On Tue, Apr 24, 2018 at 6:04 AM, Daniel Vetter daniel@ffwll.ch wrote:
On Fri, Apr 20, 2018 at 09:55:32AM -0400, Sean Paul wrote:
On Fri, Apr 20, 2018 at 01:50:01PM +0200, Emil Lundmark wrote:
This fixes a NULL pointer dereference that can happen if the UDL driver is unloaded before the framebuffer is initialized. This can happen e.g. if the USB device is unplugged right after it was plugged in.
JFYI, in future, if someone makes a suggestion on how to fix a bug, it's good practice to add a Suggested-by tag to give credit.
Reviewed-by: Sean Paul seanpaul@chromium.org
I think a bit more detail in the commit message on why this is even possible would be good. I think it can only happen when you only plug in the udl, without anything connected.
Hehe, I was just reviewing this code internally, so I can answer that one :)
It happens when fbdev is disabled (which is the case for Chrome OS). Even though intialization of the fbdev part is optional (it's done in udlfb_create which is the callback for fb_probe()), the teardown isn't optional (udl_driver_unload -> udl_fbdev_cleanup -> udl_fbdev_destroy).
Note that udl_fbdev_cleanup *tries* to be conditional (you can see it does if (!udl->fbdev)) but that doesn't work, because udl->fbdev is always set during udl_fbdev_init.
Stéphane
In that case fbdev setup will be delayed until something shows up (so we don't pin a too small fb for it, a feature requested by soc people). This can easily be tested: First:
- plug in udl device
- wait a minute or so (to make it clear it's not a race)
- unplug
And then:
- plug in an udl device, but with something connected.
- unplug right away.
I expect that in the first case you'll always blow up, but in the 2nd one you'll never blow up (no matter how fast you unplug).
Cheers, Daniel
Signed-off-by: Emil Lundmark lndmrk@chromium.org
drivers/gpu/drm/udl/udl_fb.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/udl/udl_fb.c b/drivers/gpu/drm/udl/udl_fb.c index 2ebdc6d5a76e..5754e37f741b 100644 --- a/drivers/gpu/drm/udl/udl_fb.c +++ b/drivers/gpu/drm/udl/udl_fb.c @@ -426,9 +426,11 @@ static void udl_fbdev_destroy(struct drm_device *dev, { drm_fb_helper_unregister_fbi(&ufbdev->helper); drm_fb_helper_fini(&ufbdev->helper);
- drm_framebuffer_unregister_private(&ufbdev->ufb.base);
- drm_framebuffer_cleanup(&ufbdev->ufb.base);
- drm_gem_object_put_unlocked(&ufbdev->ufb.obj->base);
- if (ufbdev->ufb.obj) {
drm_framebuffer_unregister_private(&ufbdev->ufb.base);drm_framebuffer_cleanup(&ufbdev->ufb.base);drm_gem_object_put_unlocked(&ufbdev->ufb.obj->base);- }
}
int udl_fbdev_init(struct drm_device *dev)
2.17.0.484.g0c8726318c-goog
-- Sean Paul, Software Engineer, Google / Chromium OS _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
-- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel