Re: possible deadlock in process_one_work

From: Dmitry Vyukov
Date: Tue Oct 31 2017 - 09:22:32 EST

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Another one:

WARNING: possible circular locking dependency detected
4.13.0-rc6-next-20170825+ #9 Not tainted
------------------------------------------------------
syz-executor0/3387 is trying to acquire lock:
(cpu_hotplug_lock.rw_sem){++++}, at: [<ffffffff8185325d>]
static_key_slow_inc+0x9d/0x3c0 kernel/jump_label.c:123

but task is already holding lock:
(rtnl_mutex){+.+.}, at: [<ffffffff83ed8cfc>] rtnl_lock
net/core/rtnetlink.c:72 [inline]
(rtnl_mutex){+.+.}, at: [<ffffffff83ed8cfc>]
rtnetlink_rcv_msg+0x65c/0x1090 net/core/rtnetlink.c:4241

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (rtnl_mutex){+.+.}:
check_prevs_add kernel/locking/lockdep.c:2020 [inline]
validate_chain kernel/locking/lockdep.c:2469 [inline]
__lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0x16f/0x1870 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
rtnl_lock+0x17/0x20 net/core/rtnetlink.c:72
reg_todo+0xc6/0xbe0 net/wireless/reg.c:2337
process_one_work+0xbfd/0x1be0 kernel/workqueue.c:2098
worker_thread+0x223/0x1860 kernel/workqueue.c:2233
kthread+0x39c/0x470 kernel/kthread.c:231
ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431

-> #2 (reg_work){+.+.}:
process_one_work+0xba5/0x1be0 kernel/workqueue.c:2095
worker_thread+0x223/0x1860 kernel/workqueue.c:2233
kthread+0x39c/0x470 kernel/kthread.c:231
ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
0xffffffffffffffff

-> #1 ((complete)&rcu.completion){+.+.}:
check_prevs_add kernel/locking/lockdep.c:2020 [inline]
validate_chain kernel/locking/lockdep.c:2469 [inline]
__lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
complete_acquire include/linux/completion.h:39 [inline]
__wait_for_common kernel/sched/completion.c:108 [inline]
wait_for_common kernel/sched/completion.c:122 [inline]
wait_for_completion+0xc8/0x770 kernel/sched/completion.c:143
__synchronize_srcu+0x1b5/0x250 kernel/rcu/srcutree.c:898
synchronize_srcu_expedited kernel/rcu/srcutree.c:923 [inline]
synchronize_srcu+0x1a3/0x560 kernel/rcu/srcutree.c:974
quarantine_remove_cache+0xd7/0xf0 mm/kasan/quarantine.c:327
kasan_cache_shrink+0x9/0x10 mm/kasan/kasan.c:380
kmem_cache_shrink+0x15/0x30 mm/slab_common.c:857
acpi_os_purge_cache+0x15/0x20 drivers/acpi/osl.c:1560
acpi_purge_cached_objects+0x38/0xc9 drivers/acpi/acpica/utxface.c:271
acpi_initialize_objects+0xc5/0x112 drivers/acpi/acpica/utxfinit.c:302
acpi_bus_init drivers/acpi/bus.c:1131 [inline]
acpi_init+0x23c/0x8e6 drivers/acpi/bus.c:1220
do_one_initcall+0x9e/0x330 init/main.c:826
do_initcall_level init/main.c:892 [inline]
do_initcalls init/main.c:900 [inline]
do_basic_setup init/main.c:918 [inline]
kernel_init_freeable+0x469/0x521 init/main.c:1066
kernel_init+0x13/0x172 init/main.c:993
ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431

