Re: [PATCH v2 3/7] vfio: Introduce interface to flush virqfd inject workqueue

[Eric Auger]

On 3/9/24 00:05, Alex Williamson wrote:
> In order to synchronize changes that can affect the thread callback,
> introduce an interface to force a flush of the inject workqueue.  The
> irqfd pointer is only valid under spinlock, but the workqueue cannot
> be flushed under spinlock.  Therefore the flush work for the irqfd is
> queued under spinlock.  The vfio_irqfd_cleanup_wq workqueue is re-used
> for queuing this work such that flushing the workqueue is also ordered
> relative to shutdown.
>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>

Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>

Eric
> ---
>  drivers/vfio/virqfd.c | 21 +++++++++++++++++++++
>  include/linux/vfio.h  |  2 ++
>  2 files changed, 23 insertions(+)
>
> diff --git a/drivers/vfio/virqfd.c b/drivers/vfio/virqfd.c
> index 29c564b7a6e1..532269133801 100644
> --- a/drivers/vfio/virqfd.c
> +++ b/drivers/vfio/virqfd.c
> @@ -101,6 +101,13 @@ static void virqfd_inject(struct work_struct *work)
>  		virqfd->thread(virqfd->opaque, virqfd->data);
>  }
>  
> +static void virqfd_flush_inject(struct work_struct *work)
> +{
> +	struct virqfd *virqfd = container_of(work, struct virqfd, flush_inject);
> +
> +	flush_work(&virqfd->inject);
> +}
> +
>  int vfio_virqfd_enable(void *opaque,
>  		       int (*handler)(void *, void *),
>  		       void (*thread)(void *, void *),
> @@ -124,6 +131,7 @@ int vfio_virqfd_enable(void *opaque,
>  
>  	INIT_WORK(&virqfd->shutdown, virqfd_shutdown);
>  	INIT_WORK(&virqfd->inject, virqfd_inject);
> +	INIT_WORK(&virqfd->flush_inject, virqfd_flush_inject);
>  
>  	irqfd = fdget(fd);
>  	if (!irqfd.file) {
> @@ -213,3 +221,16 @@ void vfio_virqfd_disable(struct virqfd **pvirqfd)
>  	flush_workqueue(vfio_irqfd_cleanup_wq);
>  }
>  EXPORT_SYMBOL_GPL(vfio_virqfd_disable);
> +
> +void vfio_virqfd_flush_thread(struct virqfd **pvirqfd)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&virqfd_lock, flags);
> +	if (*pvirqfd && (*pvirqfd)->thread)
> +		queue_work(vfio_irqfd_cleanup_wq, &(*pvirqfd)->flush_inject);
> +	spin_unlock_irqrestore(&virqfd_lock, flags);
> +
> +	flush_workqueue(vfio_irqfd_cleanup_wq);
> +}
> +EXPORT_SYMBOL_GPL(vfio_virqfd_flush_thread);
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 89b265bc6ec3..8b1a29820409 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -356,6 +356,7 @@ struct virqfd {
>  	wait_queue_entry_t		wait;
>  	poll_table		pt;
>  	struct work_struct	shutdown;
> +	struct work_struct	flush_inject;
>  	struct virqfd		**pvirqfd;
>  };
>  
> @@ -363,5 +364,6 @@ int vfio_virqfd_enable(void *opaque, int (*handler)(void *, void *),
>  		       void (*thread)(void *, void *), void *data,
>  		       struct virqfd **pvirqfd, int fd);
>  void vfio_virqfd_disable(struct virqfd **pvirqfd);
> +void vfio_virqfd_flush_thread(struct virqfd **pvirqfd);
>  
>  #endif /* VFIO_H */