We use the global device inode, shared amongst all files, and not the
user's device filp to provide the backing storage for the mmap. The
vma->vm_file provides a redundant reference that breaks existing
expected behaviour that closing the user's device fd will release the
resources bound to it, if a mmap persists. (Even without the
vma->vm_file, the mmap will persist past the user's fd as the storage is
bound to the device, i.e. our reference is on the object not file.)
Fixes: cc662126b413 ("drm/i915: Introduce DRM_I915_GEM_MMAP_OFFSET")
Closes: https://gitlab.freedesktop.org/drm/intel/issues/919
Signed-off-by: Chris Wilson <[email protected]>
---
drivers/gpu/drm/i915/gem/i915_gem_mman.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index 905527ce2999..20f065e02fe2 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -699,6 +699,7 @@ int i915_gem_mmap(struct file *filp, struct vm_area_struct
*vma)
struct drm_device *dev = priv->minor->dev;
struct i915_mmap_offset *mmo = NULL;
struct drm_gem_object *obj = NULL;
+ struct file *anon;
if (drm_dev_is_unplugged(dev))
return -ENODEV;
@@ -747,9 +748,26 @@ int i915_gem_mmap(struct file *filp, struct vm_area_struct
*vma)
vma->vm_flags &= ~VM_MAYWRITE;
}
+ anon = drm_minor_create_anonfile(dev->primary, vma->vm_file->f_flags);
+ if (IS_ERR(anon)) {
+ drm_gem_object_put_unlocked(obj);
+ return PTR_ERR(anon);
+ }
+
vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
vma->vm_private_data = mmo;
+ /*
+ * We keep the ref on mmo->obj, not vm_file, but we require
+ * vma->vm_file->f_mapping, see vma_link(), for later revocation.
+ * Our userspace is accustomed to having per-file resource cleanup
+ * (i.e. contexts, objects and requests) on their close(fd), which
+ * requires avoiding extraneous references to their filp, hence why
+ * we prefer to use an anonymous file for their mmaps.
+ */
+ fput(vma->vm_file);
+ vma->vm_file = anon;
+
switch (mmo->mmap_type) {
case I915_MMAP_TYPE_WC:
vma->vm_page_prot =
--
2.25.0.rc0
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