Re: [Qemu-devel] [PATCH] iothread: Stop threads before main() quits

[Paolo Bonzini]

On 08/09/2016 11:28, Fam Zheng wrote:
> Right after main_loop ends, we release various things but keep iothread
> alive. The latter is not prepared to the sudden change of resources.
> 
> Specifically, after bdrv_close_all(), virtio-scsi dataplane get a
> surprise at the empty BlockBackend:
> 
> (gdb) bt
>     at /usr/src/debug/qemu-2.6.0/hw/scsi/virtio-scsi.c:543
>     at /usr/src/debug/qemu-2.6.0/hw/scsi/virtio-scsi.c:577
> 
> It is because the d->conf.blk->root is set to NULL, then
> blk_get_aio_context() returns qemu_aio_context, whereas s->ctx is still
> pointing to the iothread:
> 
>     hw/scsi/virtio-scsi.c:543:
> 
>     if (s->dataplane_started) {
>         assert(blk_get_aio_context(d->conf.blk) == s->ctx);
>     }
> 
> To fix this, let's stop iothreads before doing bdrv_close_all().
> 
> Cc: address@hidden
> Signed-off-by: Fam Zheng <address@hidden>
> ---
>  include/sysemu/iothread.h |  1 +
>  iothread.c                | 24 ++++++++++++++++++++----
>  vl.c                      |  2 ++
>  3 files changed, 23 insertions(+), 4 deletions(-)
> 
> diff --git a/include/sysemu/iothread.h b/include/sysemu/iothread.h
> index 2eefea1..68ac2de 100644
> --- a/include/sysemu/iothread.h
> +++ b/include/sysemu/iothread.h
> @@ -35,5 +35,6 @@ typedef struct {
>  
>  char *iothread_get_id(IOThread *iothread);
>  AioContext *iothread_get_aio_context(IOThread *iothread);
> +void iothread_stop_all(void);
>  
>  #endif /* IOTHREAD_H */
> diff --git a/iothread.c b/iothread.c
> index f183d38..fb08a60 100644
> --- a/iothread.c
> +++ b/iothread.c
> @@ -54,16 +54,25 @@ static void *iothread_run(void *opaque)
>      return NULL;
>  }
>  
> -static void iothread_instance_finalize(Object *obj)
> +static int iothread_stop(Object *object, void *opaque)
>  {
> -    IOThread *iothread = IOTHREAD(obj);
> +    IOThread *iothread;
>  
> -    if (!iothread->ctx) {
> -        return;
> +    iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
> +    if (!iothread || !iothread->ctx) {
> +        return 0;
>      }
>      iothread->stopping = true;
>      aio_notify(iothread->ctx);
>      qemu_thread_join(&iothread->thread);
> +    return 0;
> +}
> +
> +static void iothread_instance_finalize(Object *obj)
> +{
> +    IOThread *iothread = IOTHREAD(obj);
> +
> +    iothread_stop(obj, NULL);
>      qemu_cond_destroy(&iothread->init_done_cond);
>      qemu_mutex_destroy(&iothread->init_done_lock);
>      aio_context_unref(iothread->ctx);
> @@ -174,3 +183,10 @@ IOThreadInfoList *qmp_query_iothreads(Error **errp)
>      object_child_foreach(container, query_one_iothread, &prev);
>      return head;
>  }
> +
> +void iothread_stop_all(void)
> +{
> +    Object *container = object_get_objects_root();
> +
> +    object_child_foreach(container, iothread_stop, NULL);
> +}
> diff --git a/vl.c b/vl.c
> index ee557a1..6a218ce 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -121,6 +121,7 @@ int main(int argc, char **argv)
>  #include "crypto/init.h"
>  #include "sysemu/replay.h"
>  #include "qapi/qmp/qerror.h"
> +#include "sysemu/iothread.h"
>  
>  #define MAX_VIRTIO_CONSOLES 1
>  #define MAX_SCLP_CONSOLES 1
> @@ -4616,6 +4617,7 @@ int main(int argc, char **argv, char **envp)
>      trace_init_vcpu_events();
>      main_loop();
>      replay_disable_events();
> +    iothread_stop_all();
>  
>      bdrv_close_all();
>      pause_all_vcpus();
> 

Reviewed-by: Paolo Bonzini <address@hidden>

Paolo