			skb_queue_tail(&skb->sk->sk_receive_queue, skb);
+	while (!list_empty(&unix_unvisited_vertices)) {
+		struct unix_vertex *vertex;
+
+		vertex = list_first_entry(&unix_unvisited_vertices, typeof(*vertex), entry);
+		__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_grouped = true;
+}
+
+static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
+{
+	unix_graph_maybe_cyclic = false;
+
+	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)
+			unix_collect_skb(&scc, hitlist);
+		else if (!unix_graph_maybe_cyclic)
+			unix_graph_maybe_cyclic = unix_scc_cyclic(&scc);
+
+		list_del(&scc);
 	}
 
-	/* Here we are. Hitlist is filled. Die. */
-	__skb_queue_purge(&hitlist);
+	list_replace_init(&unix_visited_vertices, &unix_unvisited_vertices);
+}
+
+static bool gc_in_progress;
+
+static void __unix_gc(struct work_struct *work)
+{
+	struct sk_buff_head hitlist;
+	struct sk_buff *skb;
 
 	spin_lock(&unix_gc_lock);
 
-	/* There could be io_uring registered files, just push them back to
-	 * the inflight list
-	 */
-	list_for_each_entry_safe(u, next, &gc_candidates, link)
-		list_move_tail(&u->link, &gc_inflight_list);
+	if (!unix_graph_maybe_cyclic) {
+		spin_unlock(&unix_gc_lock);
+		goto skip_gc;
+	}
 
-	/* All candidates should have been detached by now. */
-	BUG_ON(!list_empty(&gc_candidates));
+	__skb_queue_head_init(&hitlist);
+
+	if (unix_graph_grouped)
+		unix_walk_scc_fast(&hitlist);
+	else
+		unix_walk_scc(&hitlist);
+
+	spin_unlock(&unix_gc_lock);
 
-	/* Paired with READ_ONCE() in wait_for_unix_gc(). */
+	skb_queue_walk(&hitlist, skb) {
+		if (UNIXCB(skb).fp)
+			UNIXCB(skb).fp->dead = true;
+	}
+
+	__skb_queue_purge(&hitlist);
+skip_gc:
 	WRITE_ONCE(gc_in_progress, false);
+}
 
-	wake_up(&unix_gc_wait);
+static DECLARE_WORK(unix_gc_work, __unix_gc);
 
- out:
-	spin_unlock(&unix_gc_lock);
+void unix_gc(void)
+{
+	WRITE_ONCE(gc_in_progress, true);
+	queue_work(system_unbound_wq, &unix_gc_work);
+}
+
+#define UNIX_INFLIGHT_TRIGGER_GC 16000
+#define UNIX_INFLIGHT_SANE_USER (SCM_MAX_FD * 8)
+
+void wait_for_unix_gc(struct scm_fp_list *fpl)
+{
+	/* If number of inflight sockets is insane,
+	 * force a garbage collect right now.
+	 *
+	 * Paired with the WRITE_ONCE() in unix_inflight(),
+	 * unix_notinflight(), and __unix_gc().
+	 */
+	if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC &&
+	    !READ_ONCE(gc_in_progress))
+		unix_gc();
+
+	/* Penalise users who want to send AF_UNIX sockets
+	 * but whose sockets have not been received yet.
+	 */
+	if (!fpl || !fpl->count_unix ||
+	    READ_ONCE(fpl->user->unix_inflight) < UNIX_INFLIGHT_SANE_USER)
+		return;
+
+	if (READ_ONCE(gc_in_progress))
+		flush_work(&unix_gc_work);
 }