[PATCH 6/6] drm/exynos: call find_vma with the mmap_sem held

[Davidlohr Bueso]

From: Jonathan Gonzalez V <z...@gnu.org>

Performing vma lookups without taking the mm->mmap_sem is asking
for trouble. While doing the search, the vma in question can be
modified or even removed before returning to the caller. Take the
lock (exclusively) in order to avoid races while iterating through
the vmacache and/or rbtree.

This patch is completely *untested*.

Signed-off-by: Jonathan Gonzalez V <z...@gnu.org>
Signed-off-by: Davidlohr Bueso <davidl...@hp.com>
Cc: Inki Dae <inki....@samsung.com>
Cc: Joonyoung Shim <jy0922.s...@samsung.com>
Cc: David Airlie <airl...@linux.ie>
Cc: dri-de...@lists.freedesktop.org
Cc: linux-samsung-soc@vger.kernel.org
---
 drivers/gpu/drm/exynos/exynos_drm_g2d.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_g2d.c 
b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
index 6c1885e..8001587 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_g2d.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
@@ -467,14 +467,17 @@ static dma_addr_t *g2d_userptr_get_dma_addr(struct 
drm_device *drm_dev,
                goto err_free;
        }
 
+       down_read(&current->mm->mmap_sem);
        vma = find_vma(current->mm, userptr);
        if (!vma) {
+               up_read(&current->mm->mmap_sem);
                DRM_ERROR("failed to get vm region.\n");
                ret = -EFAULT;
                goto err_free_pages;
        }
 
        if (vma->vm_end < userptr + size) {
+               up_read(&current->mm->mmap_sem);
                DRM_ERROR("vma is too small.\n");
                ret = -EFAULT;
                goto err_free_pages;
@@ -482,6 +485,7 @@ static dma_addr_t *g2d_userptr_get_dma_addr(struct 
drm_device *drm_dev,
 
        g2d_userptr->vma = exynos_gem_get_vma(vma);
        if (!g2d_userptr->vma) {
+               up_read(&current->mm->mmap_sem);
                DRM_ERROR("failed to copy vma.\n");
                ret = -ENOMEM;
                goto err_free_pages;
@@ -492,10 +496,12 @@ static dma_addr_t *g2d_userptr_get_dma_addr(struct 
drm_device *drm_dev,
        ret = exynos_gem_get_pages_from_userptr(start & PAGE_MASK,
                                                npages, pages, vma);
        if (ret < 0) {
+               up_read(&current->mm->mmap_sem);
                DRM_ERROR("failed to get user pages from userptr.\n");
                goto err_put_vma;
        }
 
+       up_read(&current->mm->mmap_sem);
        g2d_userptr->pages = pages;
 
        sgt = kzalloc(sizeof(*sgt), GFP_KERNEL);
-- 
1.8.1.4

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