Re: [Qemu-devel] [PATCH] use broadcast on qemu_pause_cond

[Paolo Bonzini <pbonzini@redhat.com>]

On 25/01/2016 11:08, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Jiri saw a hang on pause_all_vcpus called from postcopy_start,
> where the cpus are all apparently stopped ('stopped' flag set)
> but pause_all_vcpus is still stuck on a cond_wait on qemu_paused_cond.
> We suspect this is happening if a qmp_stop is called at about the
> same time as the postcopy code calls that pause_all_vcpus;
> although they both should have the main lock held, Paolo spotted
> the cond_wait unlocks the global lock so perhaps they both
> could end up waiting at the same time?
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Reported-by: Jiri Denemark <jdenemar@redhat.com>
> ---
>  cpus.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/cpus.c b/cpus.c
> index 3efff6b..1e97cc4 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -986,7 +986,7 @@ static void qemu_wait_io_event_common(CPUState *cpu)
>      if (cpu->stop) {
>          cpu->stop = false;
>          cpu->stopped = true;
> -        qemu_cond_signal(&qemu_pause_cond);
> +        qemu_cond_broadcast(&qemu_pause_cond);
>      }
>      flush_queued_work(cpu);
>      cpu->thread_kicked = false;
> @@ -1396,7 +1396,7 @@ void cpu_stop_current(void)
>          current_cpu->stop = false;
>          current_cpu->stopped = true;
>          cpu_exit(current_cpu);
> -        qemu_cond_signal(&qemu_pause_cond);
> +        qemu_cond_broadcast(&qemu_pause_cond);
>      }
>  }
>  
> 

Thanks, queued.

Paolo