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-   -   ssh sessions with pseudo terminal hang when in kernel events thread hangs (http://www.linux-archive.org/debian-user/646347-ssh-sessions-pseudo-terminal-hang-when-kernel-events-thread-hangs.html)

Sven Hoexter 03-19-2012 12:04 PM

ssh sessions with pseudo terminal hang when in kernel events thread hangs
 
Hi,
since about December we see machines where interactive ssh sessions hang or
logins are no longer possible. The machine itself is still alive and
using ssh without pseudo terminal allocation works fine (ssh -T).

What we have so far is that this happens on systems with Linux 2.6.32.
(Mostly Debian but we've seen this on one RHEL 6.1 system aswell but there
the patch level was too far off to open a support case.)

Sometimes ssh logins work for a short time, e.g. you see motd and get no prompt
or you can execute a few commands and suddenly it hangs.

Pseudo terminals are allocated just fine and device nodes can bee seen
in /dev/pts/.

When it happens we can see one of the in kernel [events/$x] processes
to be in state D and the number of context switches and interrupts goes
up by factor 6. Most of those interrupts seem to be generated by
hpet on the CPU where the events/$x process is running ($x = number
of the CPU/CPU core of this system).


Has someone seen a similar behaviour? We currently have no idea
how and why it happens. It's all Dell Hardware we're running on
(R210, 410, 710).

Regards,
Sven


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