-> #0 (cpu_hotplug_lock.rw_sem){++++}:
check_prev_add+0x865/0x1520 kernel/locking/lockdep.c:1894
check_prevs_add kernel/locking/lockdep.c:2020 [inline]
validate_chain kernel/locking/lockdep.c:2469 [inline]
__lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:35 [inline]
percpu_down_read include/linux/percpu-rwsem.h:58 [inline]
cpus_read_lock+0x42/0x90 kernel/cpu.c:218
static_key_slow_inc+0x9d/0x3c0 kernel/jump_label.c:123
ip_tunnel_need_metadata+0x15/0x20 net/ipv4/ip_tunnel_core.c:431
fib_nl_newrule+0x192f/0x2b80 net/core/fib_rules.c:610
rtnetlink_rcv_msg+0x733/0x1090 net/core/rtnetlink.c:4246
netlink_rcv_skb+0x216/0x440 net/netlink/af_netlink.c:2397
rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4258
netlink_unicast_kernel net/netlink/af_netlink.c:1265 [inline]
netlink_unicast+0x4e8/0x6f0 net/netlink/af_netlink.c:1291
netlink_sendmsg+0xa4a/0xe70 net/netlink/af_netlink.c:1854
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:643
sock_write_iter+0x320/0x5e0 net/socket.c:912
call_write_iter include/linux/fs.h:1744 [inline]
do_iter_readv_writev+0x531/0x7f0 fs/read_write.c:650
do_iter_write+0x15a/0x540 fs/read_write.c:929
vfs_writev+0x18a/0x340 fs/read_write.c:975
do_writev+0xfc/0x2a0 fs/read_write.c:1011
SYSC_writev fs/read_write.c:1084 [inline]
SyS_writev+0x27/0x30 fs/read_write.c:1081
entry_SYSCALL_64_fastpath+0x1f/0xbe

other info that might help us debug this:

Chain exists of:
cpu_hotplug_lock.rw_sem --> reg_work --> rtnl_mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(rtnl_mutex);
lock(reg_work);
lock(rtnl_mutex);
lock(cpu_hotplug_lock.rw_sem);

*** DEADLOCK ***

1 lock held by syz-executor0/3387:
#0: (rtnl_mutex){+.+.}, at: [<ffffffff83ed8cfc>] rtnl_lock
net/core/rtnetlink.c:72 [inline]
#0: (rtnl_mutex){+.+.}, at: [<ffffffff83ed8cfc>]
rtnetlink_rcv_msg+0x65c/0x1090 net/core/rtnetlink.c:4241

stack backtrace:
CPU: 3 PID: 3387 Comm: syz-executor0 Not tainted 4.13.0-rc6-next-20170825+ #9
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16 [inline]
dump_stack+0x194/0x257 lib/dump_stack.c:52
print_circular_bug+0x503/0x710 kernel/locking/lockdep.c:1259
check_prev_add+0x865/0x1520 kernel/locking/lockdep.c:1894
check_prevs_add kernel/locking/lockdep.c:2020 [inline]
validate_chain kernel/locking/lockdep.c:2469 [inline]
__lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:35 [inline]
percpu_down_read include/linux/percpu-rwsem.h:58 [inline]
cpus_read_lock+0x42/0x90 kernel/cpu.c:218
static_key_slow_inc+0x9d/0x3c0 kernel/jump_label.c:123
ip_tunnel_need_metadata+0x15/0x20 net/ipv4/ip_tunnel_core.c:431
fib_nl_newrule+0x192f/0x2b80 net/core/fib_rules.c:610
rtnetlink_rcv_msg+0x733/0x1090 net/core/rtnetlink.c:4246
netlink_rcv_skb+0x216/0x440 net/netlink/af_netlink.c:2397
rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4258
netlink_unicast_kernel net/netlink/af_netlink.c:1265 [inline]
netlink_unicast+0x4e8/0x6f0 net/netlink/af_netlink.c:1291
netlink_sendmsg+0xa4a/0xe70 net/netlink/af_netlink.c:1854
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:643
sock_write_iter+0x320/0x5e0 net/socket.c:912
call_write_iter include/linux/fs.h:1744 [inline]
do_iter_readv_writev+0x531/0x7f0 fs/read_write.c:650
do_iter_write+0x15a/0x540 fs/read_write.c:929
vfs_writev+0x18a/0x340 fs/read_write.c:975
do_writev+0xfc/0x2a0 fs/read_write.c:1011
SYSC_writev fs/read_write.c:1084 [inline]
SyS_writev+0x27/0x30 fs/read_write.c:1081
entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x446749
RSP: 002b:00007f0b16357c08 EFLAGS: 00000292 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000446749
RDX: 0000000000000001 RSI: 0000000020917ff0 RDI: 0000000000000005
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000292 R12: 0000000000000000

