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drm/i915/frontbuffer: Move bo refcounting intel_frontbuffer_{get,release}()

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Currently xe's intel_frontbuffer implementation forgets to
hold a reference on the bo. This makes the entire thing
extremely fragile as the cleanup order now depends on bo
references held by other things
(namely intel_fb_bo_framebuffer_fini()).

Move the bo refcounting to intel_frontbuffer_{get,release}()
so that both i915 and xe do this the same way.

I first tried to fix this by having xe do the refcounting
from its intel_bo_set_frontbuffer() implementation
(which is what i915 does currently), but turns out xe's
drm_gem_object_free() can sleep and thus drm_gem_object_put()
isn't safe to call while we hold fb_tracking.lock.

Fixes: 10690b8a49 ("drm/i915/display: Add intel_fb_bo_framebuffer_fini")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20251003145734.7634-2-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
This commit is contained in:
Ville Syrjälä
2025-10-03 17:57:30 +03:00
parent 76e46dbf80
commit eb4d490729
2 changed files with 9 additions and 3 deletions
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10
drivers/gpu/drm/i915/display/intel_frontbuffer.c
View File

@@ -270,6 +270,8 @@ static void frontbuffer_release(struct kref *ref)
spin_unlock(&display->fb_tracking.lock);
i915_active_fini(&front->write);
drm_gem_object_put(obj);
kfree_rcu(front, rcu);
}
@@ -287,6 +289,8 @@ intel_frontbuffer_get(struct drm_gem_object *obj)
if (!front)
return NULL;
drm_gem_object_get(obj);
front->obj = obj;
kref_init(&front->ref);
atomic_set(&front->bits, 0);
@@ -299,8 +303,12 @@ intel_frontbuffer_get(struct drm_gem_object *obj)
spin_lock(&display->fb_tracking.lock);
cur = intel_bo_set_frontbuffer(obj, front);
spin_unlock(&display->fb_tracking.lock);
if (cur != front)
if (cur != front) {
drm_gem_object_put(obj);
kfree(front);
}
return cur;
}

2
drivers/gpu/drm/i915/gem/i915_gem_object_frontbuffer.h
View File

@@ -89,12 +89,10 @@ i915_gem_object_set_frontbuffer(struct drm_i915_gem_object *obj,
if (!front) {
RCU_INIT_POINTER(obj->frontbuffer, NULL);
drm_gem_object_put(intel_bo_to_drm_bo(obj));
} else if (rcu_access_pointer(obj->frontbuffer)) {
cur = rcu_dereference_protected(obj->frontbuffer, true);
kref_get(&cur->ref);
} else {
drm_gem_object_get(intel_bo_to_drm_bo(obj));
rcu_assign_pointer(obj->frontbuffer, front);
}