INFO: task hung in release_tty

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 84920cc7 Linux 4.19.121
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=144b7ecc100000
kernel config: https://syzkaller.appspot.com/x/.config?x=1deab1e33c1e397b
dashboard link: https://syzkaller.appspot.com/bug?extid=ba9987baa715ce3b6abf
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+ba9987...@syzkaller.appspotmail.com

base_sock_release(00000000528b61ac) sk=000000003caa62eb
caif:caif_disconnect_client(): nothing to disconnect
caif:caif_disconnect_client(): nothing to disconnect
caif:caif_disconnect_client(): nothing to disconnect
caif:caif_disconnect_client(): nothing to disconnect
INFO: task syz-executor.4:27534 blocked for more than 140 seconds.
Not tainted 4.19.121-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.4 D26880 27534 6794 0x80000002
Call Trace:
schedule+0x8d/0x1b0 kernel/sched/core.c:3559
schedule_timeout+0x896/0xf20 kernel/time/timer.c:1782
__down_common kernel/locking/semaphore.c:221 [inline]
__down+0x176/0x2c0 kernel/locking/semaphore.c:238
down+0x57/0x80 kernel/locking/semaphore.c:62
console_lock+0x25/0x80 kernel/printk/printk.c:2244
con_shutdown+0x3d/0x90 drivers/tty/vt/vt.c:3276
release_tty+0xda/0x4c0 drivers/tty/tty_io.c:1509
tty_release_struct+0x37/0x50 drivers/tty/tty_io.c:1624
tty_release+0xbc7/0xe90 drivers/tty/tty_io.c:1784
__fput+0x2cd/0x890 fs/file_table.c:278
task_work_run+0x13f/0x1b0 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0xbcd/0x2f30 kernel/exit.c:880
do_group_exit+0x125/0x350 kernel/exit.c:983
get_signal+0x3ec/0x1f90 kernel/signal.c:2588
do_signal+0x8f/0x1710 arch/x86/kernel/signal.c:821
exit_to_usermode_loop+0x22b/0x2b0 arch/x86/entry/common.c:163
prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
syscall_return_slowpath arch/x86/entry/common.c:271 [inline]
do_syscall_64+0x538/0x620 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c829
Code: 08 48 c7 44 24 10 09 00 00 00 e8 02 a1 fa ff 48 8b 44 24 18 48 8b 4c 24 30 48 83 c1 10 48 89 0c 24 48 89 44 24 08 48 c7 44 24 <10> 58 1f 00 00 e8 dd a0 fa ff 48 8b 44 24 18 48 89 44 24 40 48 8b
RSP: 002b:00007f8c69d31cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 000000000078bf08 RCX: 000000000045c829
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000078bf08
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078bf0c
R13: 00007fff27d16f8f R14: 00007f8c69d329c0 R15: 000000000078bf0c

Showing all locks held in the system:
1 lock held by khungtaskd/1075:
#0: 000000005870d5f1 (rcu_read_lock){....}, at: debug_show_all_locks+0x53/0x265 kernel/locking/lockdep.c:4440
1 lock held by in:imklog/6106:
#0: 00000000e39585ad (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xe3/0x100 fs/file.c:767
2 locks held by agetty/6141:
#0: 000000006de8fdda (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:272
#1: 00000000cb8d1b18 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x217/0x1a50 drivers/tty/n_tty.c:2154
2 locks held by agetty/6142:
#0: 00000000bbad67a7 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:272
#1: 00000000d0b7479f (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x217/0x1a50 drivers/tty/n_tty.c:2154
1 lock held by syz-executor.4/27534:
#0: 000000001e77ce4b (tty_mutex){+.+.}, at: tty_release_struct+0x2c/0x50 drivers/tty/tty_io.c:1623
1 lock held by syz-executor.4/29275:

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

NMI backtrace for cpu 0
CPU: 0 PID: 1075 Comm: khungtaskd Not tainted 4.19.121-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+0x188/0x20d lib/dump_stack.c:118
nmi_cpu_backtrace.cold+0x63/0xa2 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1a6/0x1eb 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+0x962/0xe40 kernel/hung_task.c:287
kthread+0x34a/0x420 kernel/kthread.c:246
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: 29275 Comm: syz-executor.4 Not tainted 4.19.121-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__sanitizer_cov_trace_cmp4+0x4/0x20 kernel/kcov.c:162
Code: b6 f7 31 ff eb 80 48 8b 0c 24 0f b7 d6 0f b7 f7 bf 02 00 00 00 e9 6c ff ff ff 66 90 66 2e 0f 1f 84 00 00 00 00 00 48 8b 0c 24 <89> f2 89 fe bf 04 00 00 00 e9 4e ff ff ff 0f 1f 40 00 66 2e 0f 1f
RSP: 0018:ffff888212f574f8 EFLAGS: 00000286
RAX: 0000000000040000 RBX: 0000000000000050 RCX: ffffffff837b76ea
RDX: 0000000000040000 RSI: 0000000000000014 RDI: 0000000000000050
RBP: 0000000000000014 R08: ffff88808cc5c640 R09: ffffed1014bbcbe4
R10: ffffed1014bbcbe3 R11: ffff8880a5de5f1f R12: ffff8880000a0014
R13: ffff8880000a0000 R14: 0000000000000000 R15: 00000000e7bd3887
FS: 00007f8c69d11700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f66496cd000 CR3: 000000008268e000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
vga16fb_fillrect+0x9da/0x1960 drivers/video/fbdev/vga16fb.c:922
bit_clear_margins+0x2d5/0x4a0 drivers/video/fbdev/core/bitblit.c:232
fbcon_clear_margins+0x2d8/0x370 drivers/video/fbdev/core/fbcon.c:1342
fbcon_switch+0xe0f/0x1970 drivers/video/fbdev/core/fbcon.c:2324
redraw_screen+0x37d/0x870 drivers/tty/vt/vt.c:1010
fbcon_do_set_font+0x727/0xa30 drivers/video/fbdev/core/fbcon.c:2586
fbcon_set_font+0x733/0x870 drivers/video/fbdev/core/fbcon.c:2677
con_font_set drivers/tty/vt/vt.c:4524 [inline]
con_font_op+0xd3e/0x1130 drivers/tty/vt/vt.c:4589
vt_ioctl+0xcd0/0x2500 drivers/tty/vt/vt_ioctl.c:928
tty_ioctl+0x7a1/0x1420 drivers/tty/tty_io.c:2669
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:501 [inline]
do_vfs_ioctl+0xcda/0x12e0 fs/ioctl.c:688
ksys_ioctl+0x9b/0xc0 fs/ioctl.c:705
__do_sys_ioctl fs/ioctl.c:712 [inline]
__se_sys_ioctl fs/ioctl.c:710 [inline]
__x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:710
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c829
Code: 0d b7 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 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f8c69d10c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e9420 RCX: 000000000045c829
RDX: 0000000020000080 RSI: 0000000000004b61 RDI: 0000000000000003
RBP: 000000000078bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000421 R14: 00000000004c6c18 R15: 00007f8c69d116d4


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[syzbot]

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