INFO: task hung in fb_open

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: fbc5fe7a Linux 4.14.157
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13921b7ae00000
kernel config: https://syzkaller.appspot.com/x/.config?x=d49d9f4045dcfa5d
dashboard link: https://syzkaller.appspot.com/bug?extid=49e4beaefa2981579752
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1171fc32e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1520781ee00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+49e4be...@syzkaller.appspotmail.com

audit: type=1400 audit(1575360785.721:36): avc: denied { map } for
pid=6986 comm="syz-executor833" path="/root/syz-executor833830099"
dev="sda1" ino=1426 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
INFO: task syz-executor833:6988 blocked for more than 140 seconds.
Not tainted 4.14.157-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor833 D28904 6988 6984 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
schedule+0x92/0x1c0 kernel/sched/core.c:3428
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x73c/0x1470 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
fb_open+0xb7/0x420 drivers/video/fbdev/core/fbmem.c:1468
chrdev_open+0x207/0x590 fs/char_dev.c:423
do_dentry_open+0x73b/0xeb0 fs/open.c:777
vfs_open+0x105/0x220 fs/open.c:891
do_last fs/namei.c:3425 [inline]
path_openat+0x8bd/0x3f70 fs/namei.c:3566
do_filp_open+0x18e/0x250 fs/namei.c:3600
do_sys_open+0x2c5/0x430 fs/open.c:1084
SYSC_openat fs/open.c:1111 [inline]
SyS_openat+0x30/0x40 fs/open.c:1105
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x445979
RSP: 002b:00007fdb83cc7db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00000000006dac38 RCX: 0000000000445979
RDX: 0000000000000000 RSI: 0000000020000280 RDI: ffffffffffffff9c
RBP: 00000000006dac30 R08: 00007fdb83cc8700 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac3c
R13: 00007ffed720031f R14: 00007fdb83cc89c0 R15: 20c49ba5e353f7cf
INFO: task syz-executor833:6989 blocked for more than 140 seconds.
Not tainted 4.14.157-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor833 D29664 6989 6984 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
schedule+0x92/0x1c0 kernel/sched/core.c:3428
schedule_timeout+0x93b/0xe10 kernel/time/timer.c:1723
__down_common kernel/locking/semaphore.c:221 [inline]
__down+0x160/0x290 kernel/locking/semaphore.c:238
down+0x64/0x90 kernel/locking/semaphore.c:62
console_lock+0x28/0x80 kernel/printk/printk.c:2216
do_fb_ioctl+0x36a/0x940 drivers/video/fbdev/core/fbmem.c:1121
fb_ioctl+0xe6/0x130 drivers/video/fbdev/core/fbmem.c:1242
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x445979
RSP: 002b:00007fdb83ca6db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dac48 RCX: 0000000000445979
RDX: 00000000200003c0 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 00000000006dac40 R08: 00007fdb83ca7700 R09: 0000000000000000
R10: 00007fdb83ca7700 R11: 0000000000000246 R12: 00000000006dac4c
R13: 00007ffed720031f R14: 00007fdb83ca79c0 R15: 20c49ba5e353f7cf

Showing all locks held in the system:
1 lock held by khungtaskd/1042:
#0: (tasklist_lock){.+.+}, at: [<ffffffff8148a428>]
debug_show_all_locks+0x7f/0x21f kernel/locking/lockdep.c:4544
1 lock held by rsyslogd/6840:
#0: (&f->f_pos_lock){+.+.}, at: [<ffffffff8196407b>]
__fdget_pos+0xab/0xd0 fs/file.c:769
2 locks held by getty/6963:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff86614193>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff8348e086>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6964:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff86614193>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff8348e086>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6965:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff86614193>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff8348e086>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6966:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff86614193>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff8348e086>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6967:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff86614193>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff8348e086>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6968:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff86614193>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff8348e086>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6969:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff86614193>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff8348e086>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
1 lock held by syz-executor833/6988:
#0: (&fb_info->lock){+.+.}, at: [<ffffffff83246fd7>] fb_open+0xb7/0x420
drivers/video/fbdev/core/fbmem.c:1468

