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To protect data accessed by main_thread (most spice channels) from being accessed by threads of other channels (namely, the display and cursor channels), an assert was coded in spice-server.
Some calls to the sound channel interface can be done from the vcpu thread. Such accesses hit the assert code, and made spice-server (and qemu-kvm) to abort.
Such accesses are safe as qemu-kvm uses global
mutex for the vcpu and io threads.
Those assert lines of code were replaced by a warning.
spice-server does not abort on such accesses.