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

[Kevin Wolf]

Am 15.02.2021 um 16:08 hat Paolo Bonzini geschrieben:
> 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?

It is a race, but it's a fix for a bug that was caught by one of the
acceptance tests quite reliably. Alex reported it here:

https://lists.gnu.org/archive/html/qemu-devel/2020-10/msg03124.html

So I think to the extent that we can have a reliable test case, we
probably have one, even if it wasn't written specifically for this bug.
But it's not run during 'make check' if this is what you had in mind.

Kevin