linux-kernel - Re: Deadlock?: console_waiter/serial8250_ports/low_water

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Message-ID: <CANDhNCpaJ85EvMvjs+Qpgnohpo_cy96PGXJ7Y3S6SOZ2iaG9aA@mail.gmail.com>
Date: Mon, 28 Oct 2024 12:54:35 -0700
From: John Stultz <jstultz@...gle.com>
To: John Ogness <john.ogness@...utronix.de>, Petr Mladek <pmladek@...e.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, jirislaby@...nel.org, 
	Boqun Feng <boqun.feng@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>, kernel-team@...roid.com
Subject: Re: Deadlock?: console_waiter/serial8250_ports/low_water_lock with 6.12-rc

On Mon, Oct 28, 2024 at 12:30 PM John Stultz <jstultz@...gle.com> wrote:
> * One thread is in virt_spin_lock (lock=lock@...ry=0xffffffff843d19a0
> <serial8250_ports>) at ./arch/x86/include/asm/qspinlock.h:106.  The
> backtrace there, is similarly going through
> do_exit()->check_stack_usage()->printk (I suspect blocking all the
> other cpus), where it hits: serial8250_console_write
> (up=0xffffffff843d19a0 <serial8250_ports>, s=0xffffffff8434f7e0
> <printk_shared_pbufs> "[   69.857641] \n", count=<optimized out>) at
> drivers/tty/serial/8250/8250_port.c:3352,  then into the spinlock
> code.
>

I got a question on IRC about the backtrace for this cpu, so I wanted
to also share it here as well.

#0  virt_spin_lock (lock=lock@...ry=0xffffffff843d19a0
<serial8250_ports>) at ./arch/x86/include/asm/qspinlock.h:106
#1  queued_spin_lock_slowpath (lock=lock@...ry=0xffffffff843d19a0
<serial8250_ports>, val=1) at kernel/locking/qspinlock.c:324
#2  0xffffffff8112954e in queued_spin_lock (lock=0xffffffff843d19a0
<serial8250_ports>) at ./include/asm-generic/qspinlock.h:114
#3  do_raw_spin_lock (lock=lock@...ry=0xffffffff843d19a0
<serial8250_ports>) at kernel/locking/spinlock_debug.c:116
#4  0xffffffff82177e67 in __raw_spin_lock_irqsave
(lock=0xffffffff843d19a0 <serial8250_ports>) at
./include/linux/spinlock_api_smp.h:111
#5  _raw_spin_lock_irqsave (lock=lock@...ry=0xffffffff843d19a0
<serial8250_ports>) at kernel/locking/spinlock.c:162
#6  0xffffffff817723d0 in uart_port_lock_irqsave (flags=<synthetic
pointer>, up=0xffffffff843d19a0 <serial8250_ports>) at
./include/linux/serial_core.h:711
#7  serial8250_console_write (up=0xffffffff843d19a0
<serial8250_ports>, s=0xffffffff8434f7e0 <printk_shared_pbufs> "[
69.857641] \n", count=<optimized out>)
    at drivers/tty/serial/8250/8250_port.c:3352
#8  0xffffffff8113ef11 in console_emit_next_record (cookie=<optimized
out>, handover=<optimized out>, con=0xffffffff82e11e40
<univ8250_console>)
    at kernel/printk/printk.c:3092
#9  console_flush_all (do_cond_resched=do_cond_resched@...ry=false,
next_seq=next_seq@...ry=0xffffc9000274fdb8,
handover=handover@...ry=0xffffc9000274fdb3)
    at kernel/printk/printk.c:3180
#10 0xffffffff8113f1a3 in __console_flush_and_unlock () at
kernel/printk/printk.c:3239
#11 console_unlock () at kernel/printk/printk.c:3279
#12 0xffffffff8113f745 in vprintk_emit (facility=0, level=<optimized
out>, dev_info=0x0 <fixed_percpu_data>,
    fmt=0xffffffff8297cc28 "\0016%s (%d) used greatest stack depth:
%lu bytes left\n", args=0xffffc9000274fe30) at
kernel/printk/printk.c:2407
#13 0xffffffff8113b9d4 in _printk (fmt=fmt@...ry=0xffffffff8297cc28
"\0016%s (%d) used greatest stack depth: %lu bytes left\n") at
kernel/printk/printk.c:2432
#14 0xffffffff810994d0 in check_stack_usage () at ./include/linux/pid.h:232
#15 do_exit (code=code@...ry=0) at kernel/exit.c:982
#16 0xffffffff81099876 in do_group_exit (exit_code=0) at kernel/exit.c:1088
#17 0xffffffff81099908 in __do_sys_exit_group (error_code=<optimized
out>) at kernel/exit.c:1099
#18 __se_sys_exit_group (error_code=<optimized out>) at kernel/exit.c:1097
#19 __x64_sys_exit_group (regs=<optimized out>) at kernel/exit.c:1097
#20 0xffffffff81003ab3 in x64_sys_call (regs=<optimized out>,
nr=<optimized out>) at
./arch/x86/include/generated/asm/syscalls_64.h:232
#21 0xffffffff8216267b in do_syscall_x64 (nr=231,
regs=0xffffc9000274ff58) at arch/x86/entry/common.c:52
#22 do_syscall_64 (regs=0xffffc9000274ff58, nr=231) at
arch/x86/entry/common.c:83
#23 0xffffffff82200130 in entry_SYSCALL_64 () at arch/x86/entry/entry_64.S:121
#24 0x0000000000000000 in ?? ()


thanks
-john