On Tue, Oct 31, 2017 at 4:21 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> Another instance reported here:
> https://groups.google.com/d/msg/syzkaller-bugs/X6iDmVKBf2U/AHyJlnyaAgAJ
>
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.13.0-rc6-next-20170824+ #8 Not tainted
> ------------------------------------------------------
> kworker/u4:2/57 is trying to acquire lock:
> ((complete)&rcu.completion){+.+.}, at: [<ffffffff815afff5>]
> __synchronize_srcu+0x1b5/0x250 kernel/rcu/srcutree.c:898
>
> but task is already holding lock:
> (slab_mutex){+.+.}, at: [<ffffffff8192b730>] kmem_cache_destroy+0x30/0x250
> mm/slab_common.c:821
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #3 (slab_mutex){+.+.}:
> check_prevs_add kernel/locking/lockdep.c:2020 [inline]
> validate_chain kernel/locking/lockdep.c:2469 [inline]
> __lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
> lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
> __mutex_lock_common kernel/locking/mutex.c:756 [inline]
> __mutex_lock+0x16f/0x1870 kernel/locking/mutex.c:893
> mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
> kmem_cache_create+0x39/0x2a0 mm/slab_common.c:435
> ptlock_cache_init+0x24/0x2d mm/memory.c:4632
> pgtable_init include/linux/mm.h:1756 [inline]
> mm_init init/main.c:504 [inline]
> start_kernel+0x3d4/0x7ad init/main.c:569
> x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:381
> x86_64_start_kernel+0x13c/0x149 arch/x86/kernel/head64.c:362
> verify_cpu+0x0/0xfb
>
> -> #2 (memcg_cache_ids_sem){.+.+}:
> check_prevs_add kernel/locking/lockdep.c:2020 [inline]
> validate_chain kernel/locking/lockdep.c:2469 [inline]
> __lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
> lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
> down_read+0x96/0x150 kernel/locking/rwsem.c:23
> memcg_get_cache_ids+0x10/0x20 mm/memcontrol.c:274
> list_lru_destroy+0x96/0x490 mm/list_lru.c:573
> deactivate_locked_super+0x94/0xd0 fs/super.c:315
> deactivate_super+0x141/0x1b0 fs/super.c:339
> cleanup_mnt+0xb2/0x150 fs/namespace.c:1113
> mntput_no_expire+0x6e0/0xa90 fs/namespace.c:1179
> mntput fs/namespace.c:1189 [inline]
> kern_unmount+0x9c/0xd0 fs/namespace.c:2934
> pid_ns_release_proc+0x37/0x50 fs/proc/root.c:231
> proc_cleanup_work+0x19/0x20 kernel/pid_namespace.c:79
> process_one_work+0xbfd/0x1be0 kernel/workqueue.c:2098
> worker_thread+0x223/0x1860 kernel/workqueue.c:2233
> kthread+0x39c/0x470 kernel/kthread.c:231
> ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>
> -> #1 ((&ns->proc_work)){+.+.}:
> process_one_work+0xba5/0x1be0 kernel/workqueue.c:2095
> worker_thread+0x223/0x1860 kernel/workqueue.c:2233
> kthread+0x39c/0x470 kernel/kthread.c:231
> ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
> 0xffffffffffffffff
>
> -> #0 ((complete)&rcu.completion){+.+.}:
> check_prev_add+0x865/0x1520 kernel/locking/lockdep.c:1894
> check_prevs_add kernel/locking/lockdep.c:2020 [inline]
> validate_chain kernel/locking/lockdep.c:2469 [inline]