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

NMI backtrace for cpu 1
CPU: 1 PID: 1042 Comm: khungtaskd Not tainted 4.14.157-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x142/0x197 lib/dump_stack.c:58
nmi_cpu_backtrace.cold+0x57/0x94 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x141/0x189 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:140 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
watchdog+0x5e7/0xb90 kernel/hung_task.c:274
kthread+0x319/0x430 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 6987 Comm: syz-executor833 Not tainted 4.14.157-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
task: ffff888091f26640 task.stack: ffff88808bd48000
RIP: 0010:__writeq arch/x86/include/asm/io.h:100 [inline]
RIP: 0010:bitfill_aligned drivers/video/fbdev/core/cfbfillrect.c:64 [inline]
RIP: 0010:bitfill_aligned+0xdc/0x190
drivers/video/fbdev/core/cfbfillrect.c:35
RSP: 0018:ffff88808bd4f270 EFLAGS: 00000297
RAX: ffff888091f26640 RBX: 0000000000000050 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff8880000a0000 RDI: 0000000000000040
RBP: ffff88808bd4f2a8 R08: 0000000000001400 R09: 0000000000000040
R10: ffffed104323b3b3 R11: ffff8882191d9d9f R12: ffff8880000a0280
R13: 0000000000000000 R14: ffff8880000a0140 R15: 0000000000000000
FS: 00007fdb83ce9700(0000) GS:ffff8880aec00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fdb83ca6e78 CR3: 00000000a0858000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
cfb_fillrect+0x3d0/0x720 drivers/video/fbdev/core/cfbfillrect.c:327
vga16fb_fillrect+0x618/0x1880 drivers/video/fbdev/vga16fb.c:951
bit_clear_margins+0x2d5/0x4f0 drivers/video/fbdev/core/bitblit.c:232
fbcon_clear_margins+0x292/0x320 drivers/video/fbdev/core/fbcon.c:1317
fbcon_switch+0xd38/0x1820 drivers/video/fbdev/core/fbcon.c:2299
redraw_screen+0x335/0x7c0 drivers/tty/vt/vt.c:688
fbcon_modechanged+0x59e/0x880 drivers/video/fbdev/core/fbcon.c:2946
fbcon_event_notify+0x11f/0x17af drivers/video/fbdev/core/fbcon.c:3299
notifier_call_chain+0x111/0x1b0 kernel/notifier.c:93
__blocking_notifier_call_chain kernel/notifier.c:317 [inline]
__blocking_notifier_call_chain kernel/notifier.c:304 [inline]
blocking_notifier_call_chain kernel/notifier.c:328 [inline]
blocking_notifier_call_chain+0x80/0xa0 kernel/notifier.c:325
fb_notifier_call_chain+0x25/0x30 drivers/video/fbdev/core/fb_notify.c:45
fb_set_var+0xb09/0xcf0 drivers/video/fbdev/core/fbmem.c:1054
do_fb_ioctl+0x3cc/0x940 drivers/video/fbdev/core/fbmem.c:1127
fb_ioctl+0xe6/0x130 drivers/video/fbdev/core/fbmem.c:1242
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x445979
RSP: 002b:00007fdb83ce8db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dac28 RCX: 0000000000445979
RDX: 00000000200003c0 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac2c
R13: 00007ffed720031f R14: 00007fdb83ce99c0 R15: 20c49ba5e353f7cf
Code: 34 fe 89 d8 31 d2 f7 75 d4 83 f8 07 89 c3 41 89 c4 76 49 44 8d 60 f8
41 c1 ec 03 49 83 c4 01 49 c1 e4 06 4d 01 f4 e8 d4 ac 34 fe <4d> 89 3e 4d
89 7e 08 4d 89 7e 10 4d 89 7e 18 4d 89 7e 20 4d 89


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this bug, for details see:
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[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 174651bd Linux 4.19.87
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12cdd196e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c8b1666d827aa49d
dashboard link: https://syzkaller.appspot.com/bug?extid=bbf1fc109bb816889956

compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:

