INFO: task hung in copy_net_ns (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: d08574b6 ANDROID: cuttlefish_defconfig: Enable VIRTIO_INPUT
git tree: android-4.4
console output: https://syzkaller.appspot.com/x/log.txt?x=14731b77400000
kernel config: https://syzkaller.appspot.com/x/.config?x=39bc4256ec37590
dashboard link: https://syzkaller.appspot.com/bug?extid=660af6c053b7d9166f73
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+660af6...@syzkaller.appspotmail.com

Free memory is 5372kB above reserved
lowmemorykiller: Killing 'syz-executor4' (10179) (tgid 10177), adj 1000,
to free 49732kB on behalf of 'rs:main Q:Reg' (1906) because
cache 7784kB is below limit 8192kB for oom_score_adj 1
Free memory is 5372kB above reserved
INFO: task syz-executor4:10179 blocked for more than 140 seconds.
Not tainted 4.4.169+ #2
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor4 D ffff8800b32c7968 28976 10179 2099 0x20120004
ffff8800b32c7968 ffff88007d065f00 a20fb13c5dc8bacf ffff88007d065f00
0000000000000000 ffff88007d066700 ffff8801db61f180 ffff8801db61f1a8
ffff8801db61e898 ffff8801d9e417c0 ffff88007d065f00 ffffed0016658001
Call Trace:
[<ffffffff827065e9>] schedule+0x99/0x1d0 kernel/sched/core.c:3355
[<ffffffff82706da3>] schedule_preempt_disabled+0x13/0x20
kernel/sched/core.c:3388
[<ffffffff82708f02>] __mutex_lock_common kernel/locking/mutex.c:582
[inline]
[<ffffffff82708f02>] mutex_lock_nested+0x3c2/0xb80
kernel/locking/mutex.c:621
[<ffffffff82217d6a>] copy_net_ns+0xca/0x250 net/core/net_namespace.c:387
[<ffffffff811368a0>] create_new_namespaces+0x2f0/0x670 kernel/nsproxy.c:95
[<ffffffff81136eaa>] copy_namespaces+0x28a/0x320 kernel/nsproxy.c:150
[<ffffffff810cd073>] copy_process+0x24d3/0x68c0 kernel/fork.c:1524
[<ffffffff810d188e>] _do_fork+0x14e/0xdc0 kernel/fork.c:1797
[<ffffffff810d25d7>] SYSC_clone kernel/fork.c:1908 [inline]
[<ffffffff810d25d7>] SyS_clone+0x37/0x50 kernel/fork.c:1902
[<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330
[inline]
[<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90
arch/x86/entry/common.c:397
[<ffffffff82716b50>] sysenter_flags_fixed+0xd/0x1a
lowmemorykiller: Killing 'syz-executor4' (10179) (tgid 10177), adj 1000,
to free 49732kB on behalf of 'syz-fuzzer' (2073) because
cache 7784kB is below limit 8192kB for oom_score_adj 1
Free memory is 5372kB above reserved
lowmemorykiller: Killing 'syz-executor4' (10179) (tgid 10177), adj 1000,
to free 49732kB on behalf of 'cron' (1962) because
cache 7784kB is below limit 8192kB for oom_score_adj 1
Free memory is 5372kB above reserved
1 lock held by syz-executor4/10179:
#0: (net_mutex){+.+.+.}, at: [<ffffffff82217d6a>] copy_net_ns+0xca/0x250
net/core/net_namespace.c:387
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 20 Comm: khungtaskd Not tainted 4.4.169+ #2
task: ffff8801da6f4740 task.stack: ffff8800001d0000
RIP: 0010:[<ffffffff8109b617>] [<ffffffff8109b617>] _flat_send_IPI_mask
