[Xen-bugs] [Bug 30] New: fast output on console blocks DomU and crashed XEND taking 100% of the host

[bugzilla-daemon@xxxxxxxxxxxxxxxxxxx]

http://bugzilla.xensource.com/cgi-bin/bugzilla/show_bug.cgi?id=30

           Summary: fast output on console blocks DomU and crashed XEND
                    taking 100% of the host
           Product: Xen
           Version: 2.0
          Platform: x86
        OS/Version: Linux-2.6
            Status: NEW
          Severity: critical
          Priority: P1
         Component: Unspecified
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: xenbugs@xxxxxxxxxxx


If a DomU has lots of fast output on the console it hangs (blocks). If this
happens the xend on the host crashes and starts taking up 100% cpu usage. 

If you kill xend on the host and restart it you can reconnect to the console on
the DomU and it may run for an additional few seconds, than it crashes again
after the same large amount of output has been send to the console. 

This can be reproduced with the xen-live-cd by starting a DomU, connect to its
console and issueing a 'cat /dev/urandom|strings' (it's not a binairy problem!)

However this is NOT something that in real live never happens!
a reiserfsck for example sends out lots of information on the console making it
impossible to restart a DomU with a damaged reiserFS. To make things worse the
console of the system doesn't even have to be attached to the host, just
issueing a 'xm create ./xenconf' will cause xend to crash on our box!.

Our impression is that many of the problems we have with xen are related to this
problem. For instance when a xen crashes it sometimes causes the xend-db to be
corrupt. Most of the time rebuilding that takes a lot of manual effort and may
not even work at all. Without this database many things are impossible to do
(attaching to consoles, shutting them down etcetc).

This bug is a mayor one for the stable use of XEN. Anyone that makes the mistake
of typing 'cat __INSERT LARGE FILE HERE___' can cause major problems for its own
domain, for the performance of the intire box and for the people mainting it (us
in this case).
Please consider fixing this one asap.



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