Re: [patch V2 02/31] genirq/msi: Add mutex for MSI list protection

[Jason Gunthorpe]

On Mon, Dec 06, 2021 at 11:51:05PM +0100, Thomas Gleixner wrote:
> +++ b/kernel/irq/msi.c
> @@ -127,12 +127,37 @@ int msi_setup_device_data(struct device
>  		return -ENOMEM;
>  
>  	INIT_LIST_HEAD(&md->list);
> +	mutex_init(&md->mutex);
>  	dev->msi.data = md;
>  	devres_add(dev, md);
>  	return 0;
>  }
>  
>  /**
> + * msi_lock_descs - Lock the MSI descriptor storage of a device
> + * @dev:	Device to operate on
> + */
> +void msi_lock_descs(struct device *dev)
> +{
> +	if (WARN_ON_ONCE(!dev->msi.data))
> +		return;

Is this useful? Other places that call msi_lock_descs will continue on and deref
null dev->msi anyhow - is the dump from the WARN_ON that much better
than the oops from the null deref here:

> +	mutex_lock(&dev->msi.data->mutex);

?

Honestly, still a bit unclear on what the community consensus is for
using WARN_ON.

Jason