linux-kernel - Re: [lkp] [panic] [ BUG: bad unlock balance detected! ]

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Date:	Mon, 16 Nov 2015 16:43:00 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	kernel test robot <ying.huang@...ux.intel.com>
Cc:	Vitaly Kuznetsov <vkuznets@...hat.com>, lkp@...org,
	LKML <linux-kernel@...r.kernel.org>, Jan Kara <jack@...e.cz>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Seth Jennings <sjenning@...hat.com>,
	Xie XiuQi <xiexiuqi@...wei.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Baoquan He <bhe@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [lkp] [panic] [ BUG: bad unlock balance detected! ]

On Mon, 16 Nov 2015 11:12:50 +0800 kernel test robot <ying.huang@...ux.intel.com> wrote:

> FYI, we noticed the below changes on
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> commit 08d78658f393fefaa2e6507ea052c6f8ef4002a2 ("panic: release stale console lock to always get the logbuf printed out")
> 
> ...
>
> [   38.408623] =====================================
> [   38.408623] [ BUG: bad unlock balance detected! ]
> [   38.408627] 4.3.0-08150-g08d7865 #1 Not tainted
> [   38.408627] -------------------------------------
> [   38.408631] swapper/0/1 is trying to release lock (console_lock) at:
> [   38.408639] [<ffffffff811a3cb1>] panic+0x124/0x213
> [   38.408640] but there are no more locks to release!
> [   38.408641] 
> [   38.408641] other info that might help us debug this:
> [   38.408642] 2 locks held by swapper/0/1:
> [   38.408651]  #0:  (oom_lock){+.+...}, at: [<ffffffff811add45>] __alloc_pages_slowpath+0x5bd/0x68d
> [   38.408656]  #1:  (panic_lock){......}, at: [<ffffffff811a3bd9>] panic+0x4c/0x213
> [   38.408657] 
> [   38.408657] stack backtrace:
> [   38.408659] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.3.0-08150-g08d7865 #1
> [   38.408660] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
> [   38.408665]  0000000000000000 ffff8800132bba78 ffffffff8173760d ffff8800132b4040
> [   38.408668]  ffff8800132bbaa0 ffffffff8111328c 00000000ffffffff ffff8800132b4040
> [   38.408670]  ffffffff8406a080 ffff8800132bbb18 ffffffff8111626c ffffffff811139d1
> [   38.408671] Call Trace:
> [   38.408678]  [<ffffffff8173760d>] dump_stack+0x4b/0x63
> [   38.408682]  [<ffffffff8111328c>] print_unlock_imbalance_bug+0xc7/0xd0

Yup, we can't have this happen.

Can we instead do this?

	if (is_console_locked())
		console_unlock();

It's racy, but more accurate than what we have now?
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