[PATCH 5.15 108/123] tipc: call tipc_lxc_xmit without holding node_read_lock

Greg Kroah-Hartman
2022-12-12T13:33:04Z

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit 88956177db179e4eba7cd590971961857d1565b8 ]

When sending packets between nodes in netns, it calls tipc_lxc_xmit() for
peer node to receive the packets where tipc_sk_mcast_rcv()/tipc_sk_rcv()
might be called, and it's pretty much like in tipc_rcv().

Currently the local 'node rw lock' is held during calling tipc_lxc_xmit()
to protect the peer_net not being freed by another thread. However, when
receiving these packets, tipc_node_add_conn() might be called where the
peer 'node rw lock' is acquired. Then a dead lock warning is triggered by
lockdep detector, although it is not a real dead lock:

WARNING: possible recursive locking detected
--------------------------------------------
conn_server/1086 is trying to acquire lock:
ffff8880065cb020 (&n->lock#2){++--}-{2:2}, \
at: tipc_node_add_conn.cold.76+0xaa/0x211 [tipc]

but task is already holding lock:
ffff8880065cd020 (&n->lock#2){++--}-{2:2}, \
at: tipc_node_xmit+0x285/0xb30 [tipc]

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&n->lock#2);
lock(&n->lock#2);

*** DEADLOCK ***

May be due to missing lock nesting notation

4 locks held by conn_server/1086:
#0: ffff8880036d1e40 (sk_lock-AF_TIPC){+.+.}-{0:0}, \
at: tipc_accept+0x9c0/0x10b0 [tipc]
#1: ffff8880036d5f80 (sk_lock-AF_TIPC/1){+.+.}-{0:0}, \
at: tipc_accept+0x363/0x10b0 [tipc]
#2: ffff8880065cd020 (&n->lock#2){++--}-{2:2}, \
at: tipc_node_xmit+0x285/0xb30 [tipc]
#3: ffff888012e13370 (slock-AF_TIPC){+...}-{2:2}, \
at: tipc_sk_rcv+0x2da/0x1b40 [tipc]

Call Trace:
<TASK>
dump_stack_lvl+0x44/0x5b
__lock_acquire.cold.77+0x1f2/0x3d7
lock_acquire+0x1d2/0x610
_raw_write_lock_bh+0x38/0x80
tipc_node_add_conn.cold.76+0xaa/0x211 [tipc]
tipc_sk_finish_conn+0x21e/0x640 [tipc]
tipc_sk_filter_rcv+0x147b/0x3030 [tipc]
tipc_sk_rcv+0xbb4/0x1b40 [tipc]
tipc_lxc_xmit+0x225/0x26b [tipc]
tipc_node_xmit.cold.82+0x4a/0x102 [tipc]
__tipc_sendstream+0x879/0xff0 [tipc]
tipc_accept+0x966/0x10b0 [tipc]
do_accept+0x37d/0x590

This patch avoids this warning by not holding the 'node rw lock' before
calling tipc_lxc_xmit(). As to protect the 'peer_net', rcu_read_lock()
should be enough, as in cleanup_net() when freeing the netns, it calls
synchronize_rcu() before the free is continued.

Also since tipc_lxc_xmit() is like the RX path in tipc_rcv(), it makes
sense to call it under rcu_read_lock(). Note that the right lock order
must be:

rcu_read_lock();
tipc_node_read_lock(n);
tipc_node_read_unlock(n);
tipc_lxc_xmit();
rcu_read_unlock();

instead of:

tipc_node_read_lock(n);
rcu_read_lock();
tipc_node_read_unlock(n);
tipc_lxc_xmit();
rcu_read_unlock();

and we have to call tipc_node_read_lock/unlock() twice in
tipc_node_xmit().

Fixes: f73b12812a3d ("tipc: improve throughput between nodes in netns")
Reported-by: Shuang Li <shuali@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://lore.kernel.org/r/5bdd1f8fee9db695cfff4528a48c9b9d0523fb00.1670110641.git.lucien.xin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/tipc/node.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/tipc/node.c b/net/tipc/node.c
index b48d97cbbe29..49ddc484c4fe 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -1689,6 +1689,7 @@ int tipc_node_xmit(struct net *net, struct sk_buff_head *list,
struct tipc_node *n;
struct sk_buff_head xmitq;
bool node_up = false;
+ struct net *peer_net;
int bearer_id;
int rc;

@@ -1705,18 +1706,23 @@ int tipc_node_xmit(struct net *net, struct sk_buff_head *list,
return -EHOSTUNREACH;
}

+ rcu_read_lock();
tipc_node_read_lock(n);
node_up = node_is_up(n);
- if (node_up && n->peer_net && check_net(n->peer_net)) {
+ peer_net = n->peer_net;
+ tipc_node_read_unlock(n);
+ if (node_up && peer_net && check_net(peer_net)) {
/* xmit inner linux container */
- tipc_lxc_xmit(n->peer_net, list);
+ tipc_lxc_xmit(peer_net, list);
if (likely(skb_queue_empty(list))) {
- tipc_node_read_unlock(n);
+ rcu_read_unlock();
tipc_node_put(n);
return 0;
}
}
+ rcu_read_unlock();

+ tipc_node_read_lock(n);
bearer_id = n->active_links[selector & 1];
if (unlikely(bearer_id == INVALID_BEARER_ID)) {
tipc_node_read_unlock(n);
--
2.35.1