diff mbox series

[PULL,22/37] cpus.c: Fix race condition in cpu_stop_current()

Message ID 20190107163117.16269-23-peter.maydell@linaro.org
State Accepted
Commit 0ec7e6779fc830e5b4e6a448d75317fafcf69477
Headers show
Series target-arm queue | expand

Commit Message

Peter Maydell Jan. 7, 2019, 4:31 p.m. UTC 
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
---
 cpus.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

-- 
2.19.2
diff mbox series

Patch

diff --git a/cpus.c b/cpus.c
index 0ddeeefc14f..b09b7027126 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);
     }
 }