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SubjectRe: open() on /dev/tty takes 30 seconds on 2.6.36
[I'm not sure whether this is the same issue, but in case it helps... -JimC]

I was about to prepare a bug report about a similar issue which as hit
my (normally headless) compute node. It happened once before I first
booted 2.6.36, and once running 2.6.36. The last two kernels which
I compiled before v2.6.36 were 9c03f16 and bfa88ea; I cannot remember
whether I ever booted 9c03f16. I may have compiled v2.6.36 before
trying 9c03f16. The box is a Phenom, 64bit kernel and userland.

All of the ptys stopped working, which seems like it might be related to
a change in tty locking.

Everything else worked normally; only pty i/o stopped. I couldn't log
in, or use any of my open terminals, but pipes, networking, disk i/o,
et al were all OK.

I was able to use 'ssh server dmesg' to get the dmesg; it had this to say:

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:

INFO: task gpg:15408 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
gpg D ffff8802507ec380 0 15408 15390 0x00000000
ffff8802cf24fd88 0000000000000082 ffff880200000001 0000000000014b00
0000000000014b00 ffff88010a45ae20 ffff8802cf24ffd8 0000000000014b00
0000000000014b00 0000000000014b00 0000000000014b00 ffff8802cf24ffd8
Call Trace:
[<ffffffff815ae2fc>] schedule_timeout+0x36/0xe3
[<ffffffff81047b2b>] ? get_parent_ip+0x11/0x41
[<ffffffff81047b2b>] ? get_parent_ip+0x11/0x41
[<ffffffff815b2b6d>] ? sub_preempt_count+0x97/0xaa
[<ffffffff815ad8a5>] wait_for_common+0xab/0x105
[<ffffffff8104c1c4>] ? default_wake_function+0x0/0x14
[<ffffffff81047b2b>] ? get_parent_ip+0x11/0x41
[<ffffffff81065dd1>] ? __need_more_worker+0x15/0x2c
[<ffffffff810d39ba>] ? lru_add_drain_per_cpu+0x0/0x10
[<ffffffff815ad9b7>] wait_for_completion+0x1d/0x1f
[<ffffffff81066d0d>] flush_work+0x110/0x12e
[<ffffffff81066777>] ? wq_barrier_func+0x0/0x14
[<ffffffff81068831>] schedule_on_each_cpu+0xa8/0xd7
[<ffffffff810d3472>] lru_add_drain_all+0x15/0x17
[<ffffffff810e7786>] sys_mlock+0x30/0xdf
[<ffffffff81009cc2>] system_call_fastpath+0x16/0x1b

(I didn't save the dmesg the first time it happened; I wanted to try .36
before filing a bug report, in case it had already been fixed.)

James Cloos <> OpenPGP: 1024D/ED7DAEA6

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