Scheduler tracepoints stat_sleep, stat_iowait, stat_blocked and stat_runtime require the kernel parameter schedstats=enable or kernel.sched_schedstats=1 INFO: task syz-executor386:8116 blocked for more than 140 seconds. Not tainted 4.19.211-syzkaller #0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. syz-executor386 D27216 8116 8115 0x00000004 Call Trace: context_switch kernel/sched/core.c:2828 [inline] __schedule+0x887/0x2040 kernel/sched/core.c:3517 schedule+0x8d/0x1b0 kernel/sched/core.c:3561 schedule_timeout+0x92d/0xfe0 kernel/time/timer.c:1794 do_wait_for_common kernel/sched/completion.c:83 [inline] __wait_for_common kernel/sched/completion.c:104 [inline] wait_for_common+0x29c/0x470 kernel/sched/completion.c:115 __flush_work+0x4bb/0x8b0 kernel/workqueue.c:2926 n_tty_poll+0x54d/0x8f0 drivers/tty/n_tty.c:2410 tty_poll+0x139/0x1b0 drivers/tty/tty_io.c:2110 vfs_poll include/linux/poll.h:90 [inline] do_select+0x8e1/0x1610 fs/select.c:507 core_sys_select+0x3ac/0x7e0 fs/select.c:650 do_pselect fs/select.c:731 [inline] __do_sys_pselect6 fs/select.c:772 [inline] __se_sys_pselect6+0x419/0x480 fs/select.c:757 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x7f825ede13c9 Code: Bad RIP value. RSP: 002b:00007ffd2335cbb8 EFLAGS: 00000246 ORIG_RAX: 000000000000010e RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f825ede13c9 RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000000000040 RBP: 00007ffd2335cbf0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000020000140 R11: 0000000000000246 R12: 00007f825eda4990 R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000 Showing all locks held in the system: 6 locks held by kworker/u4:2/37: 1 lock held by khungtaskd/1571: #0: 000000007fc17b8b (rcu_read_lock){....}, at: debug_show_all_locks+0x53/0x265 kernel/locking/lockdep.c:4441 1 lock held by in:imklog/7811: #0: 0000000073ced209 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x26f/0x310 fs/file.c:767 1 lock held by syz-executor386/8116: #0: 00000000d2b5d8e0 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:272 ============================================= NMI backtrace for cpu 0 CPU: 0 PID: 1571 Comm: khungtaskd Not tainted 4.19.211-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+0x1fc/0x2ef lib/dump_stack.c:118 nmi_cpu_backtrace.cold+0x63/0xa2 lib/nmi_backtrace.c:101 nmi_trigger_cpumask_backtrace+0x1a6/0x1f0 lib/nmi_backtrace.c:62 trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline] check_hung_uninterruptible_tasks kernel/hung_task.c:203 [inline] watchdog+0x991/0xe60 kernel/hung_task.c:287 kthread+0x33f/0x460 kernel/kthread.c:259 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415 Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 CPU: 1 PID: 37 Comm: kworker/u4:2 Not tainted 4.19.211-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: events_unbound flush_to_ldisc RIP: 0010:preempt_count arch/x86/include/asm/preempt.h:23 [inline] RIP: 0010:check_kcov_mode kernel/kcov.c:67 [inline] RIP: 0010:write_comp_data+0xf/0x70 kernel/kcov.c:122 Code: 8b 11 48 83 c2 01 48 39 d0 76 07 48 89 34 d1 48 89 11 c3 0f 1f 84 00 00 00 00 00 49 89 f1 49 89 fa 65 48 8b 34 25 c0 df 01 00 <65> 8b 05 7a 59 9f 7e a9 00 01 1f 00 75 4f 8b 86 60 13 00 00 83 f8 RSP: 0018:ffff8880b5147938 EFLAGS: 00000046 RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffffffff813d5d0f RDX: 0000000000000001 RSI: ffff8880b51382c0 RDI: 0000000000000005 RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000005 R11: 0000000000000000 R12: ffff88813bfcd080 R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000008 FS: 0000000000000000(0000) GS:ffff8880ba100000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00005555568bb2c0 CR3: 00000000a8814000 CR4: 00000000003406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: unbound_pwq_by_node+0x1f/0x180 kernel/workqueue.c:564 __queue_work+0x19f/0x1100 kernel/workqueue.c:1391 queue_work_on+0x17e/0x1f0 kernel/workqueue.c:1489 pty_write+0x195/0x1f0 drivers/tty/pty.c:126 tty_put_char+0x122/0x150 drivers/tty/tty_io.c:2893 __process_echoes+0x583/0x9f0 drivers/tty/n_tty.c:727 flush_echoes drivers/tty/n_tty.c:827 [inline] __receive_buf drivers/tty/n_tty.c:1646 [inline] n_tty_receive_buf_common+0xc0c/0x2a90 drivers/tty/n_tty.c:1740 tty_ldisc_receive_buf+0xa9/0x190 drivers/tty/tty_buffer.c:456 tty_port_default_receive_buf+0x78/0xa0 drivers/tty/tty_port.c:38 receive_buf drivers/tty/tty_buffer.c:476 [inline] flush_to_ldisc+0x21f/0x390 drivers/tty/tty_buffer.c:528 process_one_work+0x864/0x1570 kernel/workqueue.c:2153 worker_thread+0x64c/0x1130 kernel/workqueue.c:2296 kthread+0x33f/0x460 kernel/kthread.c:259 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415 ---------------- Code disassembly (best guess): 0: 8b 11 mov (%rcx),%edx 2: 48 83 c2 01 add $0x1,%rdx 6: 48 39 d0 cmp %rdx,%rax 9: 76 07 jbe 0x12 b: 48 89 34 d1 mov %rsi,(%rcx,%rdx,8) f: 48 89 11 mov %rdx,(%rcx) 12: c3 retq 13: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1) 1a: 00 1b: 49 89 f1 mov %rsi,%r9 1e: 49 89 fa mov %rdi,%r10 21: 65 48 8b 34 25 c0 df mov %gs:0x1dfc0,%rsi 28: 01 00 * 2a: 65 8b 05 7a 59 9f 7e mov %gs:0x7e9f597a(%rip),%eax # 0x7e9f59ab <-- trapping instruction 31: a9 00 01 1f 00 test $0x1f0100,%eax 36: 75 4f jne 0x87 38: 8b 86 60 13 00 00 mov 0x1360(%rsi),%eax 3e: 83 .byte 0x83 3f: f8 clc