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Subjectpossible deadlock in console_unlock
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Hello,

syzbot found the following crash on:

HEAD commit: af6c5d5e01ad Merge branch 'for-4.18' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=173d93ef800000
kernel config: https://syzkaller.appspot.com/x/.config?x=12ff770540994680
dashboard link: https://syzkaller.appspot.com/bug?extid=43e93968b964e369db0b
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=16e00bb7800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+43e93968b964e369db0b@syzkaller.appspotmail.com

RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

======================================================
WARNING: possible circular locking dependency detected
4.17.0+ #111 Not tainted
------------------------------------------------------
syz-executor0/4774 is trying to acquire lock:
(ptrval) (console_owner){-...}, at: log_next
kernel/printk/printk.c:496 [inline]
(ptrval) (console_owner){-...}, at: console_unlock+0x583/0x1100
kernel/printk/printk.c:2382

but task is already holding lock:
(ptrval) (&(&port->lock)->rlock){-.-.}, at: pty_write+0xf9/0x1f0
drivers/tty/pty.c:119

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&(&port->lock)->rlock){-.-.}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x96/0xc0 kernel/locking/spinlock.c:152
tty_port_tty_get+0x20/0x80 drivers/tty/tty_port.c:288
tty_port_default_wakeup+0x15/0x40 drivers/tty/tty_port.c:47
tty_port_tty_wakeup+0x5d/0x70 drivers/tty/tty_port.c:390
uart_write_wakeup+0x44/0x60 drivers/tty/serial/serial_core.c:103
serial8250_tx_chars+0x4be/0xb60
drivers/tty/serial/8250/8250_port.c:1808
serial8250_handle_irq.part.25+0x1ee/0x280
drivers/tty/serial/8250/8250_port.c:1881
serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1867
[inline]
serial8250_default_handle_irq+0xc8/0x150
drivers/tty/serial/8250/8250_port.c:1897
serial8250_interrupt+0xfa/0x1d0
drivers/tty/serial/8250/8250_core.c:125
__handle_irq_event_percpu+0x1c0/0xad0 kernel/irq/handle.c:149
handle_irq_event_percpu+0x98/0x1c0 kernel/irq/handle.c:189
handle_irq_event+0xa7/0x135 kernel/irq/handle.c:206
handle_edge_irq+0x20f/0x870 kernel/irq/chip.c:791
generic_handle_irq_desc include/linux/irqdesc.h:159 [inline]
handle_irq+0x18c/0x2e7 arch/x86/kernel/irq_64.c:77
do_IRQ+0x78/0x190 arch/x86/kernel/irq.c:245
ret_from_intr+0x0/0x1e
native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54
arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
default_idle+0xc2/0x440 arch/x86/kernel/process.c:500
arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:491
default_idle_call+0x6d/0x90 kernel/sched/idle.c:93
cpuidle_idle_call kernel/sched/idle.c:153 [inline]
do_idle+0x395/0x560 kernel/sched/idle.c:262
cpu_startup_entry+0x104/0x120 kernel/sched/idle.c:368
start_secondary+0x42b/0x5c0 arch/x86/kernel/smpboot.c:265
secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:242

-> #1 (&port_lock_key){-.-.}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x96/0xc0 kernel/locking/spinlock.c:152
serial8250_console_write+0x8d5/0xb00
drivers/tty/serial/8250/8250_port.c:3230
univ8250_console_write+0x5f/0x70
drivers/tty/serial/8250/8250_core.c:590
call_console_drivers kernel/printk/printk.c:1718 [inline]
console_unlock+0xac2/0x1100 kernel/printk/printk.c:2395
vprintk_emit+0x6ad/0xdd0 kernel/printk/printk.c:1907
vprintk_default+0x28/0x30 kernel/printk/printk.c:1947
vprintk_func+0x7a/0xe7 kernel/printk/printk_safe.c:379
printk+0x9e/0xba kernel/printk/printk.c:1980
register_console+0x7e7/0xc00 kernel/printk/printk.c:2714
univ8250_console_init+0x3f/0x4b
drivers/tty/serial/8250/8250_core.c:685
console_init+0x6d9/0xa38 kernel/printk/printk.c:2798
start_kernel+0x608/0x92d init/main.c:661
x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:452
x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:433
secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:242

