Re: [PATCH v2 7/9] cpus: Introduce qemu_mutex_unlock_iothread_prepare()

[David Hildenbrand]

On 23.07.21 21:34, Peter Xu wrote:
> The prepare function before unlocking BQL.  There're only three places that can
> release the BQL: unlock(), cond_wait() or cond_timedwait().
>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>   softmmu/cpus.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/softmmu/cpus.c b/softmmu/cpus.c
> index 9131f77f87..6085f8edbe 100644
> --- a/softmmu/cpus.c
> +++ b/softmmu/cpus.c
> @@ -66,6 +66,10 @@
>   
>   static QemuMutex qemu_global_mutex;
>   
> +static void qemu_mutex_unlock_iothread_prepare(void)
> +{
> +}
> +
>   bool cpu_is_stopped(CPUState *cpu)
>   {
>       return cpu->stopped || !runstate_is_running();
> @@ -523,16 +527,19 @@ void qemu_mutex_unlock_iothread(void)
>   {
>       g_assert(qemu_mutex_iothread_locked());
>       iothread_locked = false;
> +    qemu_mutex_unlock_iothread_prepare();
>       qemu_mutex_unlock(&qemu_global_mutex);
>   }
>   
>   void qemu_cond_wait_iothread(QemuCond *cond)
>   {
> +    qemu_mutex_unlock_iothread_prepare();
>       qemu_cond_wait(cond, &qemu_global_mutex);
>   }
>   
>   void qemu_cond_timedwait_iothread(QemuCond *cond, int ms)
>   {
> +    qemu_mutex_unlock_iothread_prepare();
>       qemu_cond_timedwait(cond, &qemu_global_mutex, ms);
>   }
>   

I'd squash this patch into the next one.

I don't quite like the function name, but don't really have a better 
suggestion .... maybe qemu_mutex_might_unlock_iothread(), similar to 
might_sleep() or might_fault() in the kernel. (although here it's pretty 
clear and not a "might"; could be useful in other context where we might 
conditionally unlock the BQL at some point in the future, though)

--
Thanks,

David / dhildenb