Re: [PATCH] monitor: Fix order in monitor_cleanup()

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/10/20 14:50, Kevin Wolf wrote:
> We can only destroy Monitor objects after we're sure that they are not
> in use by the dispatcher coroutine any more. This fixes crashes like the
> following where we tried to destroy a monitor mutex while the dispatcher
> coroutine still holds it:
> 
>   (gdb) bt
>   #0  0x00007fe541cf4bc5 in raise () at /lib64/libc.so.6
>   #1  0x00007fe541cdd8a4 in abort () at /lib64/libc.so.6
>   #2  0x000055c24e965327 in error_exit (err=16, msg=0x55c24eead3a0 <__func__.33> "qemu_mutex_destroy") at ../util/qemu-thread-posix.c:37
>   #3  0x000055c24e9654c3 in qemu_mutex_destroy (mutex=0x55c25133e0f0) at ../util/qemu-thread-posix.c:70
>   #4  0x000055c24e7cfaf1 in monitor_data_destroy_qmp (mon=0x55c25133dfd0) at ../monitor/qmp.c:439
>   #5  0x000055c24e7d23bc in monitor_data_destroy (mon=0x55c25133dfd0) at ../monitor/monitor.c:615
>   #6  0x000055c24e7d253a in monitor_cleanup () at ../monitor/monitor.c:644
>   #7  0x000055c24e6cb002 in qemu_cleanup () at ../softmmu/vl.c:4549
>   #8  0x000055c24e0d259b in main (argc=24, argv=0x7ffff66b0d58, envp=0x7ffff66b0e20) at ../softmmu/main.c:51
> 
> Reported-by: Alex Bennée<alex.bennee@linaro.org>
> Signed-off-by: Kevin Wolf<kwolf@redhat.com>

Is this a race, or is there a chance of adding a reliable reproducer to 
qtest?

Paolo