linux-kernel - Re: PROBLEM: PPP and other serial port related application hangs in kernel space

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Date:	Wed, 9 Jun 2010 23:16:32 +0200
From:	arnd@...db.de
To:	Ales Teska <ales.teska@...il.com>
Cc:	linux-kernel@...r.kernel.org, Greg KH <gregkh@...e.de>,
	Alan Cox <alan@...ux.intel.com>
Subject: Re: PROBLEM: PPP and other serial port related application hangs in kernel space

On Wednesday 09 June 2010 22:46:28 Ales Teska wrote:
> after upgrade of Linux kernel to version 2.6.34 I started to observe following problem 
> - ppp and other serial port related application occasionally (in 1 hour or 1/10 ppp 
> connections) 'hangs' (see description bellow) rendering related serial device unusable.
> I backtracked this issue to 2.6.32.15.
> Application remains in the condition marked as 'D' in 'ps' output (waiting for result
> from kernel space, if I understand that correctly); it stays in this condition forever.

It would be good to find out where exactly the application hangs. Please try a sysrq-t
(press Alt+SysRq+t simultaneously) or cat /proc/<pid-that-hangs>/stack.

It might also be helpful to try running the kernel with CONFIG_LOCKDEP and/or
CONFIG_TTY_MUTEX enabled. For the latter one, you need to get the source
from the tty branch of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl.git

> I also found following information in dmesg:
> [ 1673.660876] ------------[ cut here ]------------
> [ 1673.661471] WARNING: at drivers/char/tty_io.c:1278 tty_open+0x213/0x451()
> [ 1673.662358] Modules linked in: ppp_deflate zlib_deflate bsd_comp ppp_async crc_ccitt ppp_generic slhc ipv6 nvram msr cpuid ledtrig_timer ledtrig_heartbeat ledtrig_default_on geodewdt lm90 hwmon scx200_acb option usbserial ehci_hcd ohci_hcd via_rhine usbcore leds_alix2 mii
> [ 1673.689168] Pid: 1275, comm: ufoprobe_client Not tainted 2.6.34-486-exiprobes #1
> [ 1673.690452] Call Trace:
> [ 1673.690947]  [<c10e93af>] ? tty_open+0x213/0x451
> [ 1673.691926]  [<c1018f51>] warn_slowpath_common+0x45/0x5c
> [ 1673.693006]  [<c1018f75>] warn_slowpath_null+0xd/0x10
> [ 1673.694293]  [<c10e93af>] tty_open+0x213/0x451
> [ 1673.694755]  [<c1068105>] chrdev_open+0xe3/0x126

Do you always see this message exactly once before it hangs?

	Arnd
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