drm/vc4: NULL pointer dereference after failed to allocate buffer

[Eric Anholt]

Stefan Wahren <stefan.wahren at i2se.com> writes:

> Hi,
>
> i tried to boot 4.7.0-rc1-next-20160602 with bcm2835_defconfig on a Raspberry Pi
> B.
>
> Unfortunately it crashes with a NULL pointer dereference and many oops
> following:
> ...
> [    2.209373] vc4-drm soc:gpu: bound 20902000.hdmi (ops vc4_hdmi_ops)
> [    2.228303] vc4-drm soc:gpu: bound 20206000.pixelvalve (ops vc4_crtc_ops)
> [    2.247681] vc4-drm soc:gpu: bound 20207000.pixelvalve (ops vc4_crtc_ops)
> [    2.270300] vc4-drm soc:gpu: bound 20807000.pixelvalve (ops vc4_crtc_ops)
> [    2.288902] vc4-drm soc:gpu: bound 20400000.hvs (ops vc4_hvs_ops)
> [    2.307006] vc4-drm soc:gpu: bound 20c00000.v3d (ops vc4_v3d_ops)
> [    2.325069] fb: switching to vc4drmfb from simple
> [    2.341322] Console: switching to colour dummy device 80x30
> [    2.350955] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
> [    2.357821] [drm] No driver support for vblank timestamp query.
> [    2.368495] mmc0: new SDHC card at address 1234
> [    2.374284] mmcblk0: mmc0:1234 SA32G 29.3 GiB
> [    2.381213]  mmcblk0: p1 p2
> [    2.398018] vc4-drm soc:gpu: failed to allocate buffer with size 9216000
> [    2.404912] Unable to handle kernel NULL pointer dereference at virtual
> address 00000000
> [    2.413070] pgd = c0004000
> [    2.415856] [00000000] *pgd=00000000
> [    2.419501] Internal error: Oops: 80000005 [#1] ARM
> [    2.424425] CPU: 0 PID: 6 Comm: kworker/u2:0 Not tainted
> 4.7.0-rc1-next-20160602+ #2
> [    2.432214] Hardware name: BCM2835
> [    2.435677] Workqueue: deferwq deferred_probe_work_func
> [    2.440948] task: cb8957c0 ti: cb8b2000 task.ti: cb8b2000
> [    2.446378] PC is at 0x0
> [    2.448953] LR is at drm_gem_cma_create+0xf0/0x108

Figure out where in drm_gem_cma_create() you are?  -next kernels have
been working for me on Pi 2s and 3s, and jumping to a NULL seems
surprising for that function.
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