> __lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
> lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
> complete_acquire include/linux/completion.h:39 [inline]
> __wait_for_common kernel/sched/completion.c:108 [inline]
> wait_for_common kernel/sched/completion.c:122 [inline]
> wait_for_completion+0xc8/0x770 kernel/sched/completion.c:143
> __synchronize_srcu+0x1b5/0x250 kernel/rcu/srcutree.c:898
> synchronize_srcu_expedited kernel/rcu/srcutree.c:923 [inline]
> synchronize_srcu+0x1a3/0x560 kernel/rcu/srcutree.c:974
> quarantine_remove_cache+0xd7/0xf0 mm/kasan/quarantine.c:327
> kasan_cache_shutdown+0x9/0x10 mm/kasan/kasan.c:381
> shutdown_cache+0x15/0x1b0 mm/slab_common.c:531
> kmem_cache_destroy+0x236/0x250 mm/slab_common.c:829
> tipc_server_stop+0x13f/0x190 net/tipc/server.c:636
> tipc_topsrv_stop+0x1fe/0x350 net/tipc/subscr.c:390
> tipc_exit_net+0x15/0x40 net/tipc/core.c:96
> ops_exit_list.isra.6+0xae/0x150 net/core/net_namespace.c:142
> cleanup_net+0x5c7/0xb60 net/core/net_namespace.c:483
> process_one_work+0xbfd/0x1be0 kernel/workqueue.c:2098
> worker_thread+0x223/0x1860 kernel/workqueue.c:2233
> kthread+0x39c/0x470 kernel/kthread.c:231
> ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>
> other info that might help us debug this:
>
> Chain exists of:
> (complete)&rcu.completion --> memcg_cache_ids_sem --> slab_mutex
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(slab_mutex);
> lock(memcg_cache_ids_sem);
> lock(slab_mutex);
> lock((complete)&rcu.completion);
>
> *** DEADLOCK ***
>
> 5 locks held by kworker/u4:2/57:
> #0: ("%s""netns"){.+.+}, at: [<ffffffff81464534>] __write_once_size
> include/linux/compiler.h:305 [inline]
> #0: ("%s""netns"){.+.+}, at: [<ffffffff81464534>] atomic64_set
> arch/x86/include/asm/atomic64_64.h:33 [inline]
> #0: ("%s""netns"){.+.+}, at: [<ffffffff81464534>] atomic_long_set
> include/asm-generic/atomic-long.h:56 [inline]
> #0: ("%s""netns"){.+.+}, at: [<ffffffff81464534>] set_work_data
> kernel/workqueue.c:617 [inline]
> #0: ("%s""netns"){.+.+}, at: [<ffffffff81464534>]
> set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
> #0: ("%s""netns"){.+.+}, at: [<ffffffff81464534>]
> process_one_work+0xad4/0x1be0 kernel/workqueue.c:2090
> #1: (net_cleanup_work){+.+.}, at: [<ffffffff8146458c>]
> process_one_work+0xb2c/0x1be0 kernel/workqueue.c:2094
> #2: (net_mutex){+.+.}, at: [<ffffffff83e50bc7>] cleanup_net+0x247/0xb60
> net/core/net_namespace.c:449
> #3: (cpu_hotplug_lock.rw_sem){++++}, at: [<ffffffff8192b722>]
> get_online_cpus include/linux/cpu.h:126 [inline]
> #3: (cpu_hotplug_lock.rw_sem){++++}, at: [<ffffffff8192b722>]
> kmem_cache_destroy+0x22/0x250 mm/slab_common.c:818
> #4: (slab_mutex){+.+.}, at: [<ffffffff8192b730>]
> kmem_cache_destroy+0x30/0x250 mm/slab_common.c:821
>
> stack backtrace:
> CPU: 1 PID: 57 Comm: kworker/u4:2 Not tainted 4.13.0-rc6-next-20170824+ #8
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: netns cleanup_net
> Call Trace:
> __dump_stack lib/dump_stack.c:16 [inline]
