From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5C044226CF0; Mon, 2 Jun 2025 14:24:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748874259; cv=none; b=fb3dCa9++4aEhGzOF4h5CF5CCEI+fcJOZQtVFQFPJ5pXFb4A0/s/TAJ0OrXLvwL4+Q8vBq42/JJZNmZX3NDwDoahwoT7H72pTBROi7Z8HlDe+n2Rx3keJwyq3KVkaW3B0n0MwY2WvMrB21twGAaad4JD7pndEDKvWXpFEKyCw+k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748874259; c=relaxed/simple; bh=9thmBb0HdXF/5srtVzF9ojyONfEz3nmct0lY4zIcKZY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jmngl2+ALJN+mlJCpQQE/7zoakdIZVx+O8mXe7oqlvDshndc8sAh1g4vVSzSm+eTmmeXAyEh0O+ReRA5+nsMuQZ0wLCYDTkxLycxejVAfe8/ju2imehgy9+y38TJVKKzYW/6IkcP+H6HNYY9FQGlYDjbxtdNS0vs1TVckLB+PzM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Z8lNFEVD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Z8lNFEVD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 749DBC4CEEB; Mon, 2 Jun 2025 14:24:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1748874256; bh=9thmBb0HdXF/5srtVzF9ojyONfEz3nmct0lY4zIcKZY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Z8lNFEVDc1eQtDOFwlNq+WkG0Q3oOvRJ4Qk9vZ+T/om5WGS/sagv7+fpZjvJObGCy 8G0ti1/FLtScqeqykM+NRSyMC9Ktqg4E8ZTgU+PdgT2zhs3nHnDtWYUiL7fWpYGuiK xIKQWSLjfWlEtly+eYfhiznMWSUJG8ASpq1+EBa4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Kuniyuki Iwashima , Paolo Abeni , Jakub Kicinski , Lee Jones Subject: [PATCH 6.6 410/444] af_unix: Skip GC if no cycle exists. Date: Mon, 2 Jun 2025 15:47:54 +0200 Message-ID: <20250602134357.575465324@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250602134340.906731340@linuxfoundation.org> References: <20250602134340.906731340@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kuniyuki Iwashima commit 77e5593aebba823bcbcf2c4b58b07efcd63933b8 upstream. We do not need to run GC if there is no possible cyclic reference. We use unix_graph_maybe_cyclic to decide if we should run GC. If a fd of an AF_UNIX socket is passed to an already inflight AF_UNIX socket, they could form a cyclic reference. Then, we set true to unix_graph_maybe_cyclic and later run Tarjan's algorithm to group them into SCC. Once we run Tarjan's algorithm, we are 100% sure whether cyclic references exist or not. If there is no cycle, we set false to unix_graph_maybe_cyclic and can skip the entire garbage collection next time. When finalising SCC, we set true to unix_graph_maybe_cyclic if SCC consists of multiple vertices. Even if SCC is a single vertex, a cycle might exist as self-fd passing. Given the corner case is rare, we detect it by checking all edges of the vertex and set true to unix_graph_maybe_cyclic. With this change, __unix_gc() is just a spin_lock() dance in the normal usage. Signed-off-by: Kuniyuki Iwashima Acked-by: Paolo Abeni Link: https://lore.kernel.org/r/20240325202425.60930-11-kuniyu@amazon.com Signed-off-by: Jakub Kicinski Signed-off-by: Lee Jones Signed-off-by: Greg Kroah-Hartman --- net/unix/garbage.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 47 insertions(+), 1 deletion(-) --- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -112,6 +112,19 @@ static struct unix_vertex *unix_edge_suc return edge->successor->vertex; } +static bool unix_graph_maybe_cyclic; + +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; +} + static LIST_HEAD(unix_unvisited_vertices); enum unix_vertex_index { @@ -138,12 +151,16 @@ static void unix_add_edge(struct scm_fp_ vertex->out_degree++; list_add_tail(&edge->vertex_entry, &vertex->edges); + + unix_update_graph(unix_edge_successor(edge)); } static void unix_del_edge(struct scm_fp_list *fpl, struct unix_edge *edge) { struct unix_vertex *vertex = edge->predecessor->vertex; + unix_update_graph(unix_edge_successor(edge)); + list_del(&edge->vertex_entry); vertex->out_degree--; @@ -227,6 +244,7 @@ out: void unix_update_edges(struct unix_sock *receiver) { spin_lock(&unix_gc_lock); + unix_update_graph(unix_sk(receiver->listener)->vertex); receiver->listener = NULL; spin_unlock(&unix_gc_lock); } @@ -268,6 +286,26 @@ void unix_destroy_fpl(struct scm_fp_list unix_free_vertices(fpl); } +static bool unix_scc_cyclic(struct list_head *scc) +{ + struct unix_vertex *vertex; + struct unix_edge *edge; + + /* 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; @@ -353,6 +391,9 @@ prev_vertex: vertex->index = unix_vertex_grouped_index; } + if (!unix_graph_maybe_cyclic) + unix_graph_maybe_cyclic = unix_scc_cyclic(&scc); + list_del(&scc); } @@ -363,6 +404,8 @@ prev_vertex: static void unix_walk_scc(void) { + unix_graph_maybe_cyclic = false; + /* Visit every vertex exactly once. * __unix_walk_scc() moves visited vertices to unix_visited_vertices. */ @@ -524,6 +567,9 @@ static void __unix_gc(struct work_struct spin_lock(&unix_gc_lock); + if (!unix_graph_maybe_cyclic) + goto skip_gc; + unix_walk_scc(); /* First, select candidates for garbage collection. Only @@ -633,7 +679,7 @@ static void __unix_gc(struct work_struct /* All candidates should have been detached by now. */ WARN_ON_ONCE(!list_empty(&gc_candidates)); - +skip_gc: /* Paired with READ_ONCE() in wait_for_unix_gc(). */ WRITE_ONCE(gc_in_progress, false);