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Commit 0fa7fa98 authored by Pavel Emelyanov's avatar Pavel Emelyanov Committed by David S. Miller
Browse files

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: default avatarPavel Emelyanov <xemul@parallels.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b32607dd

include/net/netns/packet.h

+1 −1
Original line number Diff line number Diff line
@@ -8,7 +8,7 @@ 
#include <linux/spinlock.h>



struct netns_packet {

	spinlock_t		sklist_lock;

	struct mutex		sklist_lock;

	struct hlist_head	sklist;

};

net/packet/af_packet.c

+11 −5
Original line number Diff line number Diff line
@@ -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))

net/packet/diag.c

+3 −3
Original line number Diff line number Diff line
@@ -177,8 +177,8 @@ static int packet_diag_dump(struct sk_buff *skb, struct netlink_callback *cb) 
	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 @@ static int packet_diag_dump(struct sk_buff *skb, struct netlink_callback *cb) 
		num++;

	}

done:

	rcu_read_unlock();

	mutex_unlock(&net->packet.sklist_lock);

	cb->args[0] = num;



	return skb->len;