From 0fa7fa98dbcc2789409ed24e885485e645803d7f Mon Sep 17 00:00:00 2001 From: Pavel Emelyanov Date: Tue, 21 Aug 2012 01:06:47 +0000 Subject: packet: Protect packet sk list with mutex (v2) Change since v1: * Fixed inuse counters access spotted by Eric In patch eea68e2f (packet: Report socket mclist info via diag module) I've introduced a "scheduling in atomic" problem in packet diag module -- the socket list is traversed under rcu_read_lock() while performed under it sk mclist access requires rtnl lock (i.e. -- mutex) to be taken. [152363.820563] BUG: scheduling while atomic: crtools/12517/0x10000002 [152363.820573] 4 locks held by crtools/12517: [152363.820581] #0: (sock_diag_mutex){+.+.+.}, at: [] sock_diag_rcv+0x1f/0x3e [152363.820613] #1: (sock_diag_table_mutex){+.+.+.}, at: [] sock_diag_rcv_msg+0xdb/0x11a [152363.820644] #2: (nlk->cb_mutex){+.+.+.}, at: [] netlink_dump+0x23/0x1ab [152363.820693] #3: (rcu_read_lock){.+.+..}, at: [] packet_diag_dump+0x0/0x1af Similar thing was then re-introduced by further packet diag patches (fanount mutex and pgvec mutex for rings) :( Apart from being terribly sorry for the above, I propose to change the packet sk list protection from spinlock to mutex. This lock currently protects two modifications: * sklist * prot inuse counters The sklist modifications can be just reprotected with mutex since they already occur in a sleeping context. The inuse counters modifications are trickier -- the __this_cpu_-s are used inside, thus requiring the caller to handle the potential issues with contexts himself. Since packet sockets' counters are modified in two places only (packet_create and packet_release) we only need to protect the context from being preempted. BH disabling is not required in this case. Signed-off-by: Pavel Emelyanov Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- net/packet/af_packet.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) (limited to 'net/packet/af_packet.c') diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index bfaa0a83f0eb..f220c5bdb71f 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -2317,10 +2317,13 @@ static int packet_release(struct socket *sock) net = sock_net(sk); po = pkt_sk(sk); - spin_lock_bh(&net->packet.sklist_lock); + mutex_lock(&net->packet.sklist_lock); sk_del_node_init_rcu(sk); + mutex_unlock(&net->packet.sklist_lock); + + preempt_disable(); sock_prot_inuse_add(net, sk->sk_prot, -1); - spin_unlock_bh(&net->packet.sklist_lock); + preempt_enable(); spin_lock(&po->bind_lock); unregister_prot_hook(sk, false); @@ -2519,10 +2522,13 @@ static int packet_create(struct net *net, struct socket *sock, int protocol, register_prot_hook(sk); } - spin_lock_bh(&net->packet.sklist_lock); + mutex_lock(&net->packet.sklist_lock); sk_add_node_rcu(sk, &net->packet.sklist); + mutex_unlock(&net->packet.sklist_lock); + + preempt_disable(); sock_prot_inuse_add(net, &packet_proto, 1); - spin_unlock_bh(&net->packet.sklist_lock); + preempt_enable(); return 0; out: @@ -3775,7 +3781,7 @@ static const struct file_operations packet_seq_fops = { static int __net_init packet_net_init(struct net *net) { - spin_lock_init(&net->packet.sklist_lock); + mutex_init(&net->packet.sklist_lock); INIT_HLIST_HEAD(&net->packet.sklist); if (!proc_net_fops_create(net, "packet", 0, &packet_seq_fops)) -- cgit v1.2.3-55-g7522