[Qemu-devel] qemu-system-ppc64 hanging occasionally in disk writes

["Richard W.M. Jones" <rjones@redhat.com>]

I found last week that qemu-system-ppc64 (from git) hangs occasionally
under load, and I have a reproducer for it now.  Unfortunately the
reproducer really takes a long time to run -- usually I can get a hang
in under 12 hours.

Here is the reproducer case:

  https://lists.fedoraproject.org/pipermail/ppc/2012-June/001698.html

Notes:

(1) Verified by one other person (other than me).  Happens on both
    ppc64 and x86-64 host.

(2) Happens with both Fedora guest kernel 3.3.4-5.fc17.ppc64 and kernel
    3.5.0 that I compiled myself.  The test case above contains 3.3.4-5.

(3) Seems to be a problem in qemu, not the guest.  The reason I think
    this is because I tried to capture a backtrace of the hang using
    remote gdb, but gdb just hung when trying to connect to qemu
    (gdb connects fine before the bug happens).

(4) Judging by guest messages, appears to be happening when writing
    to the disk.

Reported: https://bugs.launchpad.net/qemu/+bug/1013241

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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