[Xen-devel] Known console(d) bug?

[Ferenc Wagner <wferi@xxxxxxx>]

Hi,

There's a problem I'm struggling with for quite some time in our Xen
hosting environment.  Basically, after a couple of months' smooth
running time, suddenly most virtual machines get stuck into r state
and stop responding to anything, including xm console and xm sysrq.
It happens rather regularly, but I can't reproduce it by taxing the
domUs or the dom0 with disk I/O, CPU or console I/O.

However, a couple of days ago it turned out that this situation can be
cured by restarting xenconsoled!  After that, xm console spit out the
previous random typing, sysrq help strings and whatnot for the domUs
which weren't stuck in r state, and the stuck ones also started to
respond and run normally (spending most of their time in b state) again.

The whole phenomenon looked like xenconsoled stopped emptying the domU
console buffers, and those domUs which were constantly writing to
their consoles quickly filled it up and started busy-looping trying to
put more characters onto their consoles, not caring to respond to
ping, even.  But those domUs which didn't write to their consoles,
stayed functional until the desperate operator forced them to create
enough console output to fill up their buffers as well, and then they
stuck into r state just like the others.  After restarting xenconsoled
all were able to recover successfully.

Of course the above is just guessing, I don't know the details of Xen
console handling.  But I wonder if it rings any bells here, or maybe
this issue is known and fixed already.  Oh, I experience this under
Xen 3.2 and pv-ops guests (2.6.26+patches).
-- 
Thanks,
Feri.

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