bisecting fixing commit since 13d2ce42de8cb98ff952f8de6307f896203854c2 building syzkaller on f213e07ead587b07a84e60c356520bce7277166c testing commit 13d2ce42de8cb98ff952f8de6307f896203854c2 with gcc (GCC) 8.1.0 kernel signature: e129f283082e87616f62a727b32736d647fcbd8cb238e96cb90e9e178a3b7529 run #0: crashed: INFO: task hung in n_tty_read run #1: crashed: INFO: task hung in n_tty_read run #2: crashed: INFO: task hung in n_tty_read run #3: crashed: INFO: task hung in n_tty_read run #4: crashed: INFO: task hung in n_tty_read run #5: crashed: INFO: task hung in n_tty_read run #6: crashed: INFO: task hung in n_tty_read run #7: crashed: INFO: task hung in n_tty_read run #8: crashed: INFO: task hung in console_callback run #9: crashed: INFO: task hung in console_callback testing current HEAD 675cc038067f0e530471c56a7442935f84669d95 testing commit 675cc038067f0e530471c56a7442935f84669d95 with gcc (GCC) 8.1.0 kernel signature: 63379d251985a21f5f81b64b8ba3b6b017553573d9c665116fb2dfd3b5f880b1 all runs: crashed: INFO: task hung in n_tty_read revisions tested: 2, total time: 30m36.413276879s (build: 17m43.230791535s, test: 12m11.369074835s) the crash still happens on HEAD commit msg: Linux 4.19.167 crash: INFO: task hung in n_tty_read Bluetooth: hci0: command 0x0406 tx timeout Bluetooth: hci3: command 0x0406 tx timeout Bluetooth: hci2: command 0x0406 tx timeout Bluetooth: hci1: command 0x0406 tx timeout Bluetooth: hci4: command 0x0406 tx timeout INFO: task agetty:8017 blocked for more than 140 seconds. Not tainted 4.19.167-syzkaller #0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. agetty D27576 8017 1 0x00000000 Call Trace: context_switch kernel/sched/core.c:2828 [inline] __schedule+0x80c/0x1f70 kernel/sched/core.c:3517 schedule+0x7f/0x1b0 kernel/sched/core.c:3561 schedule_timeout+0x6f6/0xd20 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+0x3fb/0x5d0 kernel/sched/completion.c:115 wait_for_completion+0x18/0x20 kernel/sched/completion.c:136 __flush_work+0x3d5/0x7f0 kernel/workqueue.c:2928 flush_work+0xb/0x10 kernel/workqueue.c:2949 tty_buffer_flush_work+0xd/0xf drivers/tty/tty_buffer.c:613 n_tty_read+0x764/0x1910 drivers/tty/n_tty.c:2197 tty_read+0x148/0x250 drivers/tty/tty_io.c:867 __vfs_read+0xe3/0x880 fs/read_write.c:416 vfs_read+0xf9/0x2f0 fs/read_write.c:452 ksys_read+0x103/0x260 fs/read_write.c:579 __do_sys_read fs/read_write.c:589 [inline] __se_sys_read fs/read_write.c:587 [inline] __x64_sys_read+0x6e/0xb0 fs/read_write.c:587 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x7fcf8b97d910 Code: Bad RIP value. RSP: 002b:00007ffd86206f18 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 RAX: ffffffffffffffda RBX: 000000000000007e RCX: 00007fcf8b97d910 RDX: 0000000000000001 RSI: 00007ffd86206f7f RDI: 0000000000000000 RBP: 000000000000007f R08: ffffffffffffff98 R09: 00007ffd86205dd0 R10: 000000000000051b R11: 0000000000000246 R12: 0000000000000000 R13: 0000564a098d1918 R14: 00007ffd86206f80 R15: 0000000000000012 Showing all locks held in the system: 7 locks held by kworker/u4:0/7: 1 lock held by khungtaskd/1565: #0: 000000001c9980c1 (rcu_read_lock){....}, at: debug_show_all_locks+0x5b/0x27a kernel/locking/lockdep.c:4442 1 lock held by in:imklog/7791: #0: 000000001e0416b2 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xa7/0xd0 fs/file.c:767 2 locks held by agetty/8017: #0: 0000000066b4c1d3 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x2d/0x40 drivers/tty/tty_ldsem.c:362 #1: 0000000053dba89d (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x1ee/0x1910 drivers/tty/n_tty.c:2154 2 locks held by kworker/1:3/8332: #0: 00000000ff1556b7 ((wq_completion)"events"){+.