I observed the following crash on my laptop after undocking it:

BUG: unable to handle kernel NULL pointer dereference at 00000000000000e4 IP: i915_hpd_poll_init_work+0x8f/0x100 [i915] PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP Modules linked in: ppp_mppe ppp_async ppp_generic slhc nf_conntrack_pptp nf_conntrack_proto_gre veth ipt_MASQUERADE nf_nat_masquerade_ipv4 nf_conntrack_netlink nfnetlink xfrm_user kvm irqbypass crct10dif_pclmul iwlmvm crc32_pclmul ghash_clmulni_intel mei_wdt iTCO_wdt iTCO_vendor_support mac80211 wmi_bmof pcbc i2c_algo_bit snd_hda_intel drm_kms_helper snd_hd usbcore usb_common i8042 serio vfat fat trusted tpm crc32c_generic crc32c_intel btrfs xor zstd_decompress zstd_compress xxhash raid6_pq CPU: 0 PID: 37 Comm: kworker/0:1 Tainted: G U O 4.14.9-1-ARCH #1 Hardware name: LENOVO 20F9CTO1WW/20F9CTO1WW, BIOS N1CET56W (1.24 ) 04/19/2017 Workqueue: events i915_hpd_poll_init_work [i915] task: ffffa0bd09132dc0 task.stack: ffffb177032b0000 RIP: 0010:i915_hpd_poll_init_work+0x8f/0x100 [i915] RSP: 0018:ffffb177032b3e58 EFLAGS: 00010202 RAX: ffffa0bcf5b2d800 RBX: 0000000000000001 RCX: 0000000000000056 RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffc0a9d8f7 RBP: ffffa0bcf8f1abc0 R08: 0000000000000003 R09: 0000000000000002 R10: ffffa0bcf8f182f8 R11: 0000000000000c00 R12: ffffa0bcf8f18000 R13: 0000000000000000 R14: ffffa0bcf8f181f8 R15: ffffa0bd092843c0 FS: 0000000000000000(0000) GS:ffffa0bd21400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000000000e4 CR3: 0000000157c09002 CR4: 00000000003606f0 Call Trace: process_one_work+0x1db/0x410 worker_thread+0x2b/0x3d0 ? process_one_work+0x410/0x410 kthread+0x118/0x130 ? kthread_create_on_node+0x70/0x70 ret_from_fork+0x1f/0x30 Code: 0f b6 90 a0 04 00 00 48 83 b8 b0 04 00 00 00 88 90 e8 02 00 00 75 dc 84 d2 75 d8 f6 85 70 da ff ff 02 74 cf 48 8b 90 00 04 00 00 <8b> 92 e4 00 00 00 85 d2 74 be 88 98 e8 02 0 RIP: i915_hpd_poll_init_work+0x8f/0x100 [i915] RSP: ffffb177032b3e58 CR2: 00000000000000e4 ---[ end trace 098075e41d0a597e ]---

The values of the registers seems to indicate that it tries to dereference the hpd_pin field of the encoder structure. The value 0xe4 corresponds to the offset of the field hpd_pin in the encoder structure. It appears that encoder->hpd_pin is accessed without checking first that encoder is not NULL. The same issue may happen in intel_hpd_irq_storm_reenable_work(). This patch should fix these issues.

Signed-off-by: Olivier Sobrie olivier@sobrie.be --- drivers/gpu/drm/i915/intel_hotplug.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c index 875d5d218d5c..ab7e8dd0cf5b 100644 --- a/drivers/gpu/drm/i915/intel_hotplug.c +++ b/drivers/gpu/drm/i915/intel_hotplug.c @@ -245,7 +245,8 @@ static void intel_hpd_irq_storm_reenable_work(struct work_struct *work) drm_for_each_connector_iter(connector, &conn_iter) { struct intel_connector *intel_connector = to_intel_connector(connector);

- if (intel_connector->encoder->hpd_pin == i) { + if (intel_connector->encoder && + (intel_connector->encoder->hpd_pin == i)) { if (connector->polled != intel_connector->polled) DRM_DEBUG_DRIVER("Reenabling HPD on connector %s\n", connector->name); @@ -546,6 +547,7 @@ static void i915_hpd_poll_init_work(struct work_struct *work) continue;

if (!connector->polled && I915_HAS_HOTPLUG(dev_priv) && + intel_connector->encoder && intel_connector->encoder->hpd_pin > HPD_NONE) { connector->polled = enabled ? DRM_CONNECTOR_POLL_CONNECT |