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Date: Wed, 11 Jan 2012 15:56:52 +0100
From: Eric Dumazet <eric.dumazet@...il.com>
To: Hans Schillstrom <hans.schillstrom@...csson.com>
Cc: "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
netdev <netdev@...r.kernel.org>
Subject: Re: conntrack, suspicious RCU usage
Le mercredi 11 janvier 2012 à 14:33 +0100, Eric Dumazet a écrit :
> Le mercredi 11 janvier 2012 à 14:24 +0100, Hans Schillstrom a écrit :
> > On Wednesday 11 January 2012 11:01:51 Eric Dumazet wrote:
>
> > > Hmm, we either need to take rcu_read_lock() while calling
> > > __nf_ct_l3proto_find(), or define a variant using
> > > rcu_dereference_protected() in places we hold nf_conntrack_lock
> > >
> > I made a qick test with locks /unlocks in
> > __nf_ct_l3proto_find() and __nf_ct_l4proto_find()
> >
> > rcu_read_lock();
> > ...
> > rcu_read_unlock();
> > return retp;
> >
> > It seems to help, I cant see the dump anymore and everything else that I run works ...
> >
> >
>
> You cant do that, its just a brown paper bag :)
>
> If "retp" is returned, then the caller must handle the rcu_read_unlock()
> itself, after all possible "retp" dereferences.
>
> But really adding rcu_read_lock() should not be necessary on paths we
> own the conntrack lock. We should use rcu_dereference_protected()
> instead.
>
Well, __nf_ct_l4proto_find() being out of line and the way we already
use rcu_read_lock() in this code, it seems following patch is
the most natural way to cope with these lockdep warnings.
Thanks
[PATCH] netfilter: ctnetlink: fix lockep splats
net/netfilter/nf_conntrack_proto.c:70 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 1, debug_locks = 0
3 locks held by conntrack/3235:
#0: (nfnl_mutex){+.+.+.}, at: [<ffffffff81603537>]
nfnl_lock+0x17/0x20
#1: (nlk->cb_mutex){+.+.+.}, at: [<ffffffff815fbd72>]
netlink_dump+0x32/0x240
#2: (nf_conntrack_lock){+.-...}, at: [<ffffffffa0115d2e>]
ctnetlink_dump_table+0x3e/0x170 [nf_conntrack_netlink]
stack backtrace:
Pid: 3235, comm: conntrack Tainted: G W 3.2.0+ #511
Call Trace:
[<ffffffff8108ce45>] lockdep_rcu_suspicious+0xe5/0x100
[<ffffffffa00ec6e1>] __nf_ct_l4proto_find+0x81/0xb0 [nf_conntrack]
[<ffffffffa0115675>] ctnetlink_fill_info+0x215/0x5f0 [nf_conntrack_netlink]
[<ffffffffa0115dc1>] ctnetlink_dump_table+0xd1/0x170 [nf_conntrack_netlink]
[<ffffffff815fbdbf>] netlink_dump+0x7f/0x240
[<ffffffff81090f9d>] ? trace_hardirqs_on+0xd/0x10
[<ffffffff815fd34f>] netlink_dump_start+0xdf/0x190
[<ffffffffa0111490>] ? ctnetlink_change_nat_seq_adj+0x160/0x160 [nf_conntrack_netlink]
[<ffffffffa0115cf0>] ? ctnetlink_get_conntrack+0x2a0/0x2a0 [nf_conntrack_netlink]
[<ffffffffa0115ad9>] ctnetlink_get_conntrack+0x89/0x2a0 [nf_conntrack_netlink]
[<ffffffff81603a47>] nfnetlink_rcv_msg+0x467/0x5f0
[<ffffffff81603a7c>] ? nfnetlink_rcv_msg+0x49c/0x5f0
[<ffffffff81603922>] ? nfnetlink_rcv_msg+0x342/0x5f0
[<ffffffff81071b21>] ? get_parent_ip+0x11/0x50
[<ffffffff816035e0>] ? nfnetlink_subsys_register+0x60/0x60