arch/x86/kernel/apic/apic_flat_64.c:62 [inline]
RIP: 0010:[<ffffffff8109b617>] [<ffffffff8109b617>]
flat_send_IPI_mask+0xf7/0x1b0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8800001d7c88 EFLAGS: 00000046
RAX: 0000000000000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fc300
RBP: ffff8800001d7cb8 R08: 0000000000000018 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000003000000 R14: ffffffff82e5f2e0 R15: 0000000000000002
FS: 0000000000000000(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000ea90a8 CR3: 00000000bbbe8000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
0000000000000001 ffffffff82e5f2e0 ffffffff831a6340 fffffbfff0634b44
000000000001b6c0 0000000000000008 ffff8800001d7cd8 ffffffff81092bee
0000000000000008 ffffffff829241a0 ffff8800001d7d30 ffffffff81ab6a72
Call Trace:
[<ffffffff81092bee>] nmi_raise_cpu_backtrace+0x5e/0x80
arch/x86/kernel/apic/hw_nmi.c:33
[<ffffffff81ab6a72>] nmi_trigger_all_cpu_backtrace.cold+0xa1/0xae
lib/nmi_backtrace.c:85
[<ffffffff81092ca4>] arch_trigger_all_cpu_backtrace+0x14/0x20
arch/x86/kernel/apic/hw_nmi.c:38
[<ffffffff813b4576>] trigger_all_cpu_backtrace include/linux/nmi.h:44
[inline]
[<ffffffff813b4576>] check_hung_task kernel/hung_task.c:125 [inline]
[<ffffffff813b4576>] check_hung_uninterruptible_tasks
kernel/hung_task.c:182 [inline]
[<ffffffff813b4576>] watchdog.cold+0xd3/0xee kernel/hung_task.c:238
[<ffffffff811340d3>] kthread+0x273/0x310 kernel/kthread.c:211
[<ffffffff827157c5>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:537
Code: 00 c3 5f ff 80 e6 10 75 e1 41 c1 e5 18 44 89 2c 25 10 c3 5f ff 44 89
fa 09 da 80 cf 04 41 83 ff 02 0f 44 d3 89 14 25 00 c3 5f ff <41> f7 c4 00
02 00 00 75 1e 4c 89 e7 57 9d 0f 1f 44 00 00 e8 01
NMI backtrace for cpu 1
CPU: 1 PID: 1962 Comm: cron Not tainted 4.4.169+ #2
task: ffff8800b8852f80 task.stack: ffff8801d6bd0000
RIP: 0010:[<ffffffff8211b594>] [<ffffffff8211b594>]
lowmem_scan+0x404/0xbf0 drivers/staging/android/lowmemorykiller.c:125
RSP: 0018:ffff8801d6bd7510 EFLAGS: 00000246
RAX: 1ffff1001725c970 RBX: ffff8800b55b1c00 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8211b574 RDI: ffff8800b92e4b80
RBP: ffff8801d6bd75b0 R08: ffff8800b92e4f18 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: dffffc0000000000
R13: ffff8800b92e4740 R14: 0000000000002046 R15: 00000000000003e8
FS: 00007fc1c5bc47a0(0000) GS:ffff8801db700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000040320a CR3: 00000001d6a97000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
ffffffff8211b3cf ffffffff000007aa 0000000000001e68 0000000000000246
ffffffff82ea7320 ffff8800b8852f80 0000000000000666 ffff8801d6bd7688
fffffbfff05c1200 0000204b00000800 ffff8800b92e4f18 ffff8801d0ca97c0
Call Trace:
[<ffffffff813ee402>] do_shrink_slab mm/vmscan.c:357 [inline]
[<ffffffff813ee402>] shrink_slab.part.0+0x402/0xb30 mm/vmscan.c:455
