[Intel-gfx] [PATCH v3] drm/i915/display: disable HPD workers before display driver unregister

[Andrzej Hajda]

Handling HPD during driver removal is pointless, and can cause different
use-after-free/concurrency issues:
1. Setup of deferred fbdev after fbdev unregistration.
2. Access to DP-AUX after DP-AUX removal.

Below stacktraces of both cases observed on CI:

[272.634530] general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP NOPTI
[272.634536] CPU: 0 PID: 6030 Comm: i915_selftest Tainted: G     U            5.18.0-rc5-CI_DRM_11603-g12dccf4f5eef+ #1
[272.634541] Hardware name: Intel Corporation Raptor Lake Client Platform/RPL-S ADP-S DDR5 UDIMM CRB, BIOS RPLSFWI1.R00.2397.A01.2109300731 09/30/2021
[272.634545] RIP: 0010:fb_do_apertures_overlap.part.14+0x26/0x60
...
[272.634582] Call Trace:
[272.634583]  <TASK>
[272.634585]  do_remove_conflicting_framebuffers+0x59/0xa0
[272.634589]  remove_conflicting_framebuffers+0x2d/0xc0
[272.634592]  remove_conflicting_pci_framebuffers+0xc8/0x110
[272.634595]  drm_aperture_remove_conflicting_pci_framebuffers+0x52/0x70
[272.634604]  i915_driver_probe+0x63a/0xdd0 [i915]

[283.405824] cpu_latency_qos_update_request called for unknown object
[283.405866] WARNING: CPU: 2 PID: 240 at kernel/power/qos.c:296 cpu_latency_qos_update_request+0x2d/0x100
[283.405912] CPU: 2 PID: 240 Comm: kworker/u64:9 Not tainted 5.18.0-rc6-Patchwork_103738v3-g1672d1c43e43+ #1
[283.405915] Hardware name: Intel Corporation Raptor Lake Client Platform/RPL-S ADP-S DDR5 UDIMM CRB, BIOS RPLSFWI1.R00.2397.A01.2109300731 09/30/2021
[283.405916] Workqueue: i915-dp i915_digport_work_func [i915]
[283.406020] RIP: 0010:cpu_latency_qos_update_request+0x2d/0x100
...
[283.406040] Call Trace:
[283.406041]  <TASK>
[283.406044]  intel_dp_aux_xfer+0x60e/0x8e0 [i915]
[283.406131]  ? finish_swait+0x80/0x80
[283.406139]  intel_dp_aux_transfer+0xc5/0x2b0 [i915]
[283.406218]  drm_dp_dpcd_access+0x79/0x130 [drm_display_helper]
[283.406227]  drm_dp_dpcd_read+0xe2/0xf0 [drm_display_helper]
[283.406233]  intel_dp_hpd_pulse+0x134/0x570 [i915]
[283.406308]  ? __down_killable+0x70/0x140
[283.406313]  i915_digport_work_func+0xba/0x150 [i915]

Signed-off-by: Andrzej Hajda <andrzej.hajda at intel.com>
---
Hi all,

This is my Nth attempt to solve some old CI bug[1].
v1: caused issues in kms code [2],
v2: revealed that not only fbdev does not like HPD on removal [3],
v3: lacks drm_kms_helper_poll_disable[4]

Moreover this is quite rare bug, but due to specific configuration
of one of CI machines it appears there very frequently.

[1]: https://gitlab.freedesktop.org/drm/intel/-/issues/5329
[2]: https://patchwork.freedesktop.org/series/103621/
[3]: https://patchwork.freedesktop.org/series/103738/
[4]: https://patchwork.freedesktop.org/series/103811/

Regards
Andrzej
---
 drivers/gpu/drm/i915/display/intel_display.c | 2 ++
 drivers/gpu/drm/i915/display/intel_fbdev.c   | 1 +
 2 files changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index 806d50b302ab92..9c9232da61ff37 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -10584,6 +10584,8 @@ void intel_display_driver_unregister(struct drm_i915_private *i915)
 	if (!HAS_DISPLAY(i915))
 		return;
 
+	intel_hpd_cancel_work(i915);
+	drm_kms_helper_poll_disable(&i915->drm);
 	intel_fbdev_unregister(i915);
 	intel_audio_deinit(i915);
 
diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
index 221336178991f0..908741c3161676 100644
--- a/drivers/gpu/drm/i915/display/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
@@ -308,6 +308,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
 		    i915_ggtt_offset(vma));
 	ifbdev->vma = vma;
 	ifbdev->vma_flags = flags;
+	dump_stack();
 
 	intel_runtime_pm_put(&dev_priv->runtime_pm, wakeref);
 	vga_switcheroo_client_fb_set(pdev, info);
-- 
2.25.1