vl: introduce vm_shutdown()

Commit 00d09fdbba ("vl: pause vcpus before
stopping iothreads") and commit dce8921b2b
("iothread: Stop threads before main() quits") tried to work around the
fact that emulation was still active during termination by stopping
iothreads.  They suffer from race conditions:
1. virtio_scsi_handle_cmd_vq() racing with iothread_stop_all() hits the
   virtio_scsi_ctx_check() assertion failure because the BDS AioContext
   has been modified by iothread_stop_all().
2. Guest vq kick racing with main loop termination leaves a readable
   ioeventfd that is handled by the next aio_poll() when external
   clients are enabled again, resulting in unwanted emulation activity.

This patch obsoletes those commits by fully disabling emulation activity
when vcpus are stopped.

Use the new vm_shutdown() function instead of pause_all_vcpus() so that
vm change state handlers are invoked too.  Virtio devices will now stop
their ioeventfds, preventing further emulation activity after vm_stop().

Note that vm_stop(RUN_STATE_SHUTDOWN) cannot be used because it emits a
QMP STOP event that may affect existing clients.

It is no longer necessary to call replay_disable_events() directly since
vm_shutdown() does so already.

Drop iothread_stop_all() since it is no longer used.

Cc: Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20180307144205.20619-5-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2018-03-07 14:42:05 +00:00
parent 184b962346
commit 4486e89c21
5 changed files with 17 additions and 45 deletions

16
cpus.c
View File

@ -993,7 +993,7 @@ void cpu_synchronize_all_pre_loadvm(void)
}
}
static int do_vm_stop(RunState state)
static int do_vm_stop(RunState state, bool send_stop)
{
int ret = 0;
@ -1002,7 +1002,9 @@ static int do_vm_stop(RunState state)
pause_all_vcpus();
runstate_set(state);
vm_state_notify(0, state);
qapi_event_send_stop(&error_abort);
if (send_stop) {
qapi_event_send_stop(&error_abort);
}
}
bdrv_drain_all();
@ -1012,6 +1014,14 @@ static int do_vm_stop(RunState state)
return ret;
}
/* Special vm_stop() variant for terminating the process. Historically clients
* did not expect a QMP STOP event and so we need to retain compatibility.
*/
int vm_shutdown(void)
{
return do_vm_stop(RUN_STATE_SHUTDOWN, false);
}
static bool cpu_can_run(CPUState *cpu)
{
if (cpu->stop) {
@ -1994,7 +2004,7 @@ int vm_stop(RunState state)
return 0;
}
return do_vm_stop(state);
return do_vm_stop(state, true);
}
/**

View File

@ -45,7 +45,6 @@ typedef struct {
char *iothread_get_id(IOThread *iothread);
IOThread *iothread_by_id(const char *id);
AioContext *iothread_get_aio_context(IOThread *iothread);
void iothread_stop_all(void);
GMainContext *iothread_get_g_main_context(IOThread *iothread);
/*

View File

@ -56,6 +56,7 @@ void vm_start(void);
int vm_prepare_start(void);
int vm_stop(RunState state);
int vm_stop_force_state(RunState state);
int vm_shutdown(void);
typedef enum WakeupReason {
/* Always keep QEMU_WAKEUP_REASON_NONE = 0 */

View File

@ -101,18 +101,6 @@ void iothread_stop(IOThread *iothread)
qemu_thread_join(&iothread->thread);
}
static int iothread_stop_iter(Object *object, void *opaque)
{
IOThread *iothread;
iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
if (!iothread) {
return 0;
}
iothread_stop(iothread);
return 0;
}
static void iothread_instance_init(Object *obj)
{
IOThread *iothread = IOTHREAD(obj);
@ -333,25 +321,6 @@ IOThreadInfoList *qmp_query_iothreads(Error **errp)
return head;
}
void iothread_stop_all(void)
{
Object *container = object_get_objects_root();
BlockDriverState *bs;
BdrvNextIterator it;
for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
AioContext *ctx = bdrv_get_aio_context(bs);
if (ctx == qemu_get_aio_context()) {
continue;
}
aio_context_acquire(ctx);
bdrv_set_aio_context(bs, qemu_get_aio_context());
aio_context_release(ctx);
}
object_child_foreach(container, iothread_stop_iter, NULL);
}
static gpointer iothread_g_main_context_init(gpointer opaque)
{
AioContext *ctx;

13
vl.c
View File

@ -4722,17 +4722,10 @@ int main(int argc, char **argv, char **envp)
os_setup_post();
main_loop();
replay_disable_events();
/* The ordering of the following is delicate. Stop vcpus to prevent new
* I/O requests being queued by the guest. Then stop IOThreads (this
* includes a drain operation and completes all request processing). At
* this point emulated devices are still associated with their IOThreads
* (if any) but no longer have any work to do. Only then can we close
* block devices safely because we know there is no more I/O coming.
*/
pause_all_vcpus();
iothread_stop_all();
/* No more vcpu or device emulation activity beyond this point */
vm_shutdown();
bdrv_close_all();
res_free();