-> #0 (console_owner){-...}:
lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3924
console_lock_spinning_enable kernel/printk/printk.c:1581 [inline]
console_unlock+0x5ef/0x1100 kernel/printk/printk.c:2392
vprintk_emit+0x6ad/0xdd0 kernel/printk/printk.c:1907
vprintk_default+0x28/0x30 kernel/printk/printk.c:1947
vprintk_func+0x7a/0xe7 kernel/printk/printk_safe.c:379
printk+0x9e/0xba kernel/printk/printk.c:1980
fail_dump lib/fault-inject.c:44 [inline]
should_fail+0x97a/0xbcd lib/fault-inject.c:149
__should_failslab+0x124/0x180 mm/failslab.c:32
should_failslab+0x9/0x14 mm/slab_common.c:1522
slab_pre_alloc_hook mm/slab.h:423 [inline]
slab_alloc mm/slab.c:3378 [inline]
__do_kmalloc mm/slab.c:3716 [inline]
__kmalloc+0x63/0x760 mm/slab.c:3727
kmalloc include/linux/slab.h:517 [inline]
tty_buffer_alloc drivers/tty/tty_buffer.c:170 [inline]
__tty_buffer_request_room+0x2d2/0x7f0 drivers/tty/tty_buffer.c:268
tty_insert_flip_string_fixed_flag+0x8d/0x1f0
drivers/tty/tty_buffer.c:313
tty_insert_flip_string include/linux/tty_flip.h:37 [inline]
pty_write+0x12c/0x1f0 drivers/tty/pty.c:121
tty_put_char+0x129/0x150 drivers/tty/tty_io.c:2865
__process_echoes+0x4d9/0x8d0 drivers/tty/n_tty.c:703
process_echoes+0xfc/0x170 drivers/tty/n_tty.c:781
n_tty_set_termios+0xb56/0xe80 drivers/tty/n_tty.c:1837
tty_set_termios+0x7a0/0xac0 drivers/tty/tty_ioctl.c:341
set_termios+0x41e/0x7d0 drivers/tty/tty_ioctl.c:414
tty_mode_ioctl+0x871/0xb50 drivers/tty/tty_ioctl.c:781
n_tty_ioctl_helper+0x54/0x3b0 drivers/tty/tty_ioctl.c:940
n_tty_ioctl+0x54/0x320 drivers/tty/n_tty.c:2441
tty_ioctl+0x5e1/0x1870 drivers/tty/tty_io.c:2655
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1cf/0x16f0 fs/ioctl.c:684
__do_compat_sys_ioctl fs/compat_ioctl.c:1483 [inline]
__se_compat_sys_ioctl fs/compat_ioctl.c:1407 [inline]
__ia32_compat_sys_ioctl+0x43e/0x640 fs/compat_ioctl.c:1407
do_syscall_32_irqs_on arch/x86/entry/common.c:323 [inline]
do_fast_syscall_32+0x345/0xf9b arch/x86/entry/common.c:394
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

other info that might help us debug this:

Chain exists of:
console_owner --> &port_lock_key --> &(&port->lock)->rlock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&(&port->lock)->rlock);
lock(&port_lock_key);
lock(&(&port->lock)->rlock);
lock(console_owner);

