If we have parallel calls to resume/pause_all_vcpus() we can get into trouble because the qemu mutex is temporarily dropped while waiting for all threads to stop. This can happen e.g. for s390x, where resume/pause_all_vcpus() can be triggered by a VCPU.
Pause/Resume exactly once, when we leave/hit "0". Signed-off-by: David Hildenbrand <da...@redhat.com> --- cpus.c | 31 ++++++++++++++++++++++++------- 1 file changed, 24 insertions(+), 7 deletions(-) diff --git a/cpus.c b/cpus.c index 2e6701795b..7c7e0245c5 100644 --- a/cpus.c +++ b/cpus.c @@ -1778,17 +1778,26 @@ static bool all_vcpus_paused(void) return true; } +/* wait for the initial vm_start() call */ +static int vcpus_paused = 1; + void pause_all_vcpus(void) { CPUState *cpu; - qemu_clock_enable(QEMU_CLOCK_VIRTUAL, false); - CPU_FOREACH(cpu) { - if (qemu_cpu_is_self(cpu)) { - qemu_cpu_stop(cpu, true); - } else { - cpu->stop = true; - qemu_cpu_kick(cpu); + assert(qemu_mutex_iothread_locked()); + assert(vcpus_paused >= 0); + + vcpus_paused++; + if (vcpus_paused == 1) { + qemu_clock_enable(QEMU_CLOCK_VIRTUAL, false); + CPU_FOREACH(cpu) { + if (qemu_cpu_is_self(cpu)) { + qemu_cpu_stop(cpu, true); + } else { + cpu->stop = true; + qemu_cpu_kick(cpu); + } } } @@ -1820,6 +1829,14 @@ void resume_all_vcpus(void) { CPUState *cpu; + assert(vcpus_paused >= 0); + assert(qemu_mutex_iothread_locked()); + + vcpus_paused--; + if (vcpus_paused > 0) { + return; + } + qemu_clock_enable(QEMU_CLOCK_VIRTUAL, true); CPU_FOREACH(cpu) { cpu_resume(cpu); -- 2.14.3