INFO: task hung in ovs_exit_net

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a6c0d093 net: explicitly include <linux/compat.h> in net/c..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=179ee640900000
kernel config: https://syzkaller.appspot.com/x/.config?x=2b7b67c0c1819c87
dashboard link: https://syzkaller.appspot.com/bug?extid=2c4ff3614695f75ce26c
compiler: gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2c4ff3...@syzkaller.appspotmail.com

INFO: task kworker/u4:3:235 blocked for more than 143 seconds.
Not tainted 5.8.0-rc4-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:3 D24856 235 2 0x00004000
Workqueue: netns cleanup_net
Call Trace:
context_switch kernel/sched/core.c:3453 [inline]
__schedule+0x8e1/0x1eb0 kernel/sched/core.c:4178
schedule+0xd0/0x2a0 kernel/sched/core.c:4253
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:4312
__mutex_lock_common kernel/locking/mutex.c:1033 [inline]
__mutex_lock+0x3e2/0x10d0 kernel/locking/mutex.c:1103
ovs_lock net/openvswitch/datapath.c:105 [inline]
ovs_exit_net+0x1de/0xba0 net/openvswitch/datapath.c:2491
ops_exit_list+0xb0/0x160 net/core/net_namespace.c:186
cleanup_net+0x4ea/0xa00 net/core/net_namespace.c:603
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:291
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
INFO: task kworker/0:5:9052 blocked for more than 143 seconds.
Not tainted 5.8.0-rc4-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/0:5 D27408 9052 2 0x00004000
Workqueue: events ovs_dp_masks_rebalance
Call Trace:
context_switch kernel/sched/core.c:3453 [inline]
__schedule+0x8e1/0x1eb0 kernel/sched/core.c:4178
schedule+0xd0/0x2a0 kernel/sched/core.c:4253
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:4312
__mutex_lock_common kernel/locking/mutex.c:1033 [inline]
__mutex_lock+0x3e2/0x10d0 kernel/locking/mutex.c:1103
ovs_lock net/openvswitch/datapath.c:105 [inline]
ovs_dp_masks_rebalance+0x18/0x80 net/openvswitch/datapath.c:2355
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:291
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
INFO: task syz-executor.3:21286 blocked for more than 143 seconds.
Not tainted 5.8.0-rc4-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D26160 21286 7072 0x00004004
Call Trace:
context_switch kernel/sched/core.c:3453 [inline]
__schedule+0x8e1/0x1eb0 kernel/sched/core.c:4178
schedule+0xd0/0x2a0 kernel/sched/core.c:4253
schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1873
do_wait_for_common kernel/sched/completion.c:85 [inline]
__wait_for_common kernel/sched/completion.c:106 [inline]
wait_for_common kernel/sched/completion.c:117 [inline]
wait_for_completion+0x163/0x260 kernel/sched/completion.c:138
__flush_work+0x51f/0xab0 kernel/workqueue.c:3046
__cancel_work_timer+0x5de/0x700 kernel/workqueue.c:3133
ovs_dp_cmd_del+0x18c/0x270 net/openvswitch/datapath.c:1790
genl_family_rcv_msg_doit net/netlink/genetlink.c:669 [inline]
genl_family_rcv_msg net/netlink/genetlink.c:714 [inline]
genl_rcv_msg+0x61d/0x980 net/netlink/genetlink.c:731
netlink_rcv_skb+0x15a/0x430 net/netlink/af_netlink.c:2470
genl_rcv+0x24/0x40 net/netlink/genetlink.c:742
netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
sock_sendmsg_nosec net/socket.c:651 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:671
____sys_sendmsg+0x6e8/0x810 net/socket.c:2363
___sys_sendmsg+0xf3/0x170 net/socket.c:2417
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2450
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45c1f9
Code: Bad RIP value.
RSP: 002b:00007f75a409cc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000002b3c0 RCX: 000000000045c1f9
RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000000000004
RBP: 000000000078bf40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078bf0c
R13: 00007ffed0e2724f R14: 00007f75a409d9c0 R15: 000000000078bf0c
INFO: task syz-executor.3:21355 blocked for more than 144 seconds.
Not tainted 5.8.0-rc4-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D27400 21355 7072 0x00004004
Call Trace:
context_switch kernel/sched/core.c:3453 [inline]
__schedule+0x8e1/0x1eb0 kernel/sched/core.c:4178
schedule+0xd0/0x2a0 kernel/sched/core.c:4253
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:4312
__mutex_lock_common kernel/locking/mutex.c:1033 [inline]
__mutex_lock+0x3e2/0x10d0 kernel/locking/mutex.c:1103
ovs_lock net/openvswitch/datapath.c:105 [inline]
ovs_dp_cmd_del+0x4a/0x270 net/openvswitch/datapath.c:1780
genl_family_rcv_msg_doit net/netlink/genetlink.c:669 [inline]
genl_family_rcv_msg net/netlink/genetlink.c:714 [inline]
genl_rcv_msg+0x61d/0x980 net/netlink/genetlink.c:731
netlink_rcv_skb+0x15a/0x430 net/netlink/af_netlink.c:2470
genl_rcv+0x24/0x40 net/netlink/genetlink.c:742
netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
sock_sendmsg_nosec net/socket.c:651 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:671
____sys_sendmsg+0x6e8/0x810 net/socket.c:2363
___sys_sendmsg+0xf3/0x170 net/socket.c:2417
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2450
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45c1f9
Code: Bad RIP value.
RSP: 002b:00007f75a405ac78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000002b3c0 RCX: 000000000045c1f9
RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000000000004
RBP: 000000000078c080 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078c04c
R13: 00007ffed0e2724f R14: 00007f75a405b9c0 R15: 000000000078c04c

