Re: [PATCH v1 9/9] drm/panthor: Add a GEM shrinker

[Boris Brezillon <boris.brezillon@collabora.com>]

Hi Akash,

On Wed, 28 Jan 2026 11:21:43 +0000
Akash Goel <akash.goel@arm.com> wrote:

> Sorry I have a doubt.
> 
> Should we update the panthor_gem_sync() function to ensure pages can't 
> get reclaimed whlilst they are being synced ?.
> 
> panthor_ioctl_bo_sync() takes a reference on the BO before calling 
> panthor_gem_sync(). But I think due to this patch, the backking pages 
> can get released in the middle of sync loop.
> 
> 	sgt = panthor_gem_get_dev_sgt(bo);
> 	if (IS_ERR(sgt))
> 		return PTR_ERR(sgt);
> 	for_each_sgtable_dma_sg(sgt, sgl, count) {
> 		dma_addr_t paddr = sg_dma_address(sgl);
> 		size_t len = sg_dma_len(sgl);
> 
> 		dma_sync_single_for_device();
> 		dma_sync_single_for_cpu();
> 	}
> 
> 
> Please can you confirm.

I think you're right. We either need to pin/unpin around a sync
operation, or we need to take the resv lock to make sure the GEM is not
reclaimed while we do that. It probably makes sense to do the latter,
since we don't want to prematurely pull back the data from the swap
just to synchronize CPU accesses (the
dma_unmap_sgtable() in panthor_gem_dev_map_cleanup_locked() should have
synchronized things for us on a swapout).

I'll fix that before posting a v2.

Thanks,

Boris