syzbot


INFO: task hung in con_flush_chars

Status: auto-closed as invalid on 2020/07/13 22:15
Subsystems: serial
[Documentation on labels]
First crash: 1955d, last: 1955d
Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in con_flush_chars (2) serial 1 2 1759d 1832d 0/29 auto-closed as invalid on 2021/01/25 20:43
upstream INFO: task hung in con_flush_chars (3) serial 1 1 1433d 1433d 0/29 auto-closed as invalid on 2021/12/18 10:46
upstream INFO: task hung in con_flush_chars (4) serial 1 4 153d 324d 0/29 auto-obsoleted due to no activity on 2025/06/20 07:50
linux-4.14 INFO: task hung in con_flush_chars 1 2 1991d 2008d 0/1 auto-closed as invalid on 2020/07/08 07:44

Sample crash report:
INFO: task syz-executor.0:17003 blocked for more than 143 seconds.
      Not tainted 5.7.0-rc1-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.0  D28128 17003   7011 0x00004004
Call Trace:
 context_switch kernel/sched/core.c:3372 [inline]
 __schedule+0x805/0xc90 kernel/sched/core.c:4088
 schedule+0x188/0x220 kernel/sched/core.c:4163
 schedule_timeout+0x43/0x250 kernel/time/timer.c:1874
 mark_held_locks kernel/locking/lockdep.c:3628 [inline]
 __trace_hardirqs_on_caller kernel/locking/lockdep.c:3657 [inline]
 lockdep_hardirqs_on+0x4a4/0x8a0 kernel/locking/lockdep.c:3702
 __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:168 [inline]
 _raw_spin_unlock_irq+0x1f/0x80 kernel/locking/spinlock.c:199
 __down_common+0x28a/0x520 kernel/locking/semaphore.c:220
 down+0x65/0xa0 kernel/locking/semaphore.c:61
 console_lock+0x24/0x70 kernel/printk/printk.c:2314
 con_flush_chars+0x57/0x640 drivers/tty/vt/vt.c:3230
 mark_held_locks kernel/locking/lockdep.c:3628 [inline]
 __trace_hardirqs_on_caller kernel/locking/lockdep.c:3657 [inline]
 lockdep_hardirqs_on+0x4a4/0x8a0 kernel/locking/lockdep.c:3702
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
 _raw_spin_unlock_irqrestore+0x6f/0xd0 kernel/locking/spinlock.c:191
 con_write+0x2a/0x40 drivers/tty/vt/vt.c:3154
 process_output_block drivers/tty/n_tty.c:595 [inline]
 n_tty_write+0xcbf/0x1170 drivers/tty/n_tty.c:2333
 wait_woken+0x240/0x240 kernel/sched/wait.c:442
 do_tty_write drivers/tty/tty_io.c:962 [inline]
 tty_write+0x593/0x940 drivers/tty/tty_io.c:1046
 n_tty_read+0x1bc0/0x1bc0 drivers/tty/n_tty.c:2186
 do_loop_readv_writev fs/read_write.c:718 [inline]
 do_iter_write+0x402/0x540 fs/read_write.c:1001
 vfs_writev fs/read_write.c:1072 [inline]
 do_writev+0x23f/0x4a0 fs/read_write.c:1115
 check_preemption_disabled+0xb0/0x240 lib/smp_processor_id.c:19
 debug_smp_processor_id+0x5/0x20 lib/smp_processor_id.c:56
 arch_static_branch arch/x86/include/asm/jump_label.h:25 [inline]
 static_key_false include/linux/jump_label.h:200 [inline]
 trace_irq_disable_rcuidle+0x1f/0x1d0 include/trace/events/preemptirq.h:36
 entry_SYSCALL_64_after_hwframe+0x3e/0xb3
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3
INFO: task syz-executor.2:17052 blocked for more than 143 seconds.
      Not tainted 5.7.0-rc1-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.2  D28560 17052   7201 0x00004004
Call Trace:
 context_switch kernel/sched/core.c:3372 [inline]
 __schedule+0x805/0xc90 kernel/sched/core.c:4088
 schedule+0x188/0x220 kernel/sched/core.c:4163
 schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:4222
 __mutex_lock_common+0x129f/0x2fc0 kernel/locking/mutex.c:1033
 lock_fb_info include/linux/fb.h:637 [inline]
 fb_open+0x14b/0x3b0 drivers/video/fbdev/core/fbmem.c:1418
 __mutex_lock kernel/locking/mutex.c:1103 [inline]
 mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1118
 lock_fb_info include/linux/fb.h:637 [inline]
 fb_open+0x14b/0x3b0 drivers/video/fbdev/core/fbmem.c:1418
 chrdev_open+0x498/0x580 fs/char_dev.c:414
 cd_forget+0x150/0x150 include/linux/spinlock.h:393
 do_dentry_open+0x82e/0x10b0 fs/open.c:797
 do_open fs/namei.c:3229 [inline]
 path_openat+0x2790/0x38b0 fs/namei.c:3346
 do_filp_open+0x191/0x3a0 fs/namei.c:3373
 __raw_spin_unlock include/linux/spinlock_api_smp.h:152 [inline]
 _raw_spin_unlock+0x24/0x40 kernel/locking/spinlock.c:183
 spin_unlock include/linux/spinlock.h:393 [inline]
 __alloc_fd+0x566/0x600 fs/file.c:534
 do_sys_openat2+0x463/0x770 fs/open.c:1148
 do_sys_open fs/open.c:1164 [inline]
 __do_sys_openat fs/open.c:1178 [inline]
 __se_sys_openat fs/open.c:1173 [inline]
 __x64_sys_openat+0x1c8/0x1f0 fs/open.c:1173
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3