Showing all locks held in the system:
4 locks held by kworker/u4:3/235:
#0: ffff8880a97ad138 ((wq_completion)netns){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: ffff8880a97ad138 ((wq_completion)netns){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
#0: ffff8880a97ad138 ((wq_completion)netns){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
#0: ffff8880a97ad138 ((wq_completion)netns){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
#0: ffff8880a97ad138 ((wq_completion)netns){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
#0: ffff8880a97ad138 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x82b/0x1670 kernel/workqueue.c:2240
#1: ffffc90001847da8 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x85f/0x1670 kernel/workqueue.c:2244
#2: ffffffff8a7ad4b0 (pernet_ops_rwsem){++++}-{3:3}, at: cleanup_net+0x9b/0xa00 net/core/net_namespace.c:565
#3: ffffffff8aa5dfe8 (ovs_mutex){+.+.}-{3:3}, at: ovs_lock net/openvswitch/datapath.c:105 [inline]
#3: ffffffff8aa5dfe8 (ovs_mutex){+.+.}-{3:3}, at: ovs_exit_net+0x1de/0xba0 net/openvswitch/datapath.c:2491
1 lock held by khungtaskd/1150:
#0: ffffffff89bc0ec0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:5779
1 lock held by in:imklog/6505:
3 locks held by kworker/0:5/9052:
#0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
#0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
#0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
#0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
#0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x82b/0x1670 kernel/workqueue.c:2240
#1: ffffc90001b17da8 ((work_completion)(&(&dp->masks_rebalance)->work)){+.+.}-{0:0}, at: process_one_work+0x85f/0x1670 kernel/workqueue.c:2244
#2: ffffffff8aa5dfe8 (ovs_mutex){+.+.}-{3:3}, at: ovs_lock net/openvswitch/datapath.c:105 [inline]
#2: ffffffff8aa5dfe8 (ovs_mutex){+.+.}-{3:3}, at: ovs_dp_masks_rebalance+0x18/0x80 net/openvswitch/datapath.c:2355
2 locks held by syz-executor.3/21286:
#0: ffffffff8a817cf0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40 net/netlink/genetlink.c:741
#1: ffffffff8aa5dfe8 (ovs_mutex){+.+.}-{3:3}, at: ovs_lock net/openvswitch/datapath.c:105 [inline]
#1: ffffffff8aa5dfe8 (ovs_mutex){+.+.}-{3:3}, at: ovs_dp_cmd_del+0x4a/0x270 net/openvswitch/datapath.c:1780
2 locks held by syz-executor.3/21355:
#0: ffffffff8a817cf0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40 net/netlink/genetlink.c:741
#1: ffffffff8aa5dfe8 (ovs_mutex){+.+.}-{3:3}, at: ovs_lock net/openvswitch/datapath.c:105 [inline]
#1: ffffffff8aa5dfe8 (ovs_mutex){+.+.}-{3:3}, at: ovs_dp_cmd_del+0x4a/0x270 net/openvswitch/datapath.c:1780

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 1150 Comm: khungtaskd Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x18f/0x20d lib/dump_stack.c:118
nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1b3/0x223 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:209 [inline]
watchdog+0xd7d/0x1000 kernel/hung_task.c:295
kthread+0x3b5/0x4a0 kernel/kthread.c:291
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:60


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[Eelco Chaudron]

Looks like the same problem as “[ovs-dev] INFO: task hung in
ovs_dp_masks_rebalance”.

