INFO: task hung in copy_net_ns

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: e7f51a5b ANDROID: sdcardfs: Set num in extension_details d..
git tree: android-4.9
console output: https://syzkaller.appspot.com/x/log.txt?x=17e0c8e3800000
kernel config: https://syzkaller.appspot.com/x/.config?x=6181e2689c6bb69b
dashboard link: https://syzkaller.appspot.com/bug?extid=44f066934a5bf9fc3ca5
compiler: gcc (GCC) 7.1.1 20170620
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1670d9a3800000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13d289a3800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+44f066...@syzkaller.appspotmail.com

IPVS: Unknown mcast interface: �/./�
IPVS: Unknown mcast interface: �/./�
IPVS: Unknown mcast interface: �/./�
IPVS: Unknown mcast interface: �/./�
IPVS: Unknown mcast interface: �/./�
INFO: task syzkaller976708:3763 blocked for more than 120 seconds.
Not tainted 4.9.84-ge7f51a5 #45
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syzkaller976708 D29216 3763 3761 0x00000000
ffff8801d7318000 0000000000000000 ffff8801d6de8fc0 ffff8801d951e000
ffff8801db221b98 ffff8801c2f87bc8 ffffffff838a438b 0000000000000000
0000000000000007 00ff8801d7318000 ffff8801db222468 ffff8801db222490
Call Trace:
[<ffffffff838a592f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
[<ffffffff838a62b3>] schedule_preempt_disabled+0x13/0x20
kernel/sched/core.c:3583
[<ffffffff838ab8c2>] __mutex_lock_common kernel/locking/mutex.c:582
[inline]
[<ffffffff838ab8c2>] mutex_lock_nested+0x312/0x870
kernel/locking/mutex.c:621
[<ffffffff82f1ebe5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387
[<ffffffff8119dd2f>] create_new_namespaces+0x37f/0x730 kernel/nsproxy.c:106
[<ffffffff8119e6be>] unshare_nsproxy_namespaces+0xae/0x1e0
kernel/nsproxy.c:205
[<ffffffff8113012d>] SYSC_unshare kernel/fork.c:2244 [inline]
[<ffffffff8113012d>] SyS_unshare+0x3dd/0x6f0 kernel/fork.c:2194
[<ffffffff81006504>] do_syscall_64+0x1a4/0x490 arch/x86/entry/common.c:282
[<ffffffff838b53fd>] entry_SYSCALL_64_after_swapgs+0x47/0xc5

Showing all locks held in the system:
2 locks held by khungtaskd/514:
#0: (rcu_read_lock){......}, at: [<ffffffff813730a5>]
check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
#0: (rcu_read_lock){......}, at: [<ffffffff813730a5>]
watchdog+0x125/0xa70 kernel/hung_task.c:239
#1: (tasklist_lock){.+.+..}, at: [<ffffffff81238190>]
debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/3485:
#0: (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d3bef>]
__fdget_pos+0x9f/0xc0 fs/file.c:781
2 locks held by getty/3613:
#0: (&tty->ldisc_sem){++++++}, at: [<ffffffff838b3602>]
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
#1: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8200ab14>]
n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
1 lock held by syzkaller976708/3763:
#0: (net_mutex){+.+.+.}, at: [<ffffffff82f1ebe5>] copy_net_ns+0x155/0x280
net/core/net_namespace.c:387
1 lock held by syzkaller976708/3764:
#0: (net_mutex){+.+.+.}, at: [<ffffffff82f1ebe5>] copy_net_ns+0x155/0x280
net/core/net_namespace.c:387
1 lock held by syzkaller976708/3766:
#0: (net_mutex){+.+.+.}, at: [<ffffffff82f1ebe5>] copy_net_ns+0x155/0x280
net/core/net_namespace.c:387
1 lock held by syzkaller976708/3767:
#0: (net_mutex){+.+.+.}, at: [<ffffffff82f1ebe5>] copy_net_ns+0x155/0x280
net/core/net_namespace.c:387
1 lock held by syzkaller976708/3768:
#0: (net_mutex){+.+.+.}, at: [<ffffffff82f1ebe5>] copy_net_ns+0x155/0x280
net/core/net_namespace.c:387
1 lock held by syzkaller976708/3769:
#0: (net_mutex){+.+.+.}, at: [<ffffffff82f1ebe5>] copy_net_ns+0x155/0x280
net/core/net_namespace.c:387