[<ffffffff813f6f4c>] shrink_slab mm/vmscan.c:425 [inline]
[<ffffffff813f6f4c>] shrink_zone+0x4bc/0x610 mm/vmscan.c:2448
[<ffffffff813f770f>] shrink_zones mm/vmscan.c:2603 [inline]
[<ffffffff813f770f>] do_try_to_free_pages mm/vmscan.c:2653 [inline]
[<ffffffff813f770f>] try_to_free_pages+0x66f/0x1260 mm/vmscan.c:2861
[<ffffffff813d07bf>] __perform_reclaim mm/page_alloc.c:2915 [inline]
[<ffffffff813d07bf>] __alloc_pages_direct_reclaim mm/page_alloc.c:2936
[inline]
[<ffffffff813d07bf>] __alloc_pages_slowpath mm/page_alloc.c:3201 [inline]
[<ffffffff813d07bf>] __alloc_pages_nodemask+0x8af/0x14b0
mm/page_alloc.c:3313
[<ffffffff813bf5c9>] __alloc_pages include/linux/gfp.h:415 [inline]
[<ffffffff813bf5c9>] __alloc_pages_node include/linux/gfp.h:428 [inline]
[<ffffffff813bf5c9>] alloc_pages_node include/linux/gfp.h:442 [inline]
[<ffffffff813bf5c9>] __page_cache_alloc include/linux/pagemap.h:226
[inline]
[<ffffffff813bf5c9>] page_cache_read mm/filemap.c:1858 [inline]
[<ffffffff813bf5c9>] filemap_fault+0x829/0xc10 mm/filemap.c:2043
[<ffffffff81665842>] ext4_filemap_fault+0x72/0xa0 fs/ext4/inode.c:5558
[<ffffffff8142e34a>] __do_fault+0x1ca/0x350 mm/memory.c:2822
[<ffffffff8143b4ec>] do_read_fault mm/memory.c:3012 [inline]
[<ffffffff8143b4ec>] do_fault mm/memory.c:3177 [inline]
[<ffffffff8143b4ec>] handle_pte_fault mm/memory.c:3346 [inline]
[<ffffffff8143b4ec>] __handle_mm_fault mm/memory.c:3474 [inline]
[<ffffffff8143b4ec>] handle_mm_fault+0x1cfc/0x3140 mm/memory.c:3503
[<ffffffff810aaa4e>] __do_page_fault+0x28e/0x7f0 arch/x86/mm/fault.c:1243
[<ffffffff810ab008>] do_page_fault+0x28/0x30 arch/x86/mm/fault.c:1306
[<ffffffff82716635>] page_fault+0x25/0x30 arch/x86/entry/entry_64.S:1064
Code: 75 ac 48 89 5d b8 e8 8c de 1e ff 49 8d bd 40 04 00 00 48 89 f8 48 c1
e8 03 42 80 3c 20 00 0f 85 34 06 00 00 49 8b 9d 40 04 00 00 <4c> 8d ab c0
fb ff ff 48 81 fb 00 56 e1 82 0f 84 39 01 00 00 e8
lowmemorykiller: Killing 'syz-executor4' (10179) (tgid 10177), adj 1000,
to free 49732kB on behalf of 'syz-fuzzer' (2073) because
cache 7784kB is below limit 8192kB for oom_score_adj 1
Free memory is 5372kB above reserved
lowmemorykiller: Killing 'syz-executor4' (10179) (tgid 10177), adj 1000,
to free 49732kB on behalf of 'init' (1) because
cache 7784kB is below limit 8192kB for oom_score_adj 1
Free memory is 5372kB above reserved
lowmemorykiller: Killing 'syz-executor4' (10179) (tgid 10177), adj 1000,
to free 49732kB on behalf of 'syz-fuzzer' (2073) because
cache 7784kB is below limit 8192kB for oom_score_adj 1
Free memory is 5372kB above reserved
lowmemorykiller: Killing 'syz-executor4' (10179) (tgid 10177), adj 1000,
to free 49732kB on behalf of 'init' (1) because
cache 7784kB is below limit 8192kB for oom_score_adj 1
Free memory is 5372kB above reserved


---
This bug 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 bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.