[Intel-gfx] drm/i915 connector list locking issues..

[Linus Torvalds]

I didn't notice this until now, because my laptop still *works*, but
there seems to be a locking issue wth the drm connector list in the
i915 driver init path.

See appended call trace.

I don't know what part of the trace is supposed to get the mode_config
locks - maybe it's the generic drm kms helpers that are broken rather
than the i915 driver.

Is nobody else seeing this? This is on my bog-standard intel laptop
(Dell XPS13 as you can see in the warning). I haven't tried to see
when it started, but it didn't happen in 4.10-rc4. So it's recent.

If I had to guess, I'd blame commit 3846fd9b8600 ("drm/probe-helpers:
Drop locking from poll_enable"). Is it just that the check is now
wrong?

                Linus

---

  [drm] Found 64MB of eDRAM
  [drm] Memory usable by graphics device = 4096M
  checking generic (90000000 15f9000) vs hw (90000000 10000000)
  fb: switching to inteldrmfb from EFI VGA
  Console: switching to colour dummy device 80x25
  [drm] Replacing VGA console driver
  [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
  [drm] Driver supports precise vblank timestamp query.
  [drm] Finished loading i915/skl_dmc_ver1_26.bin (v1.26)
  i915 0000:00:02.0: vgaarb: changed VGA decodes:
olddecodes=io+mem,decodes=io+mem:owns=io+mem
  [drm] GuC firmware load skipped
  ------------[ cut here ]------------
  WARNING: CPU: 3 PID: 390 at ./include/drm/drm_crtc.h:857
drm_kms_helper_poll_enable.part.3+0xa8/0xc0 [drm_kms_helper]
  Modules linked in: rtsx_pci_sdmmc mmc_core crct10dif_pclmul
crc32_pclmul crc32c_intel i915(+) ghash_clmulni_intel serio_raw
i2c_algo_bit drm_kms_helper nvme rtsx_pci syscopyarea nvme_core
sysfillrect sysimgblt fb_sys_fops drm i2c_hid video fjes
  CPU: 3 PID: 390 Comm: systemd-udevd Not tainted
4.10.0-rc5-00071-ga4685d2f58e2 #10
  Hardware name: Dell Inc. XPS 13 9350/09JHRY, BIOS 1.4.12 11/30/2016
  Call Trace:
   drm_kms_helper_poll_enable.part.3+0xa8/0xc0 [drm_kms_helper]
   drm_kms_helper_poll_init+0x7e/0x90 [drm_kms_helper]
   i915_driver_load+0x13f0/0x1440 [i915]
   i915_pci_probe+0x4f/0x70 [i915]
   local_pci_probe+0x45/0xa0
   pci_device_probe+0x103/0x150
   driver_probe_device+0x2bb/0x460
   __driver_attach+0xdf/0xf0
   bus_for_each_dev+0x6c/0xc0
   driver_attach+0x1e/0x20
   bus_add_driver+0x170/0x270
   driver_register+0x60/0xe0
   __pci_register_driver+0x4c/0x50
   i915_init+0x57/0x5a [i915]
   do_one_initcall+0x52/0x1a0
   do_init_module+0x5f/0x1f8
   load_module+0x235f/0x2950
   SYSC_finit_module+0xdf/0x110
   SyS_finit_module+0xe/0x10
   do_syscall_64+0x61/0x170
   entry_SYSCALL64_slow_path+0x25/0x25
  RIP: 0033:0x7f772c536239
  RSP: 002b:00007ffe3b26a3f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
  RAX: ffffffffffffffda RBX: 0000561083f72f40 RCX: 00007f772c536239
  RDX: 0000000000000000 RSI: 00007f772cc3ea75 RDI: 0000000000000014
  RBP: 00007f772cc3ea75 R08: 0000000000000000 R09: 00007ffe3b26a510
  R10: 0000000000000014 R11: 0000000000000246 R12: 0000000000000000
  R13: 0000561083f751d0 R14: 0000000000020000 R15: 0000561082b23f4a
  ---[ end trace 311d7fe73771357e ]---
  usb 1-4: new full-speed USB device number 3 using xhci_hcd
  ACPI: Video Device [GFX0] (multi-head: yes  rom: no  post: no)
  input: Video Bus as
/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/LNXVIDEO:00/input/input7
  [drm] Initialized i915 1.6.0 20161121 for 0000:00:02.0 on minor 0