On Fri, Nov 20, 2020 at 10:15:57PM +0000, Chrisanthus, Anitha wrote:
> Hi Dan,
> I see the problem now, thanks for the patch.
>
> > -----Original Message-----
> > From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > Sent: Friday, November 20, 2020 12:11 AM
> > To: Chrisanthus, Anitha <anitha.chrisanthus@xxxxxxxxx>
> > Cc: Dea, Edmund J <edmund.j.dea@xxxxxxxxx>; David Airlie <airlied@xxxxxxxx>;
> > Daniel Vetter <daniel@xxxxxxxx>; Sam Ravnborg <sam@xxxxxxxxxxxx>; dri-
> > devel@xxxxxxxxxxxxxxxxxxxxx; kernel-janitors@xxxxxxxxxxxxxxx
> > Subject: [PATCH v2] drm/kmb: Fix possible oops in probe error handling
> >
> > If kmb_dsi_init() fails the "kmb->kmb_dsi" variable is an error pointer.
> > The kernel will Oops when we pass it to kmb_dsi_host_unregister().
> >
> > Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
> > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > ---
> > v2: write a better commit message
> >
> > drivers/gpu/drm/kmb/kmb_drv.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/kmb/kmb_drv.c
> > b/drivers/gpu/drm/kmb/kmb_drv.c
> > index a31a840ce634..8c43b136765c 100644
> > --- a/drivers/gpu/drm/kmb/kmb_drv.c
> > +++ b/drivers/gpu/drm/kmb/kmb_drv.c
> > @@ -504,7 +504,7 @@ static int kmb_probe(struct platform_device *pdev)
> > if (IS_ERR(kmb->kmb_dsi)) {
> > drm_err(&kmb->drm, "failed to initialize DSI\n");
> > ret = PTR_ERR(kmb->kmb_dsi);
> > - goto err_free1;
> > + goto err_clear_drvdata;
> > }
> >
> > kmb->kmb_dsi->dev = &dsi_pdev->dev;
> > @@ -540,8 +540,9 @@ static int kmb_probe(struct platform_device *pdev)
> > drm_crtc_cleanup(&kmb->crtc);
> > drm_mode_config_cleanup(&kmb->drm);
> > err_free1:
> > - dev_set_drvdata(dev, NULL);
> > kmb_dsi_host_unregister(kmb->kmb_dsi);
> > + err_clear_drvdata:
> We still need to unregister the dsi_host that was registered in this call kmb_dsi_host_bridge_init.
> This will require more changes in kmb_dsi_host_unregister and/or separate out mipi_dsi_host_unregister.
> FYI - I will be out all of next week, will be back the next Monday.
Hm... Yes. Now that you point it out, there are several bugs related
to kmb_dsi_host_bridge_init()...
182 void kmb_dsi_host_unregister(struct kmb_dsi *kmb_dsi)
183 {
184 kmb_dsi_clk_disable(kmb_dsi);
185 mipi_dsi_host_unregister(kmb_dsi->host);
^^^^^^^^^^^^^
kmb_dsi->host is dsi_host.
Every user unregisters it, but only the first user registers it. So
if there are multiple users it will be unregistered prematurely. Should
there be a kfree to prevent a leak?
kfree(kmb_dsi->host);
dsi_host = NULL;
186 }
[ snip ]
216 int kmb_dsi_host_bridge_init(struct device *dev)
217 {
218 struct device_node *encoder_node, *dsi_out;
219
220 /* Create and register MIPI DSI host */
221 if (!dsi_host) {
^^^^^^^^
This is only allocated for the first user.
222 dsi_host = kzalloc(sizeof(*dsi_host), GFP_KERNEL);
223 if (!dsi_host)
224 return -ENOMEM;
225
226 dsi_host->ops = &kmb_dsi_host_ops;
227
228 if (!dsi_device) {
229 dsi_device = kzalloc(sizeof(*dsi_device), GFP_KERNEL);
230 if (!dsi_device) {
231 kfree(dsi_host);
^^^^^^^^^^^^^^^
But now it is non-NULL but it is a freed pointer. dsi_host = NULL;
232 return -ENOMEM;
233 }
234 }
235
236 dsi_host->dev = dev;
237 mipi_dsi_host_register(dsi_host);
238 }
239
[ snip ]
482
483 of_node_put(dsi_in);
484 of_node_put(dsi_node);
485 ret = kmb_dsi_host_bridge_init(get_device(&dsi_pdev->dev));
^^^^^^^^^^^^^^^^^^^^^^^^^^
This get_device() needs a matching put_device(). I kind of like to put
the kref_get() calls on their own line so that they're more obvious to
the reader.
get_device(&dsi_pdev->dev);
kmb_dsi_host_bridge_init(&dsi_pdev->dev);
486
487 if (ret == -EPROBE_DEFER) {
488 return -EPROBE_DEFER;
489 } else if (ret) {
490 DRM_ERROR("probe failed to initialize DSI host bridge\n");
491 return ret;
492 }
493
494 /* Create DRM device */
495 kmb = devm_drm_dev_alloc(dev, &kmb_driver,
496 struct kmb_drm_private, drm);
497 if (IS_ERR(kmb))
498 return PTR_ERR(kmb);
On these error paths we would want to unwind using a call to
kmb_dsi_host_unregister().
499
500 dev_set_drvdata(dev, &kmb->drm);
501
502 /* Initialize MIPI DSI */
503 kmb->kmb_dsi = kmb_dsi_init(dsi_pdev);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This is the call where the "kmb_dsi->host = dsi_host;" assignment
actually happens.
504 if (IS_ERR(kmb->kmb_dsi)) {
505 drm_err(&kmb->drm, "failed to initialize DSI\n");
506 ret = PTR_ERR(kmb->kmb_dsi);
507 goto err_free1;
508 }
509
510 kmb->kmb_dsi->dev = &dsi_pdev->dev;
511 kmb->kmb_dsi->pdev = dsi_pdev;
512 ret = kmb_hw_init(&kmb->drm, 0);
It feels like it would be a lot easier if the kmb_dsi_init() and
kmb_dsi_host_bridge_init() functions were combined. Probably the
dsi_host and dsi_device stuff needs to be refcounted?
Anyway, I can't test this stuff and I'm not really familiar with the
driver. Could you fix it and CC me on the fix?
regards,
dan carpenter
