From: Longpeng <[email protected]>
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.
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: Dr. David Alan Gilbert <[email protected]>
Cc: Richard Henderson <[email protected]>
Signed-off-by: Longpeng <[email protected]>
Suggested-by: Paolo Bonzini <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
---
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
