syzbot


INFO: task hung in flush_to_ldisc (3)

Status: closed as invalid on 2022/02/08 10:26
Reported-by: syzbot+5864be6ce31bdf05e8ee@syzkaller.appspotmail.com
First crash: 384d, last: 191d

Cause bisection: the issue happens on the oldest tested release (bisect log)
Crash: INFO: task hung in flush_to_ldisc (log)
Repro: C syz .config
similar bugs (8):
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.19 INFO: task hung in flush_to_ldisc (2) 1 760d 760d 0/1 auto-closed as invalid on 2020/11/11 17:44
upstream INFO: task hung in flush_to_ldisc (2) 1 490d 490d 0/23 auto-closed as invalid on 2021/06/09 11:04
linux-4.19 INFO: task hung in flush_to_ldisc 10 909d 971d 0/1 auto-closed as invalid on 2020/06/15 14:09
upstream INFO: task hung in flush_to_ldisc C inconclusive done 15 911d 981d 17/23 fixed on 2020/11/16 12:12
linux-4.14 INFO: task hung in flush_to_ldisc (3) 1 522d 522d 0/1 auto-closed as invalid on 2021/07/07 16:40
linux-4.14 INFO: task hung in flush_to_ldisc (2) 1 713d 713d 0/1 auto-closed as invalid on 2020/12/28 13:53
linux-4.19 INFO: task hung in flush_to_ldisc (3) 1 474d 474d 0/1 auto-closed as invalid on 2021/08/25 00:39
linux-4.14 INFO: task hung in flush_to_ldisc 8 901d 972d 0/1 auto-closed as invalid on 2020/06/23 11:01

Sample crash report:
INFO: task kworker/u4:3:121 blocked for more than 143 seconds.
      Not tainted 5.14.0-rc4-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u4:3    state:D stack:18584 pid:  121 ppid:     2 flags:0x00004000
Workqueue: events_unbound flush_to_ldisc
Call Trace:
 context_switch kernel/sched/core.c:4683 [inline]
 __schedule+0xc07/0x11f0 kernel/sched/core.c:5940
 schedule+0x14b/0x210 kernel/sched/core.c:6019
 schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6078
 __mutex_lock_common+0x116f/0x3770 kernel/locking/mutex.c:1036
 __mutex_lock kernel/locking/mutex.c:1104 [inline]
 mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1119
 flush_to_ldisc+0x37/0x510 drivers/tty/tty_buffer.c:515
 process_one_work+0x833/0x10c0 kernel/workqueue.c:2276
 worker_thread+0xac1/0x1320 kernel/workqueue.c:2422
 kthread+0x453/0x480 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
INFO: task syz-executor558:8565 blocked for more than 143 seconds.
      Not tainted 5.14.0-rc4-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor558 state:D stack:25496 pid: 8565 ppid:  8458 flags:0x00004004
Call Trace:
 context_switch kernel/sched/core.c:4683 [inline]
 __schedule+0xc07/0x11f0 kernel/sched/core.c:5940
 schedule+0x14b/0x210 kernel/sched/core.c:6019
 schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6078
 __mutex_lock_common+0x116f/0x3770 kernel/locking/mutex.c:1036
 __mutex_lock kernel/locking/mutex.c:1104 [inline]
 mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1119
 set_selection_kernel+0x27/0x17d0 drivers/tty/vt/selection.c:357
 set_selection_user+0xaa/0xe0 drivers/tty/vt/selection.c:185
 vt_ioctl+0x455/0x37b0 drivers/tty/vt/vt_ioctl.c:760
 tty_ioctl+0xf51/0x1720 drivers/tty/tty_io.c:2805
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x443859
RSP: 002b:00007ffe12f3c308 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000443859
RDX: 0000000020000000 RSI: 000000000000541c RDI: 0000000000000003
RBP: 0000000000000000 R08: 000000000000000e R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe12f3c348
R13: 00007ffe12f3c360 R14: 00007ffe12f3c3a0 R15: 0000000000000027

