diff options
authorPeter Maydell <peter.maydell@linaro.org>2019-01-07 15:23:47 +0000
committerPeter Maydell <peter.maydell@linaro.org>2019-01-07 15:23:47 +0000
commit0ec7e6779fc830e5b4e6a448d75317fafcf69477 (patch)
parentb7f301141d68be12f074db4ebfc51508f952ea61 (diff)
cpus.c: Fix race condition in cpu_stop_current()
We use cpu_stop_current() to ensure the current CPU has stopped from places like qemu_system_reset_request(). Unfortunately its current implementation has a race. It calls qemu_cpu_stop(), which sets cpu->stopped to true even though the CPU hasn't actually stopped yet. The main thread will look at the flags set by qemu_system_reset_request() and call pause_all_vcpus(). pause_all_vcpus() waits for every cpu to have cpu->stopped true, so it can continue (and we will start the system reset operation) before the vcpu thread has got back to its top level loop. Instead, just set cpu->stop and call cpu_exit(). This will cause the vcpu to exit back to the top level loop, and there (as part of the wait_io_event code) it will call qemu_cpu_stop(). This fixes bugs where the reset request appeared to be ignored or the CPU misbehaved because the reset operation started to change vcpu state while the vcpu thread was still using it. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Emilio G. Cota <cota@braap.org> Tested-by: Jaap Crezee <jaap@jcz.nl> Message-id: 20181207155911.12710-1-peter.maydell@linaro.org
1 files changed, 2 insertions, 1 deletions
diff --git a/cpus.c b/cpus.c
index 0ddeeefc14..b09b702712 100644
--- a/cpus.c
+++ b/cpus.c
@@ -2100,7 +2100,8 @@ void qemu_init_vcpu(CPUState *cpu)
void cpu_stop_current(void)
if (current_cpu) {
- qemu_cpu_stop(current_cpu, true);
+ current_cpu->stop = true;
+ cpu_exit(current_cpu);