Reported-by: syzbot+bbf1fc...@syzkaller.appspotmail.com

kobject: 'loop1' (00000000d2e0e8ee): kobject_uevent_env
kobject: 'loop1' (00000000d2e0e8ee): fill_kobj_path: path
= '/devices/virtual/block/loop1'
kobject: 'loop3' (000000004e97f472): kobject_uevent_env
kobject: 'loop3' (000000004e97f472): fill_kobj_path: path
= '/devices/virtual/block/loop3'
audit: type=1400 audit(1575458221.953:87): avc: denied { map } for
pid=10773 comm="sh" path="/bin/dash" dev="sda1" ino=1473
scontext=system_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=system_u:object_r:file_t:s0 tclass=file permissive=1
INFO: task syz-executor.4:10752 blocked for more than 140 seconds.
Not tainted 4.19.87-syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor.4 D29224 10752 7937 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2826 [inline]
__schedule+0x866/0x1dc0 kernel/sched/core.c:3515
schedule+0x92/0x1c0 kernel/sched/core.c:3559
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3617
__mutex_lock_common kernel/locking/mutex.c:1002 [inline]
__mutex_lock+0x726/0x1300 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
fb_open+0xd7/0x450 drivers/video/fbdev/core/fbmem.c:1457
chrdev_open+0x245/0x6b0 fs/char_dev.c:423
do_dentry_open+0x4c3/0x1210 fs/open.c:796
vfs_open+0xa0/0xd0 fs/open.c:905
do_last fs/namei.c:3418 [inline]
path_openat+0x10d7/0x45e0 fs/namei.c:3534
do_filp_open+0x1a1/0x280 fs/namei.c:3564
do_sys_open+0x3fe/0x550 fs/open.c:1088
__do_sys_openat fs/open.c:1115 [inline]
__se_sys_openat fs/open.c:1109 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1109
do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a679
Code: f3 44 0f 6f 74 1e e0 f3 44 0f 6f 7c 1e f0 f3 0f 7f 07 f3 0f 7f 4f 10
f3 0f 7f 57 20 f3 0f 7f 5f 30 f3 0f 7f 67 40 f3 0f 7f 6f <50> f3 0f 7f 77
60 f3 0f 7f 7f 70 f3 44 0f 7f 44 1f 80 f3 44 0f 7f
RSP: 002b:00007f19ad31bc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 000000000045a679
RDX: 0000000000000000 RSI: 0000000020000100 RDI: ffffffffffffff9c
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f19ad31c6d4
R13: 00000000004c7d42 R14: 00000000004dee48 R15: 00000000ffffffff
INFO: task syz-executor.5:10705 blocked for more than 140 seconds.
Not tainted 4.19.87-syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor.5 D29224 10705 7942 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2826 [inline]
__schedule+0x866/0x1dc0 kernel/sched/core.c:3515
schedule+0x92/0x1c0 kernel/sched/core.c:3559
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3617
__mutex_lock_common kernel/locking/mutex.c:1002 [inline]
__mutex_lock+0x726/0x1300 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
fb_open+0xd7/0x450 drivers/video/fbdev/core/fbmem.c:1457
chrdev_open+0x245/0x6b0 fs/char_dev.c:423
do_dentry_open+0x4c3/0x1210 fs/open.c:796
vfs_open+0xa0/0xd0 fs/open.c:905
do_last fs/namei.c:3418 [inline]
path_openat+0x10d7/0x45e0 fs/namei.c:3534
do_filp_open+0x1a1/0x280 fs/namei.c:3564
do_sys_open+0x3fe/0x550 fs/open.c:1088
__do_sys_openat fs/open.c:1115 [inline]
__se_sys_openat fs/open.c:1109 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1109
do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a679
Code: f3 44 0f 6f 74 1e e0 f3 44 0f 6f 7c 1e f0 f3 0f 7f 07 f3 0f 7f 4f 10
f3 0f 7f 57 20 f3 0f 7f 5f 30 f3 0f 7f 67 40 f3 0f 7f 6f <50> f3 0f 7f 77
60 f3 0f 7f 7f 70 f3 44 0f 7f 44 1f 80 f3 44 0f 7f
RSP: 002b:00007f5e20d4dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 000000000045a679
RDX: 0000000000000000 RSI: 0000000020000100 RDI: ffffffffffffff9c
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5e20d4e6d4
R13: 00000000004c7d42 R14: 00000000004dee48 R15: 00000000ffffffff
INFO: task syz-executor.5:10709 blocked for more than 140 seconds.
Not tainted 4.19.87-syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor.5 D29224 10709 7942 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2826 [inline]
__schedule+0x866/0x1dc0 kernel/sched/core.c:3515
schedule+0x92/0x1c0 kernel/sched/core.c:3559
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3617
__mutex_lock_common kernel/locking/mutex.c:1002 [inline]
__mutex_lock+0x726/0x1300 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
fb_open+0xd7/0x450 drivers/video/fbdev/core/fbmem.c:1457
chrdev_open+0x245/0x6b0 fs/char_dev.c:423
do_dentry_open+0x4c3/0x1210 fs/open.c:796
vfs_open+0xa0/0xd0 fs/open.c:905
do_last fs/namei.c:3418 [inline]
path_openat+0x10d7/0x45e0 fs/namei.c:3534
do_filp_open+0x1a1/0x280 fs/namei.c:3564
do_sys_open+0x3fe/0x550 fs/open.c:1088
__do_sys_openat fs/open.c:1115 [inline]
__se_sys_openat fs/open.c:1109 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1109
do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a679
Code: f3 44 0f 6f 74 1e e0 f3 44 0f 6f 7c 1e f0 f3 0f 7f 07 f3 0f 7f 4f 10
f3 0f 7f 57 20 f3 0f 7f 5f 30 f3 0f 7f 67 40 f3 0f 7f 6f <50> f3 0f 7f 77
60 f3 0f 7f 7f 70 f3 44 0f 7f 44 1f 80 f3 44 0f 7f
RSP: 002b:00007f5e20d2cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 000000000045a679
RDX: 0000000000000000 RSI: 0000000020000100 RDI: ffffffffffffff9c
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5e20d2d6d4
R13: 00000000004c7d42 R14: 00000000004dee48 R15: 00000000ffffffff