*** DEADLOCK ***

6 locks held by syz-executor0/4774:
#0: (ptrval) (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (ptrval) (&o_tty->termios_rwsem/1){++++}, at:
tty_set_termios+0xfd/0xac0 drivers/tty/tty_ioctl.c:328
#2: (ptrval) (&tty->ldisc_sem){++++}, at: tty_ldisc_ref+0x22/0x90
drivers/tty/tty_ldisc.c:284
#3: (ptrval) (&ldata->output_lock){+.+.}, at:
process_echoes+0xb6/0x170 drivers/tty/n_tty.c:779
#4: (ptrval) (&(&port->lock)->rlock){-.-.}, at:
pty_write+0xf9/0x1f0 drivers/tty/pty.c:119
#5: (ptrval) (console_lock){+.+.}, at: console_trylock_spinning
kernel/printk/printk.c:1643 [inline]
#5: (ptrval) (console_lock){+.+.}, at: vprintk_emit+0x694/0xdd0
kernel/printk/printk.c:1906

stack backtrace:
CPU: 1 PID: 4774 Comm: syz-executor0 Not tainted 4.17.0+ #111
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+0x1b9/0x294 lib/dump_stack.c:113
print_circular_bug.isra.36.cold.56+0x1bd/0x27d
kernel/locking/lockdep.c:1227
check_prev_add kernel/locking/lockdep.c:1867 [inline]
check_prevs_add kernel/locking/lockdep.c:1980 [inline]
validate_chain kernel/locking/lockdep.c:2421 [inline]
__lock_acquire+0x343e/0x5140 kernel/locking/lockdep.c:3435
lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3924
console_lock_spinning_enable kernel/printk/printk.c:1581 [inline]
console_unlock+0x5ef/0x1100 kernel/printk/printk.c:2392
vprintk_emit+0x6ad/0xdd0 kernel/printk/printk.c:1907
vprintk_default+0x28/0x30 kernel/printk/printk.c:1947
vprintk_func+0x7a/0xe7 kernel/printk/printk_safe.c:379
printk+0x9e/0xba kernel/printk/printk.c:1980
fail_dump lib/fault-inject.c:44 [inline]
should_fail+0x97a/0xbcd lib/fault-inject.c:149
__should_failslab+0x124/0x180 mm/failslab.c:32
should_failslab+0x9/0x14 mm/slab_common.c:1522
slab_pre_alloc_hook mm/slab.h:423 [inline]
slab_alloc mm/slab.c:3378 [inline]
__do_kmalloc mm/slab.c:3716 [inline]
__kmalloc+0x63/0x760 mm/slab.c:3727
kmalloc include/linux/slab.h:517 [inline]
tty_buffer_alloc drivers/tty/tty_buffer.c:170 [inline]
__tty_buffer_request_room+0x2d2/0x7f0 drivers/tty/tty_buffer.c:268
tty_insert_flip_string_fixed_flag+0x8d/0x1f0 drivers/tty/tty_buffer.c:313
tty_insert_flip_string include/linux/tty_flip.h:37 [inline]
pty_write+0x12c/0x1f0 drivers/tty/pty.c:121
tty_put_char+0x129/0x150 drivers/tty/tty_io.c:2865
__process_echoes+0x4d9/0x8d0 drivers/tty/n_tty.c:703
process_echoes+0xfc/0x170 drivers/tty/n_tty.c:781
n_tty_set_termios+0xb56/0xe80 drivers/tty/n_tty.c:1837
tty_set_termios+0x7a0/0xac0 drivers/tty/tty_ioctl.c:341
set_termios+0x41e/0x7d0 drivers/tty/tty_ioctl.c:414
tty_mode_ioctl+0x871/0xb50 drivers/tty/tty_ioctl.c:781
n_tty_ioctl_helper+0x54/0x3b0 drivers/tty/tty_ioctl.c:940
n_tty_ioctl+0x54/0x320 drivers/tty/n_tty.c:2441
tty_ioctl+0x5e1/0x1870 drivers/tty/tty_io.c:2655
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1cf/0x16f0 fs/ioctl.c:684
__do_compat_sys_ioctl fs/compat_ioctl.c:1483 [inline]
__se_compat_sys_ioctl fs/compat_ioctl.c:1407 [inline]
__ia32_compat_sys_ioctl+0x43e/0x640 fs/compat_ioctl.c:1407


---
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 syzkaller@googlegroups.com.

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

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