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Re: [Qemu-devel] [Block-io] qemu virtual machine get stuck during startu


From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [Block-io] qemu virtual machine get stuck during startup
Date: Thu, 19 Oct 2017 15:29:07 +0200
User-agent: Mutt/1.9.1 (2017-09-22)

On Thu, Oct 19, 2017 at 05:32:10PM +0800, Wahaha Huang wrote:
> Hi there,
> I'm a newbie of qemu(2.10.0), when i start a vm from qemu, it sometimes get
> stuck,

Please post your QEMU command-line and describe the behavior when it
gets stuck.

Are there any error messages?  Does the QEMU monitor still work?  Is the
QEMU process running at 100% CPU?  etc

> through gdb debugging, i found aio_worker thread(list below) missing when
> vm get stuck,
> but i don't know why, does anybody has further idea about this?

Worker threads are temporary threads.  If there is no work to do then
they terminate.  New worker threads are started as needed.  Therefore
you can't assume that a specific number of worker threads exists.

> (gdb) info threads
> >
> >   Id   Target Id         Frame
> >
> >   1    LWP 25451 "qemu-system-x86" 0x00007fc62081dc8b in ppoll () from
> >> /lib/libc.so.6
> >
> >   2    LWP 25452 "qemu-system-x86" 0x00007fc620823ee9 in syscall () from
> >> /lib/libc.so.6
> >
> > * 3    LWP 25495 "qemu-system-x86" 0x00007fc620af8e80 in ?? () from
> >> /lib/libpthread.so.0
> >
> >   4    LWP 25496 "qemu-system-x86" 0x00007fc62081f697 in ioctl () from
> >> /lib/libc.so.6
> >
> >   5    LWP 25497 "qemu-system-x86" 0x00007fc62081f697 in ioctl () from
> >> /lib/libc.so.6
> >
> >   6    LWP 25498 "qemu-system-x86" 0x00007fc62081db9d in poll () from
> >> /lib/libc.so.6
> >
> >   7    LWP 25500 "threaded-ml" 0x00007fc62081db9d in poll () from
> >> /lib/libc.so.6

This looks like PulseAudio.  I suggest disabling audio and checking if
the hang still occurs.

> >
> >   8    LWP 25501 "qemu-system-x86" 0x00007fc620af5e1d in pthread_cond_wait
> >> () from /lib/libpthread.so.0
> >
> >   9    LWP 25502 "qemu-system-x86" 0x00007fc620af5e1d in pthread_cond_wait
> >> () from /lib/libpthread.so.0
> >
> > (gdb) bt
> >
> > #0  0x00007fc620af8e80 in  () at /lib/libpthread.so.0
> >
> > #1  0x00007fc620af8f5f in  () at /lib/libpthread.so.0
> >
> > #2  0x00007fc620af906f in sem_timedwait () at /lib/libpthread.so.0
> >
> > #3  0x000055b66332e585 in qemu_sem_timedwait (sem=0x55b664e6c868,
> >> ms=10000) at util/qemu-thread-posix.c:289
> >
> > #4  0x000055b6633279b6 in worker_thread (opaque=0x55b664e6c7f0) at
> >> util/thread-pool.c:102
> >
> > #5  0x00007fc620aef767 in  () at /lib/libpthread.so.0
> >
> > #6  0x00007fc62082985f in clone () at /lib/libc.so.6

This is a worker thread waiting for more work to do.  It's normal.



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