drm/panfrost: Fix the error path in panfrost_mmu_map_fault_addr()

Subject: [PATCH] drm/panfrost: Fix the error path in
 panfrost_mmu_map_fault_addr()

If some the pages or sgt allocation failed, we shouldn't release the
pages ref we got earlier, otherwise we will end up with unbalanced
get/put_pages() calls. We should instead leave everything in place
and let the BO release function deal with extra cleanup when the object
is destroyed, or let the fault handler try again next time it's called.

Fixes: 187d292 ("drm/panfrost: Add support for GPU heap allocations")
Cc: <stable@vger.kernel.org>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Co-developed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240105184624.508603-18-dmitry.osipenko@collabora.com

Author: bbrezillon

drivers/gpu/drm/panfrost/panfrost_mmu.c

@@ -502,19 +502,26 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 	mapping_set_unevictable(mapping);
 
 	for (i = page_offset; i < page_offset + NUM_FAULT_PAGES; i++) {
+		/* Can happen if the last fault only partially filled this
+		 * section of the pages array before failing. In that case
+		 * we skip already filled pages.
+		 */
+		if (pages[i])
+			continue;
+
 		pages[i] = shmem_read_mapping_page(mapping, i);
 		if (IS_ERR(pages[i])) {
 			ret = PTR_ERR(pages[i]);
 			pages[i] = NULL;
-			goto err_pages;
+			goto err_unlock;
 		}
 	}
 
 	sgt = &bo->sgts[page_offset / (SZ_2M / PAGE_SIZE)];
 	ret = sg_alloc_table_from_pages(sgt, pages + page_offset,
 					NUM_FAULT_PAGES, 0, SZ_2M, GFP_KERNEL);
 	if (ret)
-		goto err_pages;
+		goto err_unlock;
 
 	ret = dma_map_sgtable(pfdev->dev, sgt, DMA_BIDIRECTIONAL, 0);
 	if (ret)
@@ -537,8 +544,6 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 
 err_map:
 	sg_free_table(sgt);
-err_pages:
-	drm_gem_shmem_put_pages(&bo->base);
 err_unlock:
 	dma_resv_unlock(obj->resv);
 err_bo: