From 4486e89c219c0d1b9bd8dfa0b1dd5b0d51ff2268 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Wed, 7 Mar 2018 14:42:05 +0000 Subject: [PATCH] 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 +++++++++++++--- include/sysemu/iothread.h | 1 - include/sysemu/sysemu.h | 1 + iothread.c | 31 ------------------------------- vl.c | 13 +++---------- 5 files changed, 17 insertions(+), 45 deletions(-) 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); } /** diff --git a/include/sysemu/iothread.h b/include/sysemu/iothread.h index 799614ffd2..8a7ac2c528 100644 --- a/include/sysemu/iothread.h +++ b/include/sysemu/iothread.h @@ -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); /* diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h index d24ad09f37..356bfdc1c1 100644 --- a/include/sysemu/sysemu.h +++ b/include/sysemu/sysemu.h @@ -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 */ diff --git a/iothread.c b/iothread.c index 2ec5a3bffe..1b3463cb00 100644 --- a/iothread.c +++ b/iothread.c @@ -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; diff --git a/vl.c b/vl.c index dae986b352..3ef04ce991 100644 --- a/vl.c +++ b/vl.c @@ -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();