FAILED: patch "[PATCH] drm/mediatek: Correctly free sg_table in gem prime vmap" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x dcc583c225e659d5da34b4ad83914fd6b51e3dbf
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023102025-copious-thud-be0f@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From dcc583c225e659d5da34b4ad83914fd6b51e3dbf Mon Sep 17 00:00:00 2001
From: Chen-Yu Tsai <[email protected]>
Date: Wed, 4 Oct 2023 16:32:24 +0800
Subject: [PATCH] drm/mediatek: Correctly free sg_table in gem prime vmap

The MediaTek DRM driver implements GEM PRIME vmap by fetching the sg_table for the object, iterating through the pages, and then vmapping them. In essence, unlike the GEM DMA helpers which vmap when the object is first created or imported, the MediaTek version does it on request.

Unfortunately, the code never correctly frees the sg_table contents. This results in a kernel memory leak. On a Hayato device with a text console on the internal display, this results in the system running out of memory in a few days from all the console screen cursor updates.

Add sg_free_table() to correctly free the contents of the sg_table. This was missing despite explicitly required by mtk_gem_prime_get_sg_table().

Also move the "out" shortcut label to after the kfree() call for the sg_table. Having sg_free_table() together with kfree() makes more sense. The shortcut is only used when the object already has a kernel address, in which case the pointer is NULL and kfree() does nothing. Hence this change causes no functional change.

index 9f364df52478..0e0a41b2f57f 100644
@@ -239,6 +239,7 @@ int mtk_drm_gem_prime_vmap(struct drm_gem_object *obj, struct iosys_map *map)
 	npages = obj->size >> PAGE_SHIFT;
 	mtk_gem->pages = kcalloc(npages, sizeof(*mtk_gem->pages), GFP_KERNEL);
 	if (!mtk_gem->pages) {
+		sg_free_table(sgt);
 		kfree(sgt);
 		return -ENOMEM;
 	}

@@ -248,12 +249,15 @@ int mtk_drm_gem_prime_vmap(struct drm_gem_object *obj, struct iosys_map *map)
 	mtk_gem->kvaddr = vmap(mtk_gem->pages, npages, VM_MAP,
 			       pgprot_writecombine(PAGE_KERNEL));
 	if (!mtk_gem->kvaddr) {
+		sg_free_table(sgt);
 		kfree(sgt);
 		kfree(mtk_gem->pages);
 		return -ENOMEM;
 	}
-out:
+	sg_free_table(sgt);
 	kfree(sgt);
+
+out:
 	iosys_map_set_vaddr(map, mtk_gem->kvaddr);
 
 	return 0;