linux-kernel - Re: tty_ldisc_hangup: waiting (init) for ttyS0 took too long, but we keep waiting...

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Message-ID: <50A2AAA3.7080303@gmail.com>
Date:	Tue, 13 Nov 2012 15:16:35 -0500
From:	Sasha Levin <levinsasha928@...il.com>
To:	Jiri Slaby <jslaby@...e.cz>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: tty_ldisc_hangup: waiting (init) for ttyS0 took too long, but
 we keep waiting...

On 11/13/2012 03:00 PM, Jiri Slaby wrote:
> On 11/10/2012 05:46 AM, Sasha Levin wrote:
>> Hi all,
>>
>> I'm seeing lots of cases when my fuzzing session hangs with a message that
>> starts with:
>>
>> [  104.670841] tty_ldisc_hangup: waiting (init) for ttyS0 took too long, but we keep waiting...
>>
>> And continues with a hung task spew, such as:
>>
>> [  242.990329] INFO: task init:1 blocked for more than 120 seconds.
>> [  242.990955] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> [  242.991527] init            D ffff8800132c0000  3408     1      0 0x00000002
>> [  242.992156]  ffff88001327dc18 0000000000000002 ffff88001327dbd8 ffffffff81152f95
>> [  242.992784]  ffff880013280000 ffff88001327dfd8 ffff88001327dfd8 ffff88001327dfd8
>> [  242.994200]  ffff8800132c0000 ffff880013280000 ffff880013280910 7fffffffffffffff
>> [  242.995780] Call Trace:
>> [  242.996429]  [<ffffffff81152f95>] ? sched_clock_local+0x25/0xa0
>> [  242.997704]  [<ffffffff83bdf065>] schedule+0x55/0x60
>> [  242.999864]  [<ffffffff83bdcea5>] schedule_timeout+0x45/0x360
>> [  243.008415]  [<ffffffff83be077d>] ? _raw_spin_unlock_irqrestore+0x5d/0xb0
>> [  243.008980]  [<ffffffff8117ff8d>] ? trace_hardirqs_on+0xd/0x10
>> [  243.009756]  [<ffffffff83be07a4>] ? _raw_spin_unlock_irqrestore+0x84/0xb0
>> [  243.010662]  [<ffffffff81139e17>] ? prepare_to_wait+0x77/0x90
>> [  243.011452]  [<ffffffff81bb7a56>] tty_ldisc_wait_idle.isra.6+0x76/0xb0
>> [  243.012314]  [<ffffffff81139ff0>] ? abort_exclusive_wait+0xb0/0xb0
>> [  243.013157]  [<ffffffff81bb83bb>] tty_ldisc_hangup+0x1cb/0x320
>> [  243.013927]  [<ffffffff81baf712>] ? __tty_hangup+0x122/0x430
>> [  243.014687]  [<ffffffff81baf71a>] __tty_hangup+0x12a/0x430
>> [  243.015410]  [<ffffffff83be07a4>] ? _raw_spin_unlock_irqrestore+0x84/0xb0
>> [  243.016321]  [<ffffffff81bb187a>] disassociate_ctty+0x6a/0x230
>> [  243.017112]  [<ffffffff811107fa>] do_exit+0x4ea/0xbd0
>> [  243.017793]  [<ffffffff811ccc65>] ? rcu_user_exit+0xc5/0xf0
>> [  243.018549]  [<ffffffff8117ff8d>] ? trace_hardirqs_on+0xd/0x10
>> [  243.019339]  [<ffffffff81110fa4>] do_group_exit+0x84/0xd0
>> [  243.020109]  [<ffffffff81111002>] sys_exit_group+0x12/0x20
>> [  243.020815]  [<ffffffff83be2298>] tracesys+0xe1/0xe6
>> [  243.021607] 1 lock held by init/1:
>> [  243.022079]  #0:  (&tty->ldisc_mutex){+.+...}, at: [<ffffffff81bb8312>] tty_ldisc_hangup+0x122/0x320
>>
>> All of this on latest -next, inside a KVM tools guest.
>>
>> Help appreciated.
> 
> Hi, for me this looks like a false positive. The TTY layer just waits
> for the process sitting on the TTY to vanish. Maybe we should touch the
> watchdogs?

Doesn't it happen only when the process is terminating though? Why would
it take more than 2 minutes to die?


Thanks,
Sasha

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