linux-kernel - Re: [PATCH 3/7] vfio/pci: Use vfio_device_unmap_mapping

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Date:   Thu, 5 Aug 2021 22:04:18 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        peterx@...hat.com
Subject: Re: [PATCH 3/7] vfio/pci: Use vfio_device_unmap_mapping_range()

On Thu, Aug 05, 2021 at 11:07:35AM -0600, Alex Williamson wrote:
> @@ -2281,15 +2143,13 @@ static int vfio_pci_try_zap_and_vma_lock_cb(struct pci_dev *pdev, void *data)
>  
>  	vdev = container_of(device, struct vfio_pci_device, vdev);
>  
> -	/*
> -	 * Locking multiple devices is prone to deadlock, runaway and
> -	 * unwind if we hit contention.
> -	 */
> -	if (!vfio_pci_zap_and_vma_lock(vdev, true)) {
> +	if (!down_write_trylock(&vdev->memory_lock)) {
>  		vfio_device_put(device);
>  		return -EBUSY;
>  	}

Now that this is simplified so much, I wonder if we can drop the
memory_lock and just use the dev_set->lock?

That avoids the whole down_write_trylock thing and makes it much more
understandable?

Jason