> dump_stack+0x194/0x257 lib/dump_stack.c:52
> print_circular_bug+0x503/0x710 kernel/locking/lockdep.c:1259
> check_prev_add+0x865/0x1520 kernel/locking/lockdep.c:1894
> check_prevs_add kernel/locking/lockdep.c:2020 [inline]
> validate_chain kernel/locking/lockdep.c:2469 [inline]
> __lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
> lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
> complete_acquire include/linux/completion.h:39 [inline]
> __wait_for_common kernel/sched/completion.c:108 [inline]
> wait_for_common kernel/sched/completion.c:122 [inline]
> wait_for_completion+0xc8/0x770 kernel/sched/completion.c:143
> __synchronize_srcu+0x1b5/0x250 kernel/rcu/srcutree.c:898
> synchronize_srcu_expedited kernel/rcu/srcutree.c:923 [inline]
> synchronize_srcu+0x1a3/0x560 kernel/rcu/srcutree.c:974
> quarantine_remove_cache+0xd7/0xf0 mm/kasan/quarantine.c:327
> kasan_cache_shutdown+0x9/0x10 mm/kasan/kasan.c:381
> shutdown_cache+0x15/0x1b0 mm/slab_common.c:531
> kmem_cache_destroy+0x236/0x250 mm/slab_common.c:829
> tipc_server_stop+0x13f/0x190 net/tipc/server.c:636
> tipc_topsrv_stop+0x1fe/0x350 net/tipc/subscr.c:390
> tipc_exit_net+0x15/0x40 net/tipc/core.c:96
> ops_exit_list.isra.6+0xae/0x150 net/core/net_namespace.c:142
> cleanup_net+0x5c7/0xb60 net/core/net_namespace.c:483
> process_one_work+0xbfd/0x1be0 kernel/workqueue.c:2098
> worker_thread+0x223/0x1860 kernel/workqueue.c:2233
> kthread+0x39c/0x470 kernel/kthread.c:231
> ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>
> On Mon, Oct 30, 2017 at 10:34 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>> On Mon, Oct 30, 2017 at 10:32 PM, syzbot
>> <bot+e24d104216808d90da4c438a6f38a239217c605b@xxxxxxxxxxxxxxxxxxxxxxxxx>
>> wrote:
>>> Hello,
>>>
>>> syzkaller hit the following crash on
>>> 9506597de2cde02d48c11d5c250250b9143f59f7
>>> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
>>> compiler: gcc (GCC) 7.1.1 20170620
>>> .config is attached
>>> Raw console output is attached.
>>> C reproducer is attached
>>> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
>>> for information about syzkaller reproducers
>>>
>>>
>>> ======================================================
>>> WARNING: possible circular locking dependency detected
>>> 4.13.0-rc6-next-20170824+ #8 Not tainted
>>> ------------------------------------------------------
>>> kworker/0:2/1313 is trying to acquire lock:
>>> ((shepherd).work){+.+.}, at: [<ffffffff8146458c>]
>>> process_one_work+0xb2c/0x1be0 kernel/workqueue.c:2094
>>>
>>> but now in release context of a crosslock acquired at the following:
>>> ((complete)&rcu.completion){+.+.}, at: [<ffffffff815afff5>]
>>> __synchronize_srcu+0x1b5/0x250 kernel/rcu/srcutree.c:898
>>>
>>> which lock already depends on the new lock.
>>>
>>>
>>> the existing dependency chain (in reverse order) is:
>>>
>>> -> #2 ((complete)&rcu.completion){+.+.}:
>>> check_prevs_add kernel/locking/lockdep.c:2020 [inline]
>>> validate_chain kernel/locking/lockdep.c:2469 [inline]