//Eelco

> _______________________________________________
> dev mailing list
> d...@openvswitch.org
> https://mail.openvswitch.org/mailman/listinfo/ovs-dev

[Hillf Danton]

Wed, 22 Jul 2020 23:27:19 -0700

Fixes: eac87c413bf9 ("net: openvswitch: reorder masks array based on usage")
by moving cancel_delayed_work_sync() in to the rcu cb, therefore out of ovs
lock. To facilitate that, add a flag in datapath to inform the kworker that
there is no more work needed.


--- a/net/openvswitch/datapath.h
+++ b/net/openvswitch/datapath.h
@@ -82,6 +82,7 @@ struct datapath {

u32 max_headroom;

+ int called_rcu;
/* Switch meters. */
struct dp_meter_table meter_tbl;

--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -161,6 +161,7 @@ static void destroy_dp_rcu(struct rcu_he
{
struct datapath *dp = container_of(rcu, struct datapath, rcu);

+ cancel_delayed_work_sync(&dp->masks_rebalance);
ovs_flow_tbl_destroy(&dp->table);
free_percpu(dp->stats_percpu);
kfree(dp->ports);
@@ -1760,11 +1761,9 @@ static void __dp_destroy(struct datapath
*/
ovs_dp_detach_port(ovs_vport_ovsl(dp, OVSP_LOCAL));

+ dp->called_rcu = true;
/* RCU destroy the flow table */
call_rcu(&dp->rcu, destroy_dp_rcu);
-
- /* Cancel remaining work. */
- cancel_delayed_work_sync(&dp->masks_rebalance);
}

static int ovs_dp_cmd_del(struct sk_buff *skb, struct genl_info *info)
@@ -2356,6 +2355,8 @@ static void ovs_dp_masks_rebalance(struc
ovs_flow_masks_rebalance(&dp->table);
ovs_unlock();

+ if (dp->called_rcu)
+ return;
schedule_delayed_work(&dp->masks_rebalance,
msecs_to_jiffies(DP_MASKS_REBALANCE_INTERVAL));
}

[Eelco Chaudron]

On 23 Jul 2020, at 13:06, Hillf Danton wrote:

> Wed, 22 Jul 2020 23:27:19 -0700
>> syzbot found the following issue on:

<SNIP>

>
> Fixes: eac87c413bf9 ("net: openvswitch: reorder masks array based on
> usage")
> by moving cancel_delayed_work_sync() in to the rcu cb, therefore out
> of ovs
> lock. To facilitate that, add a flag in datapath to inform the kworker
> that
> there is no more work needed.

I was thinking of re-working the patch and move the handling to the
“struct ovs_net” instead of the datapath. This way the rebalance
worker can rebalance all datapaths in the netns. Than I can move
cancel_delayed_work_sync() from __dp_destroy()
to ovs_exit_net(), i.e. outside the ovs lock scope.

However, your fix would be way less intrusive. Are you planning on
sending it as a patch? If so, maybe add a comment around the called_rcu
variable to be more clear where it’s used for, or maybe rename it to
something like called_destory_rcu?

If you think my approach would be better let me know, and I work on a
patch.

Feedback anyone?

[Hillf Danton]

On Thu, 23 Jul 2020 13:48:59 +0200 Eelco Chaudron wrote:
> On 23 Jul 2020, at 13:06, Hillf Danton wrote:
>
> > Wed, 22 Jul 2020 23:27:19 -0700
> >> syzbot found the following issue on:
> <SNIP>
> >
> > Fixes: eac87c413bf9 ("net: openvswitch: reorder masks array based on usage")
> > by moving cancel_delayed_work_sync() in to the rcu cb, therefore out of ovs
> > lock. To facilitate that, add a flag in datapath to inform the kworker that
> > there is no more work needed.
>
> I was thinking of re-working the patch and move the handling to the
> “struct ovs_net” instead of the datapath. This way the rebalance
> worker can rebalance all datapaths in the netns. Than I can move
> cancel_delayed_work_sync() from __dp_destroy()
> to ovs_exit_net(), i.e. outside the ovs lock scope.

I have no prefer over either way.

> However, your fix would be way less intrusive. Are you planning on
> sending it as a patch?

This is the candy to get syzbot out of depression and frustration and
work again tomorrow.

> If so, maybe add a comment around the called_rcu
> variable to be more clear where it’s used for, or maybe rename it to
> something like called_destory_rcu?

I try much to avoid over-comment, see below, given the absence of
something like is_rcu_called(rcu);

> If you think my approach would be better let me know, and I work on a
> patch.

Feel free to do what you like.