Re: [Qemu-devel] Help with deadlock when using sound

[Paolo Bonzini]

On 06/05/2015 18:40, Programmingkid wrote:
> When I try to use the pcspk sound hardware, QEMU freezes and uses
> 100% of the cpu time. This is the command I use:
> 
> qemu-system-i386 -cdrom <anything you wan here> -soundhw pcspk
> 
> This looks like a deadlock situation because some unknown code called
> qemu_mutex_lock(). Here is the stack trace at the freeze:
> 
> (gdb) bt #0  0x00007fff824e2db6 in semaphore_wait_trap () #1
> 0x00007fff824e8417 in pthread_mutex_lock () #2  0x0000000100267199 in
> qemu_mutex_lock (mutex=<value temporarily unavailable, due to
> optimizations>) at util/qemu-thread-posix.c:73 #3  0x003c44016e95153b
> in ?? ()
> 
> My host is Mac OS 10.6.8. My guest isn't really anything. I have used
> Windows XP before but it isn't necessary to reproduce the problem.
> 
> The ?? is what appears to be the problem. I can't even print
> instructions at that address. Any ideas as to what is calling the
> qemu_mutex_lock() function could help.

Reproduced with a FreeDOS image from QEMU Advent Calendar.  It locks up
as soon as you type "beep".

It works with the PulseAudio and ALSA backends, but it doesn't with the
SDL backend, even on Linux.

Also, it deadlocks even with KVM enabled.

Paolo