>>> __lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
>>> lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
>>> complete_acquire include/linux/completion.h:39 [inline]
>>> __wait_for_common kernel/sched/completion.c:108 [inline]
>>> wait_for_common kernel/sched/completion.c:122 [inline]
>>> wait_for_completion+0xc8/0x770 kernel/sched/completion.c:143
>>> __synchronize_srcu+0x1b5/0x250 kernel/rcu/srcutree.c:898
>>> synchronize_srcu_expedited kernel/rcu/srcutree.c:923 [inline]
>>> synchronize_srcu+0x1a3/0x560 kernel/rcu/srcutree.c:974
>>
>> This looks like an issue with KASAN, which unexpectedly calls
>> synchronize_srcu from kmem_cache_shrink.
>> So +kasan-dev, Tejun, Lai to BCC.
>>
>>
>>> quarantine_remove_cache+0xd7/0xf0 mm/kasan/quarantine.c:327
>>> kasan_cache_shrink+0x9/0x10 mm/kasan/kasan.c:380
>>> kmem_cache_shrink+0x15/0x30 mm/slab_common.c:857
>>> acpi_os_purge_cache+0x15/0x20 drivers/acpi/osl.c:1560
>>> acpi_purge_cached_objects+0x38/0xc9 drivers/acpi/acpica/utxface.c:271
>>> acpi_initialize_objects+0xc5/0x112 drivers/acpi/acpica/utxfinit.c:302
>>> acpi_bus_init drivers/acpi/bus.c:1131 [inline]
>>> acpi_init+0x23c/0x8e6 drivers/acpi/bus.c:1220
>>> do_one_initcall+0x9e/0x330 init/main.c:826
>>> do_initcall_level init/main.c:892 [inline]
>>> do_initcalls init/main.c:900 [inline]
>>> do_basic_setup init/main.c:918 [inline]
>>> kernel_init_freeable+0x469/0x521 init/main.c:1066
>>> kernel_init+0x13/0x172 init/main.c:993
>>> ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>>>
>>> -> #1 (cpu_hotplug_lock.rw_sem){++++}:
>>> check_prevs_add kernel/locking/lockdep.c:2020 [inline]
>>> validate_chain kernel/locking/lockdep.c:2469 [inline]
>>> __lock_acquire+0x3286/0x4620 kernel/locking/lockdep.c:3498
>>> lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002
>>> percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:35
>>> [inline]
>>> percpu_down_read include/linux/percpu-rwsem.h:58 [inline]
>>> cpus_read_lock+0x42/0x90 kernel/cpu.c:218
>>> get_online_cpus include/linux/cpu.h:126 [inline]
>>> vmstat_shepherd+0x3d/0x1b0 mm/vmstat.c:1707
>>> process_one_work+0xbfd/0x1be0 kernel/workqueue.c:2098
>>> worker_thread+0x223/0x1860 kernel/workqueue.c:2233
>>> kthread+0x39c/0x470 kernel/kthread.c:231
>>> ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>>>
>>> -> #0 ((shepherd).work){+.+.}:
>>> process_one_work+0xba5/0x1be0 kernel/workqueue.c:2095
>>> worker_thread+0x223/0x1860 kernel/workqueue.c:2233
>>> kthread+0x39c/0x470 kernel/kthread.c:231
>>> ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>>> 0xffffffffffffffff
>>>
>>> other info that might help us debug this:
>>>
>>> Chain exists of:
>>> (shepherd).work --> cpu_hotplug_lock.rw_sem --> (complete)&rcu.completion
>>>
>>> Possible unsafe locking scenario by crosslock:
>>>
>>> CPU0 CPU1
>>> ---- ----
>>> lock(cpu_hotplug_lock.rw_sem);
>>> lock((complete)&rcu.completion);
>>> lock((shepherd).work);
>>> unlock((complete)&rcu.completion);
>>>
>>> *** DEADLOCK ***
>>>
>>> 3 locks held by kworker/0:2/1313:
>>> #0: ("events_power_efficient"){.+.+}, at: [<ffffffff81464534>]
>>> __write_once_size include/linux/compiler.h:305 [inline]
>>> #0: ("events_power_efficient"){.+.+}, at: [<ffffffff81464534>]
>>> atomic64_set arch/x86/include/asm/atomic64_64.h:33 [inline]
>>> #0: ("events_power_efficient"){.+.+}, at: [<ffffffff81464534>]
>>> atomic_long_set include/asm-generic/atomic-long.h:56 [inline]
>>> #0: ("events_power_efficient"){.+.+}, at: [<ffffffff81464534>]
>>> set_work_data kernel/workqueue.c:617 [inline]
>>> #0: ("events_power_efficient"){.+.+}, at: [<ffffffff81464534>]
>>> set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
>>> #0: ("events_power_efficient"){.+.+}, at: [<ffffffff81464534>]
>>> process_one_work+0xad4/0x1be0 kernel/workqueue.c:2090
>>> #1: ((&(&sdp->work)->work)){+.+.}, at: [<ffffffff8146458c>]
>>> process_one_work+0xb2c/0x1be0 kernel/workqueue.c:2094
>>> #2: (&x->wait#5){....}, at: [<ffffffff81524c68>] complete+0x18/0x80
>>> kernel/sched/completion.c:34
>>>
>>> stack backtrace:
>>> CPU: 0 PID: 1313 Comm: kworker/0:2 Not tainted 4.13.0-rc6-next-20170824+ #8
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>> Workqueue: events_power_efficient srcu_invoke_callbacks
>>> Call Trace:
>>> __dump_stack lib/dump_stack.c:16 [inline]
>>> dump_stack+0x194/0x257 lib/dump_stack.c:52
>>> print_circular_bug+0x503/0x710 kernel/locking/lockdep.c:1259
>>> check_prev_add+0x865/0x1520 kernel/locking/lockdep.c:1894
>>> commit_xhlock kernel/locking/lockdep.c:5002 [inline]
>>> commit_xhlocks kernel/locking/lockdep.c:5046 [inline]
>>> lock_commit_crosslock+0xe73/0x1d10 kernel/locking/lockdep.c:5085
>>> complete_release_commit include/linux/completion.h:49 [inline]
>>> complete+0x24/0x80 kernel/sched/completion.c:39
>>> wakeme_after_rcu+0xd/0x10 kernel/rcu/update.c:376
>>> srcu_invoke_callbacks+0x280/0x4d0 kernel/rcu/srcutree.c:1161
>>> process_one_work+0xbfd/0x1be0 kernel/workqueue.c:2098
>>> worker_thread+0x223/0x1860 kernel/workqueue.c:2233
>>> kthread+0x39c/0x470 kernel/kthread.c:231
>>> ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
>>>
>>>
>>> ---
>>> This bug is generated by a dumb bot. It may contain errors.
>>> See https://goo.gl/tpsmEJ for details.
>>> Direct all questions to syzkaller@xxxxxxxxxxxxxxxxx
>>>
>>> syzbot will keep track of this bug report.
>>> Once a fix for this bug is committed, please reply to this email with:
>>> #syz fix: exact-commit-title
>>> To mark this as a duplicate of another syzbot report, please reply with:
>>> #syz dup: exact-subject-of-another-report
>>> If it's a one-off invalid bug report, please reply with:
>>> #syz invalid
>>> Note: if the crash happens again, it will cause creation of a new bug
>>> report.
>>>
>>> --
>>> You received this message because you are subscribed to the Google Groups
>>> "syzkaller-bugs" group.
>>> To unsubscribe from this group and stop receiving emails from it, send an
>>> email to syzkaller-bugs+unsubscribe@xxxxxxxxxxxxxxxxx
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