Re: [Qemu-devel] [PATCH v11 0/7] trace: Generic event state description

[Lluís Vilanova]

Stefan Hajnoczi writes:

> On Fri, Mar 01, 2013 at 04:29:35PM +0100, Lluís Vilanova wrote:
>> Provides a generic event state description structure (TraceEvent) and a more
>> detailed event control and query interface.
>> 
>> This is achieved by creating a new "non-public" tracing backend (i.e., not
>> selectable by the user at configure time) that will generate the appropriate
>> event description information.
>> 
>> Signed-off-by: Lluís Vilanova <address@hidden>
>> ---
>> 
>> Changes in v11:
>> 
>> * Rebase on a4bcea3 from master.

> Hi Lluís,
> Thanks for rebasing.  Unfortunately I still hit the hang on shutdown
> with the simple trace backend.

> Steps to reproduce:
> $ ./configure --target-list=x86_64-softmmu --enable-trace-backend=simple
> $ make
> $ cat my-events
> bdrv_open_common
> $ x86_64-softmmu/qemu-system-x86_64 \
>       -enable-kvm -m 1024 \
>       -trace events=my-events \
>       -drive if=virtio,cache=none,file=test.img
> Ctrl-Alt-2
> (qemu) quit
> ...hang...

> Please let me know if you are able to reproduce it.  qemu.git/master
> does not behave this way.

I've been unable to reproduce it with v11, but was able to using v10 (although
only a couple of times).

What I saw in v10 looked like a deadlock between 'flush_trace_file' and
'wait_for_trace_records_available' (both use 'trace_lock'), but I only was able
to reproduce it a couple of times, so I couldn't haunt the problem down.

After a quick re-read of the patches, the changes should have no effect on how
the mutexes in the "simple" backend are handled, so maybe the problem is not
related to this change (it just makes it more frequent in your build).

Could it be possible that you exit QEMU before calling 'trace_backend_init'?
(as unlikely as it might be)



Lluis

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