syzbot

TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending cookies.  Check SNMP counters.
INFO: task syz-executor1:1632 blocked for more than 140 seconds.
      Not tainted 4.9.112-g9e79039 #59
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor1   D27992  1632   3896 0x00000004
 ffff8801a2113000 ffff88018cfc5f80 ffff8801bea08540 ffff88018e48c800
 ffff8801db321c18 ffff8801cd51f320 ffffffff839e907d 1ffff10039aa3e58
 ffffffff85542200 0000000041b58ab3 00ffffff843c36c0 ffff8801db3224e8
Call Trace:
 [<ffffffff839ea67f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839f6a91>] schedule_timeout+0x861/0xf70 kernel/time/timer.c:1768
 [<ffffffff839e885a>] io_schedule_timeout+0x1ba/0x390 kernel/sched/core.c:5180
 [<ffffffff816431db>] io_schedule include/linux/sched.h:460 [inline]
 [<ffffffff816431db>] dio_await_one fs/direct-io.c:461 [inline]
 [<ffffffff816431db>] dio_await_completion fs/direct-io.c:515 [inline]
 [<ffffffff816431db>] do_blockdev_direct_IO+0x2d5b/0x5a80 fs/direct-io.c:1331
 [<ffffffff81645fa5>] __blockdev_direct_IO+0xa5/0xd0 fs/direct-io.c:1360
 [<ffffffff8162fb50>] blkdev_direct_IO+0xa0/0xd0 fs/block_dev.c:183
 [<ffffffff8143e870>] generic_file_read_iter+0x660/0x1a90 mm/filemap.c:1951
 [<ffffffff81632755>] blkdev_read_iter+0x105/0x170 fs/block_dev.c:1738
 [<ffffffff81615159>] generic_file_splice_read+0x2c9/0x4f0 fs/splice.c:309
 [<ffffffff816138ac>] do_splice_to+0x10c/0x170 fs/splice.c:899
 [<ffffffff81613b4f>] splice_direct_to_actor+0x23f/0x7e0 fs/splice.c:971
 [<ffffffff81614293>] do_splice_direct+0x1a3/0x270 fs/splice.c:1080
 [<ffffffff81575680>] do_sendfile+0x4f0/0xc60 fs/read_write.c:1393
 [<ffffffff81577701>] SYSC_sendfile64 fs/read_write.c:1448 [inline]
 [<ffffffff81577701>] SyS_sendfile64+0xd1/0x160 fs/read_write.c:1440
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9f53>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136675c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136675c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425de7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3781:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f8122>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211edc2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142

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

NMI backtrace for cpu 0
CPU: 0 PID: 519 Comm: khungtaskd Not tainted 4.9.112-g9e79039 #59
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d859fd08 ffffffff81eb3249 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9bd0 ffff8801d859fd40
 ffffffff81ebe547 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3249>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3249>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebe547>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebe4da>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9cd4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366cf4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366cf4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366cf4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366cf4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d0bd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fa11c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff839f8b86