mbox series

[0/2] Stop users from using the device on driver unbind

Message ID 20190405130235.7707-1-janusz.krzysztofik@linux.intel.com (mailing list archive)
Headers show
Series Stop users from using the device on driver unbind | expand

Message

Janusz Krzysztofik April 5, 2019, 1:02 p.m. UTC 
Use drm_dev_unplug() to have device resources protected from user access
by DRM layer as soon as the driver is going to be unbound.  Also, cancel
all pending work so associated resources can be quickly released.

Janusz Krzysztofik (2):
  drm/i915: Use drm_dev_unplug()
  drm/i915: Mark GEM wedged right after marking device unplugged

 drivers/gpu/drm/i915/i915_drv.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

I'm resending these two patches together in series to make the robot
happy about the second one.  Also, I've added the Suggested-by: clause
to credit actual Chris' contribution.

Thanks,
Janusz

Comments

Chris Wilson April 5, 2019, 4:26 p.m. UTC | #1 
Quoting Patchwork (2019-04-05 17:20:39)
> == Series Details ==
> 
> Series: Stop users from using the device on driver unbind
> URL   : https://patchwork.freedesktop.org/series/59064/
> State : failure
> 
> == Summary ==
> 
> CI Bug Log - changes from CI_DRM_5881 -> Patchwork_12699
> ====================================================
> 
> Summary
> -------
> 
>   **FAILURE**
> 
>   Serious unknown changes coming with Patchwork_12699 absolutely need to be
>   verified manually.
>   
>   If you think the reported changes have nothing to do with the changes
>   introduced in Patchwork_12699, please notify your bug team to allow them
>   to document this new failure mode, which will reduce false positives in CI.
> 
>   External URL: https://patchwork.freedesktop.org/api/1.0/series/59064/revisions/1/mbox/
> 
> Possible new issues
> -------------------
> 
>   Here are the unknown changes that may have been introduced in Patchwork_12699:
> 
> ### IGT changes ###
> 
> #### Possible regressions ####
> 
>   * igt@i915_module_load@reload:

2 issues, it appears:

<4> [271.799080] WARN_ON(dev_priv->mm.object_count)
<4> [271.799241] WARNING: CPU: 0 PID: 3288 at drivers/gpu/drm/i915/i915_gem.c:5145 i915_gem_cleanup_early+0x104/0x110 [i915]
<4> [271.799249] Modules linked in: vgem snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic i915(-) mei_hdcp x86_pkg_temp_thermal btusb coretemp btrtl btbcm btintel bluetooth crct10dif_pclmul crc32_pclmul snd_hda_codec snd_hwdep ghash_clmulni_intel snd_hda_core e1000e ecdh_generic snd_pcm mei_me ptp prime_numbers pps_core mei [last unloaded: snd_hda_intel]
<4> [271.799302] CPU: 0 PID: 3288 Comm: i915_module_loa Tainted: G     U            5.1.0-rc3-CI-Patchwork_12699+ #1
<4> [271.799307] Hardware name:  /NUC6i7KYB, BIOS KYSKLi70.86A.0059.2018.1122.1431 11/22/2018
<4> [271.799406] RIP: 0010:i915_gem_cleanup_early+0x104/0x110 [i915]
<4> [271.799412] Code: 00 00 48 c7 c2 d0 6b 3d a0 48 c7 c7 ca 5c 2c a0 e8 c1 b5 ec e0 0f 0b 48 c7 c6 68 c0 3f a0 48 c7 c7 63 88 42 a0 e8 9c 77 de e0 <0f> 0b e9 40 ff ff ff 0f 1f 44 00 00 e8 5b 7e 00 00 31 c0 c3 0f 1f
<4> [271.799417] RSP: 0018:ffffc90000453dd0 EFLAGS: 00010282
<4> [271.799423] RAX: 0000000000000000 RBX: ffff88849afd0000 RCX: 0000000000000000
<4> [271.799428] RDX: 0000000000000006 RSI: ffff88849ee130b8 RDI: ffffffff8211dc4d
<4> [271.799432] RBP: ffff88849afd7630 R08: 00000000028bc995 R09: 0000000000000000
<4> [271.799436] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffffa04a81e0
<4> [271.799440] R13: 0000000000000000 R14: 0000000000000000 R15: ffffffffa04a82d0
<4> [271.799446] FS:  00007f31e8cec980(0000) GS:ffff8884aee00000(0000) knlGS:0000000000000000
<4> [271.799451] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4> [271.799455] CR2: 00007ffea58773d8 CR3: 000000044cfc6003 CR4: 00000000003606f0
<4> [271.799459] Call Trace:
<4> [271.799531]  i915_driver_cleanup_early+0x30/0x70 [i915]
<4> [271.799603]  i915_driver_release+0xa/0x30 [i915]
<4> [271.799672]  i915_driver_unload+0x6a/0x120 [i915]
<4> [271.799748]  i915_pci_remove+0x19/0x30 [i915]
<4> [271.799765]  pci_device_remove+0x36/0xb0

