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

[Programmingkid]

On May 10, 2015, at 10:54 AM, Paolo Bonzini wrote:

> 
> 
> 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

OK, I see a pattern. SDL and CoreAudio both don't support audio input. Both of 
them have this code:
 .voice_size_in  = 0

Alsa and PulseAudio do support audio input and work. Coincidence?