Re: possible deadlock in console_unlock
From: Yao HongBo
Date: Sat Feb 16 2019 - 03:00:19 EST
On 2/16/2019 3:46 PM, Sergey Senozhatsky wrote:
> On (02/16/19 16:21), Sergey Senozhatsky wrote:
>> On (02/16/19 14:36), Yao HongBo wrote:
>>> hi, sergey:
>>>
>>> As shown in that link, https://lkml.org/lkml/2018/6/6/397
>>>
>>> On the linux kernel 5.0-rc6, Syzkaller also hit 'possible deadlock in console_unlock'
>>> bug for several times in my environment.
>>>
>>> This solution fixes things for me. Do you have a plan to submit patches to
>>> solve this problem.
>>>
>>> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
>>> __printk_safe_enter();
>>> kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
>>> __printk_safe_exit();
>>
>> I would probably try the following:
>
> Yao HongBo, could you please post the lockdep splat?
>
> GFP_NOWARN is probably the best option for now. Yes, it, maybe,
> will not work for fault-injection cases; but printk_safe approach
> is harder to push for, especially given that printk_safe maybe will
> not even exist in the future.
I have tried GFP_NOWARN, but the problem still exists.
Only print_safe contexts for tty locks can solve the problem.
My test scenario is falt-injection.
deadlock report is shown as below:
RBP: 00007f1cf76cbc70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f1cf76cc6bc
R13: 00000000004c473d R14: 0000000000701f18 R15: 0000000000000005
======================================================
WARNING: possible circular locking dependency detected
4.19.18-514.55.6.9.x86_64+ #1 Not tainted
------------------------------------------------------
syz-executor0/23291 is trying to acquire lock:
00000000d73d87c0 (console_owner){-.-.}, at: log_next kernel/printk/printk.c:495 [inline]
00000000d73d87c0 (console_owner){-.-.}, at: console_unlock+0x36d/0xb30 kernel/printk/printk.c:2397
but task is already holding lock:
00000000dfbab914 (&(&port->lock)->rlock){-.-.}, at: pty_write+0xd2/0x1d0 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){-.-.}:
tty_port_tty_get+0x20/0x80 drivers/tty/tty_port.c:288
tty_port_default_wakeup+0x16/0x40 drivers/tty/tty_port.c:47
serial8250_tx_chars+0x4dc/0xa80 drivers/tty/serial/8250/8250_port.c:1806
serial8250_handle_irq.part.12+0x198/0x220 drivers/tty/serial/8250/8250_port.c:1879
serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1899 [inline]
serial8250_default_handle_irq+0xf8/0x120 drivers/tty/serial/8250/8250_port.c:1895
serial8250_interrupt+0xfe/0x250 drivers/tty/serial/8250/8250_core.c:125
__handle_irq_event_percpu+0xf5/0x730 kernel/irq/handle.c:149
handle_irq_event_percpu+0x7b/0x170 kernel/irq/handle.c:189
handle_irq_event+0xa6/0x140 kernel/irq/handle.c:206
handle_edge_irq+0x1eb/0xa90 kernel/irq/chip.c:791
generic_handle_irq_desc include/linux/irqdesc.h:154 [inline]
handle_irq+0x3e/0x50 arch/x86/kernel/irq_64.c:78
do_IRQ+0x92/0x200 arch/x86/kernel/irq.c:246
ret_from_intr+0x0/0x22
native_safe_halt+0x2/0x10 arch/x86/include/asm/irqflags.h:57
arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
default_idle+0x24/0x2b0 arch/x86/kernel/process.c:561
cpuidle_idle_call kernel/sched/idle.c:153 [inline]
do_idle+0x2ca/0x420 kernel/sched/idle.c:262
cpu_startup_entry+0xcb/0xe0 kernel/sched/idle.c:368
start_secondary+0x421/0x570 arch/x86/kernel/smpboot.c:271
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243
-> #1 (&port_lock_key){-.-.}:
serial8250_console_write+0x68a/0x820 drivers/tty/serial/8250/8250_port.c:3247
call_console_drivers kernel/printk/printk.c:1729 [inline]
console_unlock+0x66a/0xb30 kernel/printk/printk.c:2410
vprintk_emit+0x181/0x570 kernel/printk/printk.c:1927
vprintk_default+0x68/0xe0 kernel/printk/printk.c:1968
vprintk_func+0x57/0xf0 kernel/printk/printk_safe.c:398
printk+0xb7/0xe2 kernel/printk/printk.c:2001
register_console+0x752/0xc60 kernel/printk/printk.c:2725
univ8250_console_init+0x31/0x3a drivers/tty/serial/8250/8250_core.c:685
console_init+0x3ad/0x567 kernel/printk/printk.c:2811
start_kernel+0x4c3/0x7e1 init/main.c:661
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243
-> #0 (console_owner){-.-.}:
console_lock_spinning_enable kernel/printk/printk.c:1592 [inline]
console_unlock+0x3d9/0xb30 kernel/printk/printk.c:2407
vprintk_emit+0x181/0x570 kernel/printk/printk.c:1927
vprintk_default+0x68/0xe0 kernel/printk/printk.c:1968
vprintk_func+0x57/0xf0 kernel/printk/printk_safe.c:398
printk+0xb7/0xe2 kernel/printk/printk.c:2001
fail_dump lib/fault-inject.c:44 [inline]
should_fail+0x5d3/0x700 lib/fault-inject.c:149
__should_failslab+0x110/0x180 mm/failslab.c:32
should_failslab+0xa/0x20 mm/slab_common.c:1557
slab_pre_alloc_hook mm/slab.h:423 [inline]
slab_alloc_node mm/slub.c:2632 [inline]
slab_alloc mm/slub.c:2714 [inline]
__kmalloc+0x6e/0x350 mm/slub.c:3747
kmalloc include/linux/slab.h:518 [inline]
tty_buffer_alloc drivers/tty/tty_buffer.c:170 [inline]
__tty_buffer_request_room+0x1cf/0x5e0 drivers/tty/tty_buffer.c:268
tty_insert_flip_string_fixed_flag+0x8f/0x220 drivers/tty/tty_buffer.c:313
tty_insert_flip_string include/linux/tty_flip.h:37 [inline]
pty_write+0x104/0x1d0 drivers/tty/pty.c:121
n_tty_write+0x9a3/0xd90 drivers/tty/n_tty.c:2354
do_tty_write drivers/tty/tty_io.c:958 [inline]
tty_write+0x451/0x8a0 drivers/tty/tty_io.c:1042
__vfs_write+0xef/0x6a0 fs/read_write.c:485
vfs_write+0x184/0x4c0 fs/read_write.c:549
ksys_write+0xc6/0x1a0 fs/read_write.c:598
do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
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 ***
> -ss
>
>