[Xen-bugs] [Bug 415] New: daemon polling turns into endless loop

[bugzilla-daemon@xxxxxxxxxxxxxxxxxxx]

http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=415

           Summary: daemon polling turns into endless loop
           Product: Xen
           Version: 2.0
          Platform: x86
        OS/Version: Linux
            Status: NEW
          Severity: critical
          Priority: P2
         Component: Hypervisor
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: john.wells@xxxxxxxxxx


We're having a similar problem to that documented, but not resolved, here:
http://lists.xensource.com/archives/html/xen-users/2005-08/msg00110.html

The python process that runs "/usr/sbin/xend start" has reached 99.9% CPU
utilization.

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 3569 root      25   0 12952 7876 2456 R 99.9  6.2  13444:26 python
/usr/sbin/xend start

xm commands don't respond, because the daemon process has apparently
entered an endless loop. 

If you strace a normally running xend process, you'll see:

gettimeofday({1132084397, 346225}, NULL) = 0xen.xend.server import SrvDaemon
gettimeofday({1132084397, 346536}, NULL) = 0= SrvDaemon.instance()
poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=6, events=POLLIN},
{fd=10, events=POLLIN}, {fd=15, events=POLLIN}, {fd=18, events=POLLIN}],
6, 178) = 0
gettimeofday({1132084397, 534960}, NULL) = 0
gettimeofday({1132084397, 535283}, NULL) = 0

That poll line is key...the daemon is apparently polling for commands issued
from the user.

When the bug occurs, this polling stops. The daemon is thrown into an endless
loop where gettimeofday is called rapidly in succession. Stracing to the process
yields:

gettimeofday({1132076987, 801316}, NULL) = 0
gettimeofday({1132076987, 801401}, NULL) = 0
gettimeofday({1132076987, 801486}, NULL) = 0
gettimeofday({1132076987, 801571}, NULL) = 0
gettimeofday({1132076987, 801657}, NULL) = 0
gettimeofday({1132076987, 801742}, NULL) = 0
gettimeofday({1132076987, 801828}, NULL) = 0
gettimeofday({1132076987, 801913}, NULL) = 0
gettimeofday({1132076987, 801999}, NULL) = 0
gettimeofday({1132076987, 802084}, NULL) = 0
...over, and over, and over again.

This is on a CentOS4 (RHEL4) box, on an i686.
Kernel: 2.6.11.12-xen0
Xen version: 2.0.7

The only resolution we've found is rebooting the host box.

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