[<ffffffff815fed49>] netlink_rcv_skb+0xa9/0xd0
[<ffffffff81603475>] nfnetlink_rcv+0x15/0x20
[<ffffffff815fe70e>] netlink_unicast+0x1ae/0x1f0
[<ffffffff815fea16>] netlink_sendmsg+0x2c6/0x320
[<ffffffff815b2a87>] sock_sendmsg+0x117/0x130
[<ffffffff81125093>] ? might_fault+0x53/0xb0
[<ffffffff811250dc>] ? might_fault+0x9c/0xb0
[<ffffffff81125093>] ? might_fault+0x53/0xb0
[<ffffffff815b5991>] ? move_addr_to_kernel+0x71/0x80
[<ffffffff815b644e>] sys_sendto+0xfe/0x130
[<ffffffff815b5c94>] ? sys_bind+0xb4/0xd0
[<ffffffff817a8a0e>] ? retint_swapgs+0xe/0x13
[<ffffffff817afcd2>] system_call_fastpath+0x16/0x1b
Reported-by: Hans Schillstrom <hans.schillstrom@...csson.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
net/netfilter/nf_conntrack_netlink.c | 31 ++++++++++++++-----------
1 file changed, 18 insertions(+), 13 deletions(-)
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index e07dc3a..14840d9 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -110,15 +110,15 @@ ctnetlink_dump_tuples(struct sk_buff *skb,
struct nf_conntrack_l3proto *l3proto;
struct nf_conntrack_l4proto *l4proto;
+ rcu_read_lock();
l3proto = __nf_ct_l3proto_find(tuple->src.l3num);
ret = ctnetlink_dump_tuples_ip(skb, tuple, l3proto);
- if (unlikely(ret < 0))
- return ret;
-
- l4proto = __nf_ct_l4proto_find(tuple->src.l3num, tuple->dst.protonum);
- ret = ctnetlink_dump_tuples_proto(skb, tuple, l4proto);
-
+ if (ret >= 0) {
+ l4proto = __nf_ct_l4proto_find(tuple->src.l3num, tuple->dst.protonum);
+ ret = ctnetlink_dump_tuples_proto(skb, tuple, l4proto);
+ }
+ rcu_read_unlock();
return ret;
}
@@ -703,6 +703,7 @@ ctnetlink_dump_table(struct sk_buff *skb, struct netlink_callback *cb)
struct hlist_nulls_node *n;
struct nfgenmsg *nfmsg = nlmsg_data(cb->nlh);
u_int8_t l3proto = nfmsg->nfgen_family;
+ int res;
spin_lock_bh(&nf_conntrack_lock);
last = (struct nf_conn *)cb->args[1];
@@ -723,11 +724,14 @@ restart:
continue;
cb->args[1] = 0;
}
- if (ctnetlink_fill_info(skb, NETLINK_CB(cb->skb).pid,
+ rcu_read_lock();
+ res = ctnetlink_fill_info(skb, NETLINK_CB(cb->skb).pid,
cb->nlh->nlmsg_seq,
NFNL_MSG_TYPE(
cb->nlh->nlmsg_type),
- ct) < 0) {
+ ct);
+ rcu_read_unlock();
+ if (res < 0) {
nf_conntrack_get(&ct->ct_general);
cb->args[1] = (unsigned long)ct;
goto out;
@@ -1626,17 +1630,18 @@ ctnetlink_exp_dump_mask(struct sk_buff *skb,
if (!nest_parms)
goto nla_put_failure;
+ rcu_read_lock();
l3proto = __nf_ct_l3proto_find(tuple->src.l3num);
ret = ctnetlink_dump_tuples_ip(skb, &m, l3proto);
+ if (ret >= 0) {
+ l4proto = __nf_ct_l4proto_find(tuple->src.l3num, tuple->dst.protonum);
+ ret = ctnetlink_dump_tuples_proto(skb, &m, l4proto);
+ }
+ rcu_read_unlock();
if (unlikely(ret < 0))
goto nla_put_failure;
- l4proto = __nf_ct_l4proto_find(tuple->src.l3num, tuple->dst.protonum);
- ret = ctnetlink_dump_tuples_proto(skb, &m, l4proto);
- if (unlikely(ret < 0))
- goto nla_put_failure;
-
nla_nest_end(skb, nest_parms);
return 0;
--
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