Re: [PATCHv3 2/2] kvm: retry nx_huge_page_recovery_thread creation

[Simon Horman <horms@kernel.org>]

On Thu, Feb 27, 2025 at 03:06:31PM -0800, Keith Busch wrote:
> From: Sean Christopherson <seanjc@google.com>
> 
> A VMM may send a signal to its threads while they've entered KVM_RUN. If
> that thread happens to be trying to make the huge page recovery vhost
> task, then it fails with -ERESTARTNOINTR. We need to retry if that
> happens, so call_once needs to be retryable. Make call_once complete
> only if what it called was successful.
> 
> [implemented the kvm user side]
> Signed-off-by: Keith Busch <kbusch@kernel.org>

...

> diff --git a/include/linux/call_once.h b/include/linux/call_once.h
> index 6261aa0b3fb00..ddcfd91493eaa 100644
> --- a/include/linux/call_once.h
> +++ b/include/linux/call_once.h
> @@ -26,20 +26,26 @@ do {									\
>  	__once_init((once), #once, &__key);				\
>  } while (0)
>  
> -static inline void call_once(struct once *once, void (*cb)(struct once *))
> +static inline int call_once(struct once *once, int (*cb)(struct once *))
>  {
> +	int r;
> +
>          /* Pairs with atomic_set_release() below.  */
>          if (atomic_read_acquire(&once->state) == ONCE_COMPLETED)
> -                return;
> +		return 0;
>  
>          guard(mutex)(&once->lock);
>          WARN_ON(atomic_read(&once->state) == ONCE_RUNNING);
>          if (atomic_read(&once->state) != ONCE_NOT_STARTED)
> -                return;
> +                return -EINVAL;

Hi Keith,

A minor nit from my side:

As you are changing this line, and it seems like there will be another
revision of this series anyway, please consider updating the indentation to
use tabs.

>  
>          atomic_set(&once->state, ONCE_RUNNING);
> -        cb(once);
> -        atomic_set_release(&once->state, ONCE_COMPLETED);
> +	r = cb(once);
> +	if (r)
> +		atomic_set(&once->state, ONCE_NOT_STARTED);
> +	else
> +		atomic_set_release(&once->state, ONCE_COMPLETED);
> +	return r;
>  }
>  
>  #endif /* _LINUX_CALL_ONCE_H */
> -- 
> 2.43.5
> 
>