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

From: arnd
Date: Wed Jun 09 2010 - 17:16:44 EST

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
> 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://

> 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?

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