Showing all locks held in the system:
1 lock held by khungtaskd/1136:
 #0: ffffffff892e8590 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30 net/mptcp/pm_netlink.c:858
1 lock held by in:imklog/6701:
 #0: ffff8880a14085f0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x25d/0x2f0 fs/file.c:826
4 locks held by syz-executor.0/17003:
 #0: ffff88808f3bd098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:267
 #1: ffff88808f3bd130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: tty_write_lock drivers/tty/tty_io.c:888 [inline]
 #1: ffff88808f3bd130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: do_tty_write drivers/tty/tty_io.c:911 [inline]
 #1: ffff88808f3bd130 (&tty->atomic_write_lock){+.+.}-{3:3}, at: tty_write+0x22c/0x940 drivers/tty/tty_io.c:1046
 #2: ffff88808f3bd2e8 (&tty->termios_rwsem){++++}-{3:3}, at: n_tty_write+0x1e0/0x1170 drivers/tty/n_tty.c:2316
 #3: ffffc90000fd0378 (&ldata->output_lock){+.+.}-{3:3}, at: process_output_block drivers/tty/n_tty.c:550 [inline]
 #3: ffffc90000fd0378 (&ldata->output_lock){+.+.}-{3:3}, at: n_tty_write+0x613/0x1170 drivers/tty/n_tty.c:2333
2 locks held by syz-executor.2/17020:
1 lock held by syz-executor.2/17052:
 #0: ffff8880a3453078 (&fb_info->lock){+.+.}-{3:3}, at: lock_fb_info include/linux/fb.h:637 [inline]
 #0: ffff8880a3453078 (&fb_info->lock){+.+.}-{3:3}, at: fb_open+0x14b/0x3b0 drivers/video/fbdev/core/fbmem.c:1418

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

NMI backtrace for cpu 1
CPU: 1 PID: 1136 Comm: khungtaskd Not tainted 5.7.0-rc1-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+0x1e9/0x30e lib/dump_stack.c:118
 nmi_cpu_backtrace+0x9f/0x180 lib/nmi_backtrace.c:101
 arch_trigger_cpumask_backtrace+0x10/0x10 arch/x86/kernel/apic/hw_nmi.c:38
 nmi_trigger_cpumask_backtrace+0x16a/0x280 lib/nmi_backtrace.c:62
 check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
 watchdog+0xd2a/0xd40 kernel/hung_task.c:289
 kthread+0x353/0x380 kernel/kthread.c:268
 hungtask_pm_notify+0x50/0x50 kernel/hung_task.c:265
 kthread_blkcg+0xd0/0xd0 kernel/kthread.c:1247
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 17020 Comm: syz-executor.2 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__sanitizer_cov_trace_pc+0x35/0x50 kernel/kcov.c:193
Code: 02 00 65 8b 15 68 bb 8e 7e f7 c2 00 01 1f 00 75 2c 8b 91 d8 13 00 00 83 fa 02 75 21 48 8b 91 e0 13 00 00 48 8b 32 48 8d 7e 01 <8b> 89 dc 13 00 00 48 39 cf 73 08 48 89 44 f2 08 48 89 3a c3 0f 1f
RSP: 0018:ffffc9001606f950 EFLAGS: 00000246
RAX: ffffffff83d17b40 RBX: 0000000000000000 RCX: ffff8880531441c0
RDX: ffffc9000d3b3000 RSI: 000000000003ffff RDI: 0000000000040000
RBP: 0000000000000007 R08: ffffffff83d17afb R09: ffffffff83d1726f
R10: ffff8880531441c0 R11: 0000000000000002 R12: 00000000299b78fb
R13: ffff8880000a0005 R14: fffffffffffffff4 R15: 000000000000000b
FS:  00007eff34b83700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c015485008 CR3: 00000000932d8000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 vga16fb_fillrect+0xfe0/0x13e0 drivers/video/fbdev/vga16fb.c:922
 bit_clear_margins+0x37b/0x620 drivers/video/fbdev/core/bitblit.c:232
 fbcon_clear_margins drivers/video/fbdev/core/fbcon.c:1381 [inline]
 fbcon_switch+0x1448/0x1e40 drivers/video/fbdev/core/fbcon.c:2363
 redraw_screen+0x4fc/0x16f0 drivers/tty/vt/vt.c:1009
 fbcon_modechanged+0x8d5/0xd90 drivers/video/fbdev/core/fbcon.c:3000
 fb_set_var+0x822/0xcc0 drivers/video/fbdev/core/fbmem.c:1056
 do_fb_ioctl+0x502/0x6f0 drivers/video/fbdev/core/fbmem.c:1109
 fb_write+0x540/0x540 drivers/video/fbdev/core/fbmem.c:849
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl fs/ioctl.c:763 [inline]
 __do_sys_ioctl fs/ioctl.c:772 [inline]
 __se_sys_ioctl+0xf9/0x160 fs/ioctl.c:770
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x45c889
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007eff34b82c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007eff34b836d4 RCX: 000000000045c889
RDX: 0000000020000000 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000002f0 R14: 00000000004c54e4 R15: 000000000076bf0c

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2020/04/14 21:57 upstream 8632e9b5645b 3f3c5574 .config console log report ci-upstream-kasan-gce-smack-root
* Struck through repros no longer work on HEAD.