linux-kernel - [PATCH] drm/mediatek: Correctly free sg

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Message-ID: <20231002092051.555479-1-wenst@chromium.org>
Date:   Mon,  2 Oct 2023 17:20:48 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     Chen-Yu Tsai <wenst@...omium.org>, dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org
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().

Fixes: 3df64d7b0a4f ("drm/mediatek: Implement gem prime vmap/vunmap function")
Cc: <stable@...r.kernel.org>
Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
---
Please merge for v6.6 fixes.

Also, I was wondering why the MediaTek DRM driver implements a lot of
the GEM functionality itself, instead of using the GEM DMA helpers.
>From what I could tell, the code closely follows the DMA helpers, except
that it vmaps the buffers only upon request.


 drivers/gpu/drm/mediatek/mtk_drm_gem.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_gem.c b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
index 9f364df52478..297ee090e02e 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
@@ -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;
 	}
@@ -248,11 +249,13 @@ 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);
 	iosys_map_set_vaddr(map, mtk_gem->kvaddr);
 
-- 
2.42.0.582.g8ccd20d70d-goog