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

NMI backtrace for cpu 0
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.84-ge7f51a5 #45
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
ffff8801d859fd00 ffffffff81d956b9 0000000000000000 0000000000000000
0000000000000000 0000000000000001 ffffffff810bb190 ffff8801d859fd38
ffffffff81da07dd 0000000000000000 0000000000000000 ffff8801d7318418
Call Trace:
[<ffffffff81d956b9>] __dump_stack lib/dump_stack.c:15 [inline]
[<ffffffff81d956b9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
[<ffffffff81da07dd>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
[<ffffffff81da0917>] nmi_trigger_cpumask_backtrace+0x117/0x190
lib/nmi_backtrace.c:60
[<ffffffff810bb284>] arch_trigger_cpumask_backtrace+0x14/0x20
arch/x86/kernel/apic/hw_nmi.c:37
[<ffffffff81373670>] trigger_all_cpu_backtrace include/linux/nmi.h:58
[inline]
[<ffffffff81373670>] check_hung_task kernel/hung_task.c:125 [inline]
[<ffffffff81373670>] check_hung_uninterruptible_tasks
kernel/hung_task.c:182 [inline]
[<ffffffff81373670>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
[<ffffffff8119a7bd>] kthread+0x26d/0x300 kernel/kthread.c:211
[<ffffffff838b558c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:361
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 3765 Comm: syzkaller976708 Not tainted 4.9.84-ge7f51a5 #45
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
task: ffff8801d7b81800 task.stack: ffff8801c11f0000
RIP: 0010:[<ffffffff8203aeab>] c [<ffffffff8203aeab>] inb
arch/x86/include/asm/io.h:316 [inline]
RIP: 0010:[<ffffffff8203aeab>] c [<ffffffff8203aeab>]
io_serial_in+0x6b/0x90 drivers/tty/serial/8250/8250_port.c:414
RSP: 0018:ffff8801c11f7768 EFLAGS: 00000002
RAX: dffffc0000000000 RBX: 00000000000003fd RCX: 0000000000000000
RDX: 00000000000003fd RSI: 0000000000000005 RDI: ffffffff8627c478
RBP: ffff8801c11f7778 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff8627c440
R13: 0000000000000020 R14: fffffbfff0c4f8cf R15: fffffbfff0c4f891
FS: 0000000000a76880(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000471660 CR3: 00000001c12e0000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
ffffffff8627c440 c 0000000000002709 c ffff8801c11f77c8 c ffffffff8203cade c
ffffffff83a67a0d c ffffffff8627c488 c ffffffff8627c67a c ffffffff8627c440 c
000000000000006e c ffffffff8203cc20 c dffffc0000000000 c 000000000000006e c
Call Trace:
[<ffffffff8203cade>] serial_in drivers/tty/serial/8250/8250.h:111 [inline]
[<ffffffff8203cade>] wait_for_xmitr+0x8e/0x1d0
drivers/tty/serial/8250/8250_port.c:1997
[<ffffffff8203cc3f>] serial8250_console_putchar+0x1f/0x60
drivers/tty/serial/8250/8250_port.c:3103
[<ffffffff82024f0c>] uart_console_write+0xac/0xe0
drivers/tty/serial/serial_core.c:1857
[<ffffffff82048690>] serial8250_console_write+0x2e0/0x850
drivers/tty/serial/8250/8250_port.c:3169
[<ffffffff82035a7f>] univ8250_console_write+0x5f/0x70
drivers/tty/serial/8250/8250_core.c:594
[<ffffffff81265db5>] call_console_drivers.isra.20.constprop.29+0x1a5/0x350
kernel/printk/printk.c:1589
[<ffffffff81268a75>] console_unlock+0x425/0xb20 kernel/printk/printk.c:2445
[<ffffffff81269652>] vprintk_emit+0x4e2/0x750 kernel/printk/printk.c:1903
[<ffffffff812698e8>] vprintk+0x28/0x30 kernel/printk/printk.c:1913
[<ffffffff8126990d>] vprintk_default+0x1d/0x30 kernel/printk/printk.c:1914
[<ffffffff8143028c>] vprintk_func kernel/printk/internal.h:36 [inline]
[<ffffffff8143028c>] printk+0xb7/0xe2 kernel/printk/printk.c:1975
[<ffffffff8318f20f>] __ip_vs_init+0x3df/0x430
net/netfilter/ipvs/ip_vs_core.c:2243
[<ffffffff82f1d2f9>] ops_init+0xa9/0x3a0 net/core/net_namespace.c:111
[<ffffffff82f1d7a2>] setup_net+0x1b2/0x3e0 net/core/net_namespace.c:291
[<ffffffff82f1ec19>] copy_net_ns+0x189/0x280 net/core/net_namespace.c:389
[<ffffffff8119dd2f>] create_new_namespaces+0x37f/0x730 kernel/nsproxy.c:106
[<ffffffff8119e6be>] unshare_nsproxy_namespaces+0xae/0x1e0
kernel/nsproxy.c:205
[<ffffffff8113012d>] SYSC_unshare kernel/fork.c:2244 [inline]
[<ffffffff8113012d>] SyS_unshare+0x3dd/0x6f0 kernel/fork.c:2194
[<ffffffff81006504>] do_syscall_64+0x1a4/0x490 arch/x86/entry/common.c:282
[<ffffffff838b53fd>] entry_SYSCALL_64_after_swapgs+0x47/0xc5
Code: c24 cc9 c00 c00 c00 c49 c8d c7c c24 c38 c48 cb8 c00 c00
c00 c00 c00 cfc cff cdf c48 c89 cfa c48 cc1 cea c03 cd3 ce3
c80 c3c c02 c00 c75 c17 c41 c03 c5c c24 c38 c89 cda cec
c<5b> c0f cb6 cc0 c41 c5c c5d cc3 ce8 cf8 c38 c50 cff ceb
cc2 ce8 c51 c39 c50 cff ceb c


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