Showing all locks held in the system:
3 locks held by kworker/u4:3/121:
 #0: ffff888011069138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x7aa/0x10c0 kernel/workqueue.c:2249
 #1: ffffc9000130fd20 ((work_completion)(&buf->work)){+.+.}-{0:0}, at: process_one_work+0x7e8/0x10c0 kernel/workqueue.c:2251
 #2: ffff8880317940b8 (&buf->lock){+.+.}-{3:3}, at: flush_to_ldisc+0x37/0x510 drivers/tty/tty_buffer.c:515
1 lock held by khungtaskd/1645:
 #0: ffffffff8c7177c0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30 arch/x86/pci/mmconfig_64.c:151
1 lock held by in:imklog/8147:
 #0: ffff888016df6870 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x24e/0x2f0 fs/file.c:974
3 locks held by syz-executor558/8564:
1 lock held by syz-executor558/8565:
 #0: ffffffff8cdda7c8 (vc_sel.lock){+.+.}-{3:3}, at: set_selection_kernel+0x27/0x17d0 drivers/tty/vt/selection.c:357

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

NMI backtrace for cpu 0
CPU: 0 PID: 1645 Comm: khungtaskd Not tainted 5.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1d3/0x29f lib/dump_stack.c:105
 nmi_cpu_backtrace+0x16c/0x190 lib/nmi_backtrace.c:105
 nmi_trigger_cpumask_backtrace+0x191/0x2f0 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:210 [inline]
 watchdog+0xd06/0xd50 kernel/hung_task.c:295
 kthread+0x453/0x480 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 8564 Comm: syz-executor558 Not tainted 5.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:check_kcov_mode kernel/kcov.c:165 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:218 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp8+0x2b/0x90 kernel/kcov.c:291
Code: 8b 04 24 65 48 8b 14 25 80 ef 01 00 65 8b 05 14 c6 81 7e a9 00 01 ff 00 74 10 a9 00 01 00 00 74 6a 83 ba 34 15 00 00 00 74 61 <8b> 82 10 15 00 00 83 f8 03 75 56 48 8b 8a 18 15 00 00 44 8b 8a 14
RSP: 0018:ffffc9000160f6d8 EFLAGS: 00000246
RAX: 0000000080000000 RBX: 0000000000004002 RCX: ffffffff84752084
RDX: ffff8880296dd4c0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc9000160f7f0 R08: ffffffff847520ab R09: ffffed10052dba99
R10: ffffed10052dba99 R11: 0000000000000000 R12: ffff888146207438
R13: ffff8880296dd4c0 R14: dffffc0000000000 R15: dffffc0000000000
FS:  0000000001e513c0(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004bdee8 CR3: 0000000014be1000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 paste_selection+0x28b/0x500 drivers/tty/vt/selection.c:396
 vt_ioctl+0x455/0x37b0 drivers/tty/vt/vt_ioctl.c:760
 tty_ioctl+0xf51/0x1720 drivers/tty/tty_io.c:2805
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x443859
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 d1 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c4 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe12f3c308 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000443859
RDX: 0000000020000000 RSI: 000000000000541c RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000000e R11: 0000000000000246 R12: 00007ffe12f3c348
R13: 00007ffe12f3c360 R14: 00007ffe12f3c3a0 R15: 0000000000000026

Fix bisection attempts:
Manager Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Title
ci-upstream-kasan-gce-smack-root 2022/02/04 03:23 upstream dcb85f85fa6f 6c236867 .config log report syz C
ci-upstream-kasan-gce-smack-root 2022/01/04 20:48 upstream c9e6606c7fe9 6c236867 .config log report syz C
ci-upstream-kasan-gce-smack-root 2021/12/05 20:11 upstream 944207047ca4 6c236867 .config log report syz C
ci-upstream-kasan-gce-smack-root 2021/11/05 19:27 upstream fe91c4725aee 6c236867 .config log report syz C
ci-upstream-kasan-gce-smack-root 2021/10/06 18:32 upstream 60a9483534ed 6c236867 .config log report syz C
ci-upstream-kasan-gce-smack-root 2021/09/06 14:56 upstream 27151f177827 6c236867 .config log report syz C
Crashes (3):
Manager Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Title
ci-upstream-kasan-gce-smack-root 2021/08/03 08:41 upstream c500bee1c5b2 6c236867 .config log report syz C INFO: task hung in flush_to_ldisc
ci-upstream-kasan-gce-root 2021/07/25 18:46 upstream 6498f6151825 4d1b57d4 .config log report syz C INFO: task hung in flush_to_ldisc
ci-upstream-kasan-gce-smack-root 2021/07/28 09:54 upstream 7d549995d4e0 17d6ab15 .config log report info INFO: task hung in flush_to_ldisc