Re: [PATCH v2] qemu: send stop event after bdrv_flush_all

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Dec 05, 2023 at 01:48:26AM -0500, tianren@smartx.com wrote:
> From: Tianren Zhang <tianren@smartx.com>
> 
> The stop process is not finished until bdrv_flush_all
> is done. Some users (e.g., libvirt) detect the STOP
> event and invokes some lock release logic to revoke
> the disk lock held by current qemu when such event is
> emitted. In such case, if the bdrv_flush_all is after
> the stop event, it's possible that the disk lock is
> released while the qemu is still waiting for I/O.
> Therefore, it's better to have the stop event generated
> after the whole stop process is done, so we can
> guarantee to users that the stop process is finished
> when they get the STOP event.
>
> Change-Id: Ia2f95cd55edfdeb71ee2e04005ac216cfabffa22

Please don't include this in commit messages for patches posted.
QEMU does not use Gerrit and so this is irrelevant to upstream.

> Signed-off-by: Tianren Zhang <tianren@smartx.com>
> ---
> v2: do not call runstate_is_running twice
> ---
>  system/cpus.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

> 
> diff --git a/system/cpus.c b/system/cpus.c
> index a444a747f0..49af0f92b5 100644
> --- a/system/cpus.c
> +++ b/system/cpus.c
> @@ -262,21 +262,24 @@ void cpu_interrupt(CPUState *cpu, int mask)
>  static int do_vm_stop(RunState state, bool send_stop)
>  {
>      int ret = 0;
> +    bool do_send_stop = false;
>  
>      if (runstate_is_running()) {
>          runstate_set(state);
>          cpu_disable_ticks();
>          pause_all_vcpus();
>          vm_state_notify(0, state);
> -        if (send_stop) {
> -            qapi_event_send_stop();
> -        }
> +        do_send_stop = send_stop;
>      }
>  
>      bdrv_drain_all();
>      ret = bdrv_flush_all();
>      trace_vm_stop_flush_all(ret);
>  
> +    if (do_send_stop) {
> +        qapi_event_send_stop();
> +    }
> +
>      return ret;
>  }

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|