From: Longpeng <longpeng2@huawei.com>
We found an issue when repeat reboot in guest during migration, it cause the
migration thread never be waken up again.
<main loop> |<migration_thread>
|
LOCK BQL |
... |
main_loop_should_exit |
pause_all_vcpus |
1. set all cpus ->stop=true |
and then kick |
2. return if all cpus is paused |
(by '->stopped == true'), else|
3. qemu_cond_wait [BQL UNLOCK] |
|LOCK BQL
|...
|do_vm_stop
| pause_all_vcpus
| (A)set all cpus ->stop=true
| and then kick
| (B)return if all cpus is paused
| (by '->stopped == true'), else
| (C)qemu_cond_wait [BQL UNLOCK]
4. be waken up and LOCK BQL | (D)be waken up BUT wait for BQL
5. goto 2. |
(BQL is still LOCKed) |
resume_all_vcpus |
1. set all cpus ->stop=false |
and ->stopped=false |
... |
BQL UNLOCK | (E)LOCK BQL
| (F)goto B. [but stopped is false now!]
|Finally, sleep at step 3 forever.
As suggested by Paolo, resume_all_vcpus should notice this race, so we need
to move the change of runstate before pause_all_vcpus in do_vm_stop() and
ignore the resume request if runstate is not running.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Dr . David Alan Gilbert <dgilbert@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Longpeng <longpeng2@huawei.com>
---
cpus.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/cpus.c b/cpus.c
index b4f8b84..ef441bd 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1026,9 +1026,9 @@ static int do_vm_stop(RunState state, bool send_stop)
int ret = 0;
if (runstate_is_running()) {
+ runstate_set(state);
cpu_disable_ticks();
pause_all_vcpus();
- runstate_set(state);
vm_state_notify(0, state);
if (send_stop) {
qapi_event_send_stop();
@@ -1899,6 +1899,10 @@ void resume_all_vcpus(void)
{
CPUState *cpu;
+ if (!runstate_is_running()) {
+ return;
+ }
+
qemu_clock_enable(QEMU_CLOCK_VIRTUAL, true);
CPU_FOREACH(cpu) {
cpu_resume(cpu);
--
1.8.3.1
On 16/03/20 09:37, Longpeng(Mike) wrote: > From: Longpeng <longpeng2@huawei.com> > > We found an issue when repeat reboot in guest during migration, it cause the > migration thread never be waken up again. > > <main loop> |<migration_thread> > | > LOCK BQL | > ... | > main_loop_should_exit | > pause_all_vcpus | > 1. set all cpus ->stop=true | > and then kick | > 2. return if all cpus is paused | > (by '->stopped == true'), else| > 3. qemu_cond_wait [BQL UNLOCK] | > |LOCK BQL > |... > |do_vm_stop > | pause_all_vcpus > | (A)set all cpus ->stop=true > | and then kick > | (B)return if all cpus is paused > | (by '->stopped == true'), else > | (C)qemu_cond_wait [BQL UNLOCK] > 4. be waken up and LOCK BQL | (D)be waken up BUT wait for BQL > 5. goto 2. | > (BQL is still LOCKed) | > resume_all_vcpus | > 1. set all cpus ->stop=false | > and ->stopped=false | > ... | > BQL UNLOCK | (E)LOCK BQL > | (F)goto B. [but stopped is false now!] > |Finally, sleep at step 3 forever. > > As suggested by Paolo, resume_all_vcpus should notice this race, so we need > to move the change of runstate before pause_all_vcpus in do_vm_stop() and > ignore the resume request if runstate is not running. > > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Dr . David Alan Gilbert <dgilbert@redhat.com> > Cc: Richard Henderson <rth@twiddle.net> > Signed-off-by: Longpeng <longpeng2@huawei.com> Queued, thanks! Paolo > --- > cpus.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/cpus.c b/cpus.c > index b4f8b84..ef441bd 100644 > --- a/cpus.c > +++ b/cpus.c > @@ -1026,9 +1026,9 @@ static int do_vm_stop(RunState state, bool send_stop) > int ret = 0; > > if (runstate_is_running()) { > + runstate_set(state); > cpu_disable_ticks(); > pause_all_vcpus(); > - runstate_set(state); > vm_state_notify(0, state); > if (send_stop) { > qapi_event_send_stop(); > @@ -1899,6 +1899,10 @@ void resume_all_vcpus(void) > { > CPUState *cpu; > > + if (!runstate_is_running()) { > + return; > + } > + > qemu_clock_enable(QEMU_CLOCK_VIRTUAL, true); > CPU_FOREACH(cpu) { > cpu_resume(cpu); >
© 2016 - 2024 Red Hat, Inc.