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: [<ffffffff81a2dcb5>] sock_diag_rcv+0x1f/0x3e
[152363.820613] #1: (sock_diag_table_mutex){+.+.+.}, at: [<ffffffff81a2de70>] sock_diag_rcv_msg+0xdb/0x11a
[152363.820644] #2: (nlk->cb_mutex){+.+.+.}, at: [<ffffffff81a67d01>] netlink_dump+0x23/0x1ab
[152363.820693] #3: (rcu_read_lock){.+.+..}, at: [<ffffffff81b6a049>] 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 <xemul@parallels.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netns/packet.h b/include/net/netns/packet.h
index cb4e894..4780b08 100644
--- a/include/net/netns/packet.h
+++ b/include/net/netns/packet.h
@@ -8,7 +8,7 @@
#include <linux/spinlock.h>
struct netns_packet {
- spinlock_t sklist_lock;
+ struct mutex sklist_lock;
struct hlist_head sklist;
};
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index bfaa0a8..f220c5b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2317,10 +2317,13 @@
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 @@
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 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))
diff --git a/net/packet/diag.c b/net/packet/diag.c
index bc33fbe..39bce0d 100644
--- a/net/packet/diag.c
+++ b/net/packet/diag.c
@@ -177,8 +177,8 @@
net = sock_net(skb->sk);
req = nlmsg_data(cb->nlh);
- rcu_read_lock();
- sk_for_each_rcu(sk, node, &net->packet.sklist) {
+ mutex_lock(&net->packet.sklist_lock);
+ sk_for_each(sk, node, &net->packet.sklist) {
if (!net_eq(sock_net(sk), net))
continue;
if (num < s_num)
@@ -192,7 +192,7 @@
num++;
}
done:
- rcu_read_unlock();
+ mutex_unlock(&net->packet.sklist_lock);
cb->args[0] = num;
return skb->len;