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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: f73b12812a ("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>
88956177db