linux-kernel - Re: open() on /dev/tty takes 30 seconds on 2.6.36

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Date:	Sun, 31 Oct 2010 12:36:38 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	James Cloos <cloos@...loos.com>
Cc:	Eli Billauer <eli@...lauer.co.il>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>
Subject: Re: open() on /dev/tty takes 30 seconds on 2.6.36

On Sunday 31 October 2010, James Cloos wrote:
> WARNING: at kernel/workqueue.c:1180 worker_enter_idle+0xd6/0xe2()
> Hardware name: MS-7642
> Modules linked in: tcp_diag inet_diag ipt_addrtype xt_dscp xt_string xt_owner xt_multiport xt_iprange xt_hashlimit xt_DSCP xt_NFQUEUE xt_mark xt_connmark tun snd_pcm_oss snd_mixer_oss snd_usb_audio snd_usbmidi_lib snd_rawmidi tpm_tis tpm ppdev parport_pc tpm_bios parport serio_raw edac_core k10temp pcspkr i2c_piix4 shpchp
> Pid: 8061, comm: kworker/0:1 Not tainted 2.6.36-carbon1 #18
> Call Trace:
>  [<ffffffff81050c60>] warn_slowpath_common+0x85/0x9d
>  [<ffffffff81050c92>] warn_slowpath_null+0x1a/0x1c
>  [<ffffffff81066861>] worker_enter_idle+0xd6/0xe2
>  [<ffffffff81068453>] worker_thread+0x182/0x19b
>  [<ffffffff810682d1>] ? worker_thread+0x0/0x19b
>  [<ffffffff8106ba81>] kthread+0x82/0x8a
>  [<ffffffff8100aae4>] kernel_thread_helper+0x4/0x10
>  [<ffffffff8106b9ff>] ? kthread+0x0/0x8a
>  [<ffffffff8100aae0>] ? kernel_thread_helper+0x0/0x10
> ---[ end trace 756b0818a6415dca ]---
> 
> That was followed by a number of task blocked for more than 120 seconds
> messages, all due to waiting for pty input or output.  An example trace:

This is triggered by an internal check in the workqueue handling that
Tejun introduced. I guess it might be possible that this is triggered by
a worker thread being blocked on a mutex, but I don't understand
exactly what it is checking for. 

	Arnd

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