On Sat, Sep 29, 2018 at 07:12:00PM +0200, Noralf Trønnes wrote:
> Sergey Suloev reported a crash happening in drm_client_dev_hotplug()
> when fbdev had failed to register.
>
> [ 9.124598] vc4_hdmi 3f902000.hdmi: ASoC: Failed to create component debugfs directory
> [ 9.147667] vc4_hdmi 3f902000.hdmi: vc4-hdmi-hifi <-> 3f902000.hdmi mapping ok
> [ 9.155184] vc4_hdmi 3f902000.hdmi: ASoC: no DMI vendor name!
> [ 9.166544] vc4-drm soc:gpu: bound 3f902000.hdmi (ops vc4_hdmi_ops [vc4])
> [ 9.173840] vc4-drm soc:gpu: bound 3f806000.vec (ops vc4_vec_ops [vc4])
> [ 9.181029] vc4-drm soc:gpu: bound 3f004000.txp (ops vc4_txp_ops [vc4])
> [ 9.188519] vc4-drm soc:gpu: bound 3f400000.hvs (ops vc4_hvs_ops [vc4])
> [ 9.195690] vc4-drm soc:gpu: bound 3f206000.pixelvalve (ops vc4_crtc_ops [vc4])
> [ 9.203523] vc4-drm soc:gpu: bound 3f207000.pixelvalve (ops vc4_crtc_ops [vc4])
> [ 9.215032] vc4-drm soc:gpu: bound 3f807000.pixelvalve (ops vc4_crtc_ops [vc4])
> [ 9.274785] vc4-drm soc:gpu: bound 3fc00000.v3d (ops vc4_v3d_ops [vc4])
> [ 9.290246] [drm] Initialized vc4 0.0.0 20140616 for soc:gpu on minor 0
> [ 9.297464] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
> [ 9.304600] [drm] Driver supports precise vblank timestamp query.
> [ 9.382856] vc4-drm soc:gpu: [drm:drm_fb_helper_fbdev_setup [drm_kms_helper]] *ERROR* Failed to set fbdev configuration
> [ 10.404937] Unable to handle kernel paging request at virtual address 00330a656369768a
> [ 10.441620] [00330a656369768a] address between user and kernel address ranges
> [ 10.449087] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [ 10.454762] Modules linked in: brcmfmac vc4 drm_kms_helper cfg80211 drm rfkill smsc95xx brcmutil usbnet drm_panel_orientation_quirks raspberrypi_hwmon bcm2835_dma crc32_ce pwm_bcm2835 bcm2835_rng virt_dma rng_core i2c_bcm2835 ip_tables x_tables ipv6
> [ 10.477296] CPU: 2 PID: 45 Comm: kworker/2:1 Not tainted 4.19.0-rc5 #3
> [ 10.483934] Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT)
> [ 10.489966] Workqueue: events output_poll_execute [drm_kms_helper]
> [ 10.596515] Process kworker/2:1 (pid: 45, stack limit = 0x000000007e8924dc)
> [ 10.603590] Call trace:
> [ 10.606259] drm_client_dev_hotplug+0x5c/0xb0 [drm]
> [ 10.611303] drm_kms_helper_hotplug_event+0x30/0x40 [drm_kms_helper]
> [ 10.617849] output_poll_execute+0xc4/0x1e0 [drm_kms_helper]
> [ 10.623616] process_one_work+0x1c8/0x318
> [ 10.627695] worker_thread+0x48/0x428
> [ 10.631420] kthread+0xf8/0x128
> [ 10.634615] ret_from_fork+0x10/0x18
> [ 10.638255] Code: 54000220 f9401261 aa1303e0 b4000141 (f9400c21)
> [ 10.644456] ---[ end trace c75b4a4b0e141908 ]---
>
> The reason for this is that drm_fbdev_cma_init() removes the drm_client
> when fbdev registration fails, but it doesn't remove the client from the
> drm_device client list. So the client list now has a pointer that points
> into the unknown and we have a 'use after free' situation.
>
> It was decided during the drm_client API discussions that a client should
> not be allowed to remove itself. This was based on the experience with
> the fbdev/fbcon locking horror show.
>
> So the solution is to just leave the drm_client hanging around doing
> nothing (it doesn't have any callbacks), and let it be removed when
> drm_dev_unregister() is called.
Slightly cleaner solution: Split drm_client_new into drm_client_alloc()
and drm_client_add(). Call the later only when initialization succeeds,
and only _add() will add it to the device list.
But this here gets the job done for -fixes, so:
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
But feel free to respin with the _alloc()/_add() idea.
>
> Fixes: 894a677f4b3e ("drm/cma-helper: Use the generic fbdev emulation")
> Reported-by: Sergey Suloev <ssuloev@xxxxxxxxxxxxx>
> Cc: Stefan Wahren <stefan.wahren@xxxxxxxx>
> Cc: Eric Anholt <eric@xxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
> ---
>
> This bug is in 4.19 so it should go into drm-misc-fixes right?
> (I have never applied a fix before)
Yup.
If you decide to push this, and do the _alloc/add() refactor afterwards
you need to request a backmerge from drm-misc maintainers (since the
refactor should go into drm-misc ofc).
Cheers, Daniel
>
> Noralf.
>
> drivers/gpu/drm/drm_fb_cma_helper.c | 19 +++++++++----------
> 1 file changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
> index 47e0e2f6642d..d82bb4776e3c 100644
> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> @@ -168,22 +168,21 @@ struct drm_fbdev_cma *drm_fbdev_cma_init(struct drm_device *dev,
> fb_helper = &fbdev_cma->fb_helper;
>
> ret = drm_client_new(dev, &fb_helper->client, "fbdev", NULL);
> - if (ret)
> - goto err_free;
> + if (ret) {
> + kfree(fbdev_cma);
> + return ERR_PTR(ret);
> + }
>
> ret = drm_fb_helper_fbdev_setup(dev, fb_helper, &drm_fb_cma_helper_funcs,
> preferred_bpp, max_conn_count);
> if (ret)
> - goto err_client_put;
> + /*
> + * A drm_client is not allowed to remove itself, so it has to
> + * stay around until drm_dev_unregister().
> + */
> + return ERR_PTR(ret);
>
> return fbdev_cma;
> -
> -err_client_put:
> - drm_client_release(&fb_helper->client);
> -err_free:
> - kfree(fbdev_cma);
> -
> - return ERR_PTR(ret);
> }
> EXPORT_SYMBOL_GPL(drm_fbdev_cma_init);
>
> --
> 2.15.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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