linux-kernel - Re: (WARNING) possible deadlock in del_timer_sync, called from fbcon_del_cursor

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Date:	Thu, 3 Mar 2011 17:12:12 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Clemens Ladisch <clemens@...isch.de>, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Jason Wessel <jason.wessel@...driver.com>
Subject: Re: (WARNING) possible deadlock in del_timer_sync, called from fbcon_del_cursor_timer

On Thu, Mar 3, 2011 at 2:12 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Mon, Feb 28, 2011 at 03:41:07PM +0100, Clemens Ladisch wrote:
>> While using the FB console, I tried to change the console log level
>> with SysRq, and got this warning that del_timer_sync() is used in
>> an interrupt handler:
>
> Ug, del_timer_sync() can be called from interrupt context:
>
> printk -> vt_console_print -> hide_cursor -> fbcon_cursor
> -> fbcon_del_cursor_time -> del_timer_sync()
>
> printk is allowed to be called from interrupt context. This is indeed a
> true bug.

Yeah.

And more explanation for that WARN_ON() :)

run_timer_softirq(SOFTIRQ context)
  cursor_timer_handler()
  Interrupt comes in(IRQ context)
    ...
      del_timer_sync()
        deadlock

So fbcon guys:
Could above situation happen?

Cc'ing people from:
./scripts/get_maintainer.pl -f drivers/video/console/fbcon.c

Thanks,
Yong


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