During we waited on qemu_pause_cond the bql was unlocked,
the vcpu's state may has been changed by other thread, so
we must request the pause state on all vcpus again.
For example:
Both main loop thread and vCPU thread are allowed to call
pause_all_vcpus(), and in general resume_all_vcpus() is called
after it.
Thus there is possibility that during thread T1 waits on
qemu_pause_cond, other thread has called pause_all_vcpus() and
resume_all_vcpus(), then thread T1 will stuck, because the condition
all_vcpus_paused() is always false.
PS:
I hit this bug when I test the RFC patch of ARM vCPU hotplug feature.
This patch is not verified!!! just for RFC.
Signed-off-by: Keqian Zhu <zhukeqi...@huawei.com>
---
system/cpus.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/system/cpus.c b/system/cpus.c
index 68d161d96b..24ac8085cd 100644
--- a/system/cpus.c
+++ b/system/cpus.c
@@ -571,12 +571,14 @@ static bool all_vcpus_paused(void)
return true;
}
-void pause_all_vcpus(void)
+static void request_pause_all_vcpus(void)
{
CPUState *cpu;
- qemu_clock_enable(QEMU_CLOCK_VIRTUAL, false);
CPU_FOREACH(cpu) {
+ if (cpu->stopped) {
+ continue;
+ }
if (qemu_cpu_is_self(cpu)) {
qemu_cpu_stop(cpu, true);
} else {
@@ -584,6 +586,14 @@ void pause_all_vcpus(void)
qemu_cpu_kick(cpu);
}
}
+}
+
+void pause_all_vcpus(void)
+{
+ CPUState *cpu;
+
+ qemu_clock_enable(QEMU_CLOCK_VIRTUAL, false);
+ request_pause_all_vcpus();
/* We need to drop the replay_lock so any vCPU threads woken up
* can finish their replay tasks
@@ -592,9 +602,11 @@ void pause_all_vcpus(void)
while (!all_vcpus_paused()) {
qemu_cond_wait(&qemu_pause_cond, &bql);
- CPU_FOREACH(cpu) {
- qemu_cpu_kick(cpu);
- }
+ /* During we waited on qemu_pause_cond the bql was unlocked,
+ * the vcpu's state may has been changed by other thread, so
+ * we must request the pause state on all vcpus again.
+ */
+ request_pause_all_vcpus();
}
bql_unlock();
--
2.36.1
