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A TCG vCPU doing a busy loop systematicaly hangs the QEMU monitor
if the user passes 'device_add' without argument. This is because
drain_cpu_all() which is called from qmp_device_add() cannot return
if readers don't exit read-side critical sections. That is typically
what busy-looping TCG vCPUs do:
int cpu_exec(CPUState *cpu)
{
[...]
rcu_read_lock();
[...]
while (!cpu_handle_exception(cpu, &ret)) {
// Busy loop keeps vCPU here
}
[...]
rcu_read_unlock();
return ret;
}
For MTTCG, have all vCPU threads register a force_rcu notifier that will
kick them out of the loop using async_run_on_cpu(). The notifier is called
with the rcu_registry_lock mutex held, using async_run_on_cpu() ensures
there are no deadlocks.
For RR, a single thread runs all vCPUs. Just register a single notifier
that kicks the current vCPU to the next one.
For MTTCG:
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
For RR:
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Fixes:
|
||
|---|---|---|
| .. | ||
| hvf | ||
| kvm | ||
| qtest | ||
| stubs | ||
| tcg | ||
| xen | ||
| accel-common.c | ||
| accel-softmmu.c | ||
| accel-softmmu.h | ||
| accel-user.c | ||
| dummy-cpus.c | ||
| Kconfig | ||
| meson.build | ||