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Subject[PATCH] drm/udl: add enable/disable_vblank stubs
vblank_disable_and_save calls the driver's disable_vblank hook unconditionally,
which crashes the udl driver since it doesn't implement it. Fix this by adding
stub implementations of these functions identical to the qxl ones.

usb 5-1: USB disconnect, device number 2
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [< (null)>] (null)
PGD 3bc23d067 PUD 3bc0fc067 PMD 0
Oops: 0010 [#1] PREEMPT SMP
Modules linked in: udlfb fb_sys_fops nvidia(PO) udl drm_kms_helper drm
syscopyarea sysfillrect sysimgblt netconsole cfg80211
joydev mousedev nls_iso8859_1 nls_cp437 vfat fat coretemp
intel_rapl eeepc_wmi asus_wmi sparse_keymap led_class
rfkill hwmon iosf_mbi x86_pkg_temp_thermal intel_powerclamp
iTCO_wdt iTCO_vendor_support evdev kvm crct10dif_pclmul
crc32_pclmul ghash_clmulni_intel aesni_intel mac_hid
tpm_infineon aes_x86_64 lrw gf128mul e1000e glue_helper
ablk_helper cryptd mxm_wmi tpm_tis processor psmouse ptp
serio_raw tpm snd_hda_codec_hdmi i2c_i801 i2c_core lpc_ich
pps_core pcspkr snd_hda_codec_realtek snd_hda_codec_generic
mei_me mei snd_hda_intel snd_hda_controller snd_hda_codec
snd_hwdep snd_pcm snd_timer snd ie31200_edac edac_core
soundcore thermal shpchp battery video wmi button fan
sch_fq_codel nfs lockd grace sunrpc fscache btrfs xor
raid6_pq hid_generic usbhid hid sd_mod atkbd libps2 ahci
libahci crc32c_intel xhci_pci libata ehci_pci xhci_hcd
ehci_hcd scsi_mod usbcore usb_common i8042 serio [last
unloaded: drm]
CPU: 2 PID: 2044 Comm: Xorg.bin Tainted: P O 3.19.0-1-agp #1
Hardware name: System manufacturer System Product Name/P8Z77-V, BIOS 2104 08/13/2013
task: ffff8803f99d27c0 ti: ffff8803bc1c4000 task.ti: ffff8803bc1c4000
RIP: 0010:[<0000000000000000>] [< (null)>] (null)
RSP: 0018:ffff8803bc1c7d00 EFLAGS: 00010046
RAX: ffffffffa06d0140 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 000000000000cee6 RSI: 0000000000000000 RDI: ffff8804037c3000
RBP: ffff8803bc1c7d88 R08: 000000000047b69a R09: 0000000000000000
R10: ffffffffa06de187 R11: 0000000000003246 R12: ffff880403d74540
R13: 0000000000000003 R14: ffff8804037c3000 R15: ffff8803bc32eac8
FS: 00007f7f4753a900(0000) GS:ffff88041ec80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000003bc240000 CR4: 00000000001407e0
ffffffffa06e06da ffff8803bc1c7d38 0000000000000000 0000000000000082
ffff8804037c3188 ffff8803bc1c7d40 0000000000000282 ffff8803bc1c7d68
0000000000000106 000000000000cee6 00000000f69756fa ffff880403d74580
Call Trace:
[<ffffffffa06e06da>] ? vblank_disable_and_save+0x9a/0x200 [drm]
[<ffffffffa06e2205>] drm_vblank_cleanup+0x65/0xb0 [drm]
[<ffffffffa06cc338>] udl_driver_unload+0x18/0x50 [udl]
[<ffffffffa06e3f2d>] drm_dev_unregister+0x2d/0xb0 [drm]
[<ffffffffa06e41e7>] drm_put_dev+0x27/0x70 [drm]
[<ffffffffa06de237>] drm_release+0x347/0x520 [drm]
[<ffffffff811d357f>] __fput+0x9f/0x200
[<ffffffff811d372e>] ____fput+0xe/0x10
[<ffffffff8108fc87>] task_work_run+0xb7/0xf0
[<ffffffff81015d35>] do_notify_resume+0x95/0xa0
[<ffffffff8155f060>] int_signal+0x12/0x17
Code: Bad RIP value.
RIP [< (null)>] (null)
RSP <ffff8803bc1c7d00>
CR2: 0000000000000000
---[ end trace e0b184ca053571af ]---

Reported-by: Thomas Meyer <>
Signed-off-by: Aaron Plattner <>
Daniel, it looks like your change "[5/5] drm/irq: Don't call
->get_vblank_counter directly from irq_uninstall/cleanup" masks the immediate
problem, but it's not clear to me whether that's just because I didn't manage to
trigger any of the new vblank stuff, or whether your change really fixes it. It
does seem like these vblank functions are intended to be called unconditionally.

drivers/gpu/drm/udl/udl_drv.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
index d5728ec85254..5bacb556b0f5 100644
--- a/drivers/gpu/drm/udl/udl_drv.c
+++ b/drivers/gpu/drm/udl/udl_drv.c
@@ -16,6 +16,20 @@ static int udl_driver_set_busid(struct drm_device *d, struct drm_master *m)
return 0;

+static u32 udl_noop_get_vblank_counter(struct drm_device *dev, int crtc)
+ return dev->vblank[crtc].count.counter;
+static int udl_noop_enable_vblank(struct drm_device *dev, int crtc)
+ return 0;
+static void udl_noop_disable_vblank(struct drm_device *dev, int crtc)
static const struct vm_operations_struct udl_gem_vm_ops = {
.fault = udl_gem_fault,
.open = drm_gem_vm_open,
@@ -42,6 +56,10 @@ static struct drm_driver driver = {
.unload = udl_driver_unload,
.set_busid = udl_driver_set_busid,

+ .get_vblank_counter = udl_noop_get_vblank_counter,
+ .enable_vblank = udl_noop_enable_vblank,
+ .disable_vblank = udl_noop_disable_vblank,
/* gem hooks */
.gem_free_object = udl_gem_free_object,
.gem_vm_ops = &udl_gem_vm_ops,

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