Showing all locks held in the system:

1 lock held by khungtaskd/1068:
#0: 0000000089402ee8 (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x27e kernel/locking/lockdep.c:4438
1 lock held by rsyslogd/7765:
#0: 00000000d45aed95 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110
fs/file.c:767
2 locks held by getty/7887:
#0: 00000000783d488d (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000871f4b1a (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b30 drivers/tty/n_tty.c:2154
2 locks held by getty/7888:
#0: 00000000b05af4a1 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 000000003739c765 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b30 drivers/tty/n_tty.c:2154
2 locks held by getty/7889:
#0: 000000000bbc6441 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000399e9331 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b30 drivers/tty/n_tty.c:2154
2 locks held by getty/7890:
#0: 00000000ba11aa8b (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000d8c10e4d (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b30 drivers/tty/n_tty.c:2154
2 locks held by getty/7891:
#0: 000000007abfb31c (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000a6442331 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b30 drivers/tty/n_tty.c:2154
2 locks held by getty/7892:
#0: 000000005ef19dd7 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000f8d3bac0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b30 drivers/tty/n_tty.c:2154
2 locks held by getty/7893:
#0: 000000009a807b79 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000e3bbcbbd (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b30 drivers/tty/n_tty.c:2154
3 locks held by syz-executor.4/10697:
1 lock held by syz-executor.4/10752:
#0: 00000000cdc8bb80 (&fb_info->lock){+.+.}, at: fb_open+0xd7/0x450
drivers/video/fbdev/core/fbmem.c:1457
1 lock held by syz-executor.5/10705:
#0: 00000000cdc8bb80 (&fb_info->lock){+.+.}, at: fb_open+0xd7/0x450
drivers/video/fbdev/core/fbmem.c:1457
1 lock held by syz-executor.5/10709:
#0: 00000000cdc8bb80 (&fb_info->lock){+.+.}, at: fb_open+0xd7/0x450
drivers/video/fbdev/core/fbmem.c:1457

