From 4486e89c219c0d1b9bd8dfa0b1dd5b0d51ff2268 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Wed, 7 Mar 2018 14:42:05 +0000 Subject: vl: introduce vm_shutdown() Commit 00d09fdbbae5f7864ce754913efc84c12fdf9f1a ("vl: pause vcpus before stopping iothreads") and commit dce8921b2baaf95974af8176406881872067adfa ("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 Cc: Kevin Wolf Signed-off-by: Stefan Hajnoczi Reviewed-by: Fam Zheng Acked-by: Paolo Bonzini Message-id: 20180307144205.20619-5-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi --- cpus.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) (limited to 'cpus.c') diff --git a/cpus.c b/cpus.c index 9bcff7d63c..d8fe90eafe 100644 --- a/cpus.c +++ b/cpus.c @@ -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); } /** -- cgit v1.2.3-55-g7522