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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:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.