linux-kernel - Re: Soft lockup during suspend since ~2.6.36

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Date:	Mon, 4 Apr 2011 05:02:52 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Thilo-Alexander Ginkel" <thilo@...kel.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Soft lockup during suspend since ~2.6.36

On Sunday 03 April 2011, Thilo-Alexander Ginkel wrote:
> Transcript:
> | RIP: _raw_spin_unlock_irqrestore
> | Call Stack:
> |   _set_cpus_allowed_ptr
> |   worker_maybe_bind_and_lock
> |   rescuer_thread
> |   rescuer_thread
> |   kernel_thread_helper
> |   kthread
> |   kernel_thread_helper
> |   kthread
> 
> After some more time, the following backtrace is printed:
>   https://secure.tgbyte.de/dropbox/ueph3Ohm-3.jpg
> 
> Transcript:
> | RIP: worker_maybe_bind_and_lock
> | Call Stack:
> |   rescuer_thread
> |   rescuer_thread
> |   kernel_thread_helper
> |   kthread
> |   kernel_thread_helper
> |   kthread
> 
> From then on these two backtraces are printed in an alternating fashion.
> 
> Unfortunately, the top of the output is missing as it does not fit on
> screen (does someone know an even smaller console font?), but I assume
> it's the deadlock detection.

The interesting thing is that the backtrace is from unlock, not from lock,
so it can't really be a deadlock. However, the _raw_spin_unlock_irqrestore
function calls debug_spin_unlock(), which does a few sanity check. Maybe
one of those got triggered.

The easiest way to get the full output is usually to attach a serial
NULL modem cable and redirect the console to that, so you can get the
output on another machine. Another idea would be to modify the
show_registers function in arch/x86/kernel/dumpstack_64.c so that
it prints less data.

Yet another idea would be to set /sys/kernel/printk_delay so that the
oops gets printed slower.

	Arnd
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