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While destroying a network namespace that contains a L2TP tunnel a
"BUG: scheduling while atomic" can be observed.
Enabling lockdep shows that this is happening because l2tp_exit_net()
is calling l2tp_tunnel_closeall() (via l2tp_tunnel_delete()) from
within an RCU critical section.
l2tp_exit_net() takes rcu_read_lock_bh()
<< list_for_each_entry_rcu() >>
l2tp_tunnel_delete()
l2tp_tunnel_closeall()
__l2tp_session_unhash()
synchronize_rcu() << Illegal inside RCU critical section >>
BUG: sleeping function called from invalid context
in_atomic(): 1, irqs_disabled(): 0, pid: 86, name: kworker/u16:2
INFO: lockdep is turned off.
CPU: 2 PID: 86 Comm: kworker/u16:2 Tainted: G W O 4.4.6-at1 #2
Hardware name: Xen HVM domU, BIOS 4.6.1-xs125300 05/09/2016
Workqueue: netns cleanup_net
0000000000000000 ffff880202417b90 ffffffff812b0013 ffff880202410ac0
ffffffff81870de8 ffff880202417bb8 ffffffff8107aee8 ffffffff81870de8
0000000000000c51 0000000000000000 ffff880202417be0 ffffffff8107b024
Call Trace:
[<ffffffff812b0013>] dump_stack+0x85/0xc2
[<ffffffff8107aee8>] ___might_sleep+0x148/0x240
[<ffffffff8107b024>] __might_sleep+0x44/0x80
[<ffffffff810b21bd>] synchronize_sched+0x2d/0xe0
[<ffffffff8109be6d>] ? trace_hardirqs_on+0xd/0x10
[<ffffffff8105c7bb>] ? __local_bh_enable_ip+0x6b/0xc0
[<ffffffff816a1b00>] ? _raw_spin_unlock_bh+0x30/0x40
[<ffffffff81667482>] __l2tp_session_unhash+0x172/0x220
[<ffffffff81667397>] ? __l2tp_session_unhash+0x87/0x220
[<ffffffff8166888b>] l2tp_tunnel_closeall+0x9b/0x140
[<ffffffff81668c74>] l2tp_tunnel_delete+0x14/0x60
[<ffffffff81668dd0>] l2tp_exit_net+0x110/0x270
[<ffffffff81668d5c>] ? l2tp_exit_net+0x9c/0x270
[<ffffffff815001c3>] ops_exit_list.isra.6+0x33/0x60
[<ffffffff81501166>] cleanup_net+0x1b6/0x280
...
This bug can easily be reproduced with a few steps:
$ sudo unshare -n bash # Create a shell in a new namespace
# ip link set lo up
# ip addr add 127.0.0.1 dev lo
# ip l2tp add tunnel remote 127.0.0.1 local 127.0.0.1 tunnel_id 1 \
peer_tunnel_id 1 udp_sport 50000 udp_dport 50000
# ip l2tp add session name foo tunnel_id 1 session_id 1 \
peer_session_id 1
# ip link set foo up
# exit # Exit the shell, in turn exiting the namespace
$ dmesg
...
[942121.089216] BUG: scheduling while atomic: kworker/u16:3/13872/0x00000200
...
To fix this, move the call to l2tp_tunnel_closeall() out of the RCU
critical section, and instead call it from l2tp_tunnel_del_work(), which
is running from the l2tp_wq workqueue.
Fixes:
|
||
|---|---|---|
| .. | ||
| 6lowpan | ||
| 9p | ||
| 802 | ||
| 8021q | ||
| appletalk | ||
| atm | ||
| ax25 | ||
| batman-adv | ||
| bluetooth | ||
| bridge | ||
| caif | ||
| can | ||
| ceph | ||
| core | ||
| dcb | ||
| dccp | ||
| decnet | ||
| dns_resolver | ||
| dsa | ||
| ethernet | ||
| hsr | ||
| ieee802154 | ||
| ife | ||
| ipv4 | ||
| ipv6 | ||
| ipx | ||
| irda | ||
| iucv | ||
| kcm | ||
| key | ||
| l2tp | ||
| l3mdev | ||
| lapb | ||
| llc | ||
| mac80211 | ||
| mac802154 | ||
| mpls | ||
| ncsi | ||
| netfilter | ||
| netlabel | ||
| netlink | ||
| netrom | ||
| nfc | ||
| openvswitch | ||
| packet | ||
| phonet | ||
| psample | ||
| qrtr | ||
| rds | ||
| rfkill | ||
| rose | ||
| rxrpc | ||
| sched | ||
| sctp | ||
| smc | ||
| strparser | ||
| sunrpc | ||
| switchdev | ||
| tipc | ||
| unix | ||
| vmw_vsock | ||
| wimax | ||
| wireless | ||
| x25 | ||
| xfrm | ||
| compat.c | ||
| Kconfig | ||
| Makefile | ||
| socket.c | ||
| sysctl_net.c | ||