+.}, at: process_one_work+0x6e8/0x15a0 kernel/workqueue.c:2126 #1: 00000000e53af272 (console_work){+.+.}, at: process_one_work+0x71b/0x15a0 kernel/workqueue.c:2130 ============================================= NMI backtrace for cpu 0 CPU: 0 PID: 1565 Comm: khungtaskd Not tainted 4.19.167-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+0x17c/0x22a lib/dump_stack.c:118 nmi_cpu_backtrace.cold.0+0x3c/0x78 lib/nmi_backtrace.c:101 nmi_trigger_cpumask_backtrace+0xf6/0x11a lib/nmi_backtrace.c:62 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38 trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline] check_hung_uninterruptible_tasks kernel/hung_task.c:203 [inline] watchdog+0x5c3/0xb40 kernel/hung_task.c:287 kthread+0x347/0x410 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: 7 Comm: kworker/u4:0 Not tainted 4.19.167-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: events_unbound flush_to_ldisc RIP: 0010:vga16fb_fillrect+0x881/0x19b0 drivers/video/fbdev/vga16fb.c:924 Code: 8d 70 ff 85 c0 0f 84 30 fd ff ff 4c 63 7d c8 41 8d 7c 24 ff 31 d2 48 83 c7 01 49 8d 04 3e 45 85 e4 0f 84 0b 07 00 00 41 88 16 <49> 83 c6 01 49 39 c6 75 f4 4e 8d 34 38 83 ee 01 83 fe ff 75 db e9 RSP: 0018:ffff8880b5997420 EFLAGS: 00000287 RAX: ffff8880000a0050 RBX: 0000000000000000 RCX: 00000000ffffffb0 RDX: 0000000000000000 RSI: 00000000a7957afb RDI: 0000000000000050 RBP: ffff8880b5997498 R08: ffff8880b59974e4 R09: 0000000000000000 R10: 1ffff110277c4eb9 R11: 0000000000000000 R12: 0000000000000050 R13: 1ffffffff1322472 R14: ffff8880000a001a R15: ffffffffffffffb0 FS: 0000000000000000(0000) GS:ffff8880ba300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055ef99c5df48 CR3: 00000000a3322000 CR4: 00000000001406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: bit_clear+0x319/0x630 drivers/video/fbdev/core/bitblit.c:74 fbcon_clear+0x475/0x700 drivers/video/fbdev/core/fbcon.c:1258 fbcon_scroll+0x4f7/0x351c drivers/video/fbdev/core/fbcon.c:1756 con_scroll+0x467/0x700 drivers/tty/vt/vt.c:637 lf+0x23b/0x2a0 drivers/tty/vt/vt.c:1491 do_con_write.part.13+0x10f7/0x1aa0 drivers/tty/vt/vt.c:2768 do_con_write drivers/tty/vt/vt.c:3156 [inline] con_put_char+0xaf/0xc0 drivers/tty/vt/vt.c:3155 tty_put_char+0xac/0x130 drivers/tty/tty_io.c:2892 do_output_char+0x1c9/0x700 drivers/tty/n_tty.c:486 __process_echoes+0x287/0x790 drivers/tty/n_tty.c:737 commit_echoes+0x10e/0x160 drivers/tty/n_tty.c:792 n_tty_receive_char_fast drivers/tty/n_tty.c:1447 [inline] n_tty_receive_buf_fast drivers/tty/n_tty.c:1607 [inline] __receive_buf drivers/tty/n_tty.c:1642 [inline] n_tty_receive_buf_common+0x1363/0x2da0 drivers/tty/n_tty.c:1740 n_tty_receive_buf2+0xf/0x20 drivers/tty/n_tty.c:1775 tty_ldisc_receive_buf+0x86/0x1b0 drivers/tty/tty_buffer.c:456 tty_port_default_receive_buf+0x5f/0x90 drivers/tty/tty_port.c:38 receive_buf drivers/tty/tty_buffer.c:476 [inline] flush_to_ldisc+0x1aa/0x3a0 drivers/tty/tty_buffer.c:528 process_one_work+0x7b9/0x15a0 kernel/workqueue.c:2155 worker_thread+0x85/0xb60 kernel/workqueue.c:2298 kthread+0x347/0x410 kernel/kthread.c:259 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415