On 09.04.2018 15:07, David Hildenbrand wrote:
> 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);
>
So if everything goes well, we have a replacement for s390x and this
patch should no longer be needed.
pause_all_vcpus/resume_all_vcpus should not be called from a VCPU.
.. that implies that I have to find another way to get all CPUs out KVM
for the prototype I am working on :/
--
Thanks,
David / dhildenb