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

NMI backtrace for cpu 1

CPU: 1 PID: 1068 Comm: khungtaskd Not tainted 4.19.87-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+0x197/0x210 lib/dump_stack.c:118
nmi_cpu_backtrace.cold+0x63/0xa4 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1b0/0x1f8 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+0x9df/0xee0 kernel/hung_task.c:287
kthread+0x354/0x420 kernel/kthread.c:246
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0

CPU: 0 PID: 10697 Comm: syz-executor.4 Not tainted 4.19.87-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011

RIP: 0010:__sanitizer_cov_trace_pc+0x3b/0x50 kernel/kcov.c:106
Code: 65 8b 15 78 d9 96 7e 81 e2 00 01 1f 00 75 2b 8b 90 d0 12 00 00 83 fa
02 75 20 48 8b 88 d8 12 00 00 8b 80 d4 12 00 00 48 8b 11 <48> 83 c2 01 48
39 d0 76 07 48 89 34 d1 48 89 11 5d c3 0f 1f 00 65
RSP: 0018:ffff88804719f150 EFLAGS: 00000246
RAX: 0000000000040000 RBX: 0000000000000000 RCX: ffffc9000e69e000
RDX: 000000000003ffff RSI: ffffffff83834999 RDI: 0000000000000005
RBP: ffff88804719f150 R08: ffff888095b264c0 R09: 0000000000000040
R10: ffffed10432ccd13 R11: ffff88821966689f R12: 0000000000000040
R13: 0000000000000040 R14: ffff8880000a0000 R15: 0000000000000000
FS: 00007f19ad33d700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: ffffffffff600400 CR3: 00000000470a8000 CR4: 00000000001406f0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:

bitfill_aligned drivers/video/fbdev/core/cfbfillrect.c:43 [inline]
bitfill_aligned+0x39/0x210 drivers/video/fbdev/core/cfbfillrect.c:35
cfb_fillrect+0x423/0x7c0 drivers/video/fbdev/core/cfbfillrect.c:327
vga16fb_fillrect+0x6ce/0x19b0 drivers/video/fbdev/vga16fb.c:951
bit_clear_margins+0x30b/0x530 drivers/video/fbdev/core/bitblit.c:232
fbcon_clear_margins+0x2e3/0x370 drivers/video/fbdev/core/fbcon.c:1339
fbcon_switch+0xe7d/0x1a40 drivers/video/fbdev/core/fbcon.c:2321
redraw_screen+0x37d/0x8e0 drivers/tty/vt/vt.c:997
fbcon_modechanged+0x5f3/0x900 drivers/video/fbdev/core/fbcon.c:2969
fbcon_event_notify+0x1bd/0x1dba drivers/video/fbdev/core/fbcon.c:3344
notifier_call_chain+0xc2/0x230 kernel/notifier.c:93

__blocking_notifier_call_chain kernel/notifier.c:317 [inline]
__blocking_notifier_call_chain kernel/notifier.c:304 [inline]
blocking_notifier_call_chain kernel/notifier.c:328 [inline]

blocking_notifier_call_chain+0x94/0xb0 kernel/notifier.c:325
fb_notifier_call_chain+0x25/0x30 drivers/video/fbdev/core/fb_notify.c:45
fb_set_var+0xc8f/0xe80 drivers/video/fbdev/core/fbmem.c:1042
do_fb_ioctl+0x450/0xab0 drivers/video/fbdev/core/fbmem.c:1115
fb_ioctl+0xe6/0x130 drivers/video/fbdev/core/fbmem.c:1230
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:501 [inline]
do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:688
ksys_ioctl+0xab/0xd0 fs/ioctl.c:705
__do_sys_ioctl fs/ioctl.c:712 [inline]
__se_sys_ioctl fs/ioctl.c:710 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:710
do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a679
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:00007f19ad33cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a679
RDX: 0000000020000200 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f19ad33d6d4
R13: 00000000004c2e77 R14: 00000000004d8098 R15: 00000000ffffffff

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.