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 <stable@xxxxxxxxxxxxxxx>.
Possible dependencies:
09bf649a7457 ("drm/shmem-helper: Avoid vm_open error paths")
526408357318 ("drm/shmem-helpers: Ensure get_pages is not called on imported dma-buf")
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 09bf649a74573cb596e211418a4f8008f265c5a9 Mon Sep 17 00:00:00 2001
From: Rob Clark <robdclark@xxxxxxxxxxxx>
Date: Wed, 30 Nov 2022 10:57:48 -0800
Subject: [PATCH] drm/shmem-helper: Avoid vm_open error paths
vm_open() is not allowed to fail. Fortunately we are guaranteed that
the pages are already pinned, thanks to the initial mmap which is now
being cloned into a forked process, and only need to increment the
refcnt. So just increment it directly. Previously if a signal was
delivered at the wrong time to the forking process, the
mutex_lock_interruptible() could fail resulting in the pages_use_count
not being incremented.
Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20221130185748.357410-3-robdclark@xxxxxxxxx
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 3b7b71391a4c..b602cd72a120 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -571,12 +571,20 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
{
struct drm_gem_object *obj = vma->vm_private_data;
struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
- int ret;
WARN_ON(shmem->base.import_attach);
- ret = drm_gem_shmem_get_pages(shmem);
- WARN_ON_ONCE(ret != 0);
+ mutex_lock(&shmem->pages_lock);
+
+ /*
+ * We should have already pinned the pages when the buffer was first
+ * mmap'd, vm_open() just grabs an additional reference for the new
+ * mm the vma is getting copied into (ie. on fork()).
+ */
+ if (!WARN_ON_ONCE(!shmem->pages_use_count))
+ shmem->pages_use_count++;
+
+ mutex_unlock(&shmem->pages_lock);
drm_gem_vm_open(vma);
}
