drm/nv04/crtc: Bail out if FB is not bound to crtc

This commit resolves a possible 'NULL pointer dereference'
It uses the same approach as radeon, intel and nouveau/nv50

Fixes bug 'Nouveau: Kernel oops when unplugging external monitor'
https://bugs.freedesktop.org/show_bug.cgi?id=40336

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

diff --git a/drivers/gpu/drm/nouveau/nv04_crtc.c b/drivers/gpu/drm/nouveau/nv04_crtc.c
index 118261d..5e45398 100644 (file)
--- a/drivers/gpu/drm/nouveau/nv04_crtc.c
+++ b/drivers/gpu/drm/nouveau/nv04_crtc.c
@@ -781,11 +781,20 @@ nv04_crtc_do_mode_set_base(struct drm_crtc *crtc,
        struct drm_device *dev = crtc->dev;
        struct drm_nouveau_private *dev_priv = dev->dev_private;
        struct nv04_crtc_reg *regp = &dev_priv->mode_reg.crtc_reg[nv_crtc->index];
-       struct drm_framebuffer *drm_fb = nv_crtc->base.fb;
-       struct nouveau_framebuffer *fb = nouveau_framebuffer(drm_fb);
+       struct drm_framebuffer *drm_fb;
+       struct nouveau_framebuffer *fb;
        int arb_burst, arb_lwm;
        int ret;
 
+       NV_DEBUG_KMS(dev, "index %d\n", nv_crtc->index);
+
+       /* no fb bound */
+       if (!atomic && !crtc->fb) {
+               NV_DEBUG_KMS(dev, "No FB bound\n");
+               return 0;
+       }
+
+
        /* If atomic, we want to switch to the fb we were passed, so
         * now we update pointers to do that.  (We don't pin; just
         * assume we're already pinned and update the base address.)
@@ -794,6 +803,8 @@ nv04_crtc_do_mode_set_base(struct drm_crtc *crtc,
                drm_fb = passed_fb;
                fb = nouveau_framebuffer(passed_fb);
        } else {
+               drm_fb = crtc->fb;
+               fb = nouveau_framebuffer(crtc->fb);
                /* If not atomic, we can go ahead and pin, and unpin the
                 * old fb we were passed.
                 */