we leaked objects (don't recall that in recent times)

and

<4> [271.812054] general protection fault: 0000 [#1] PREEMPT SMP PTI
<4> [271.812079] CPU: 3 PID: 3288 Comm: i915_module_loa Tainted: G     U  W         5.1.0-rc3-CI-Patchwork_12699+ #1
<4> [271.812094] Hardware name:  /NUC6i7KYB, BIOS KYSKLi70.86A.0059.2018.1122.1431 11/22/2018
<4> [271.812172] RIP: 0010:intel_uncore_forcewake_get+0x0/0xa0 [i915]
<4> [271.812183] Code: e8 fd ff ff 66 0f 1f 44 00 00 48 83 c7 60 e9 17 e0 d9 e0 0f 1f 80 00 00 00 00 e9 5b ed f6 ff 90 66 2e 0f 1f 84 00 00 00 00 00 <48> 83 7f 78 00 74 49 41 55 41 54 55 53 89 f5 4c 8b 67 08 48 89 fb
<4> [271.812208] RSP: 0018:ffffc90000453d78 EFLAGS: 00010282
<4> [271.812217] RAX: 6b6b6b6b6b6b6b6b RBX: ffff88849afd75f0 RCX: 0000000000000000
<4> [271.812228] RDX: 0000000000000001 RSI: 00000000000001ff RDI: 6b6b6b6b6b6b7a1b
<4> [271.812239] RBP: ffff888498992158 R08: 000000000029049a R09: ffff8884ac8af000
<4> [271.812249] R10: ffff8884ac8afc40 R11: ffff8884ad266f98 R12: ffff88849afd7630
<4> [271.812260] R13: ffff88849afd0000 R14: 0000000000000000 R15: ffffffffa04a82d0
<4> [271.812271] FS:  00007f31e8cec980(0000) GS:ffff8884aeec0000(0000) knlGS:0000000000000000
<4> [271.812283] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4> [271.812292] CR2: 000055f1c5db3128 CR3: 000000044cfc6004 CR4: 00000000003606e0
<4> [271.812303] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
<4> [271.812314] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
<4> [271.812324] Call Trace:
<4> [271.812367]  reset_prepare+0x34/0x60 [i915]
<4> [271.812411]  __i915_gem_set_wedged.part.4+0x55/0x190 [i915]
<4> [271.812425]  ? _raw_spin_unlock_irqrestore+0x39/0x60
<4> [271.812469]  i915_gem_set_wedged+0x56/0x60 [i915]
<4> [271.812511]  i915_driver_unload+0x72/0x120 [i915]
<4> [271.812553]  i915_pci_remove+0x19/0x30 [i915]
<4> [271.812565]  pci_device_remove+0x36/0xb0
<4> [271.812574]  device_release_driver_internal+0xdf/0x1d0
<4> [271.812584]  driver_detach+0x3e/0x80
<4> [271.812593]  bus_remove_driver+0x53/0xd0
<4> [271.812602]  pci_unregister_driver+0x25/0xa0
<4> [271.812669]  i915_exit+0x16/0x1c [i915]

where we try to wedge but the device is full of poison 0x6b. We are not
even in the fault-injection test, so that device should be after a
successful load.

Hmm, certainly didn't expect the latter. 
-Chris
Chris Wilson April 5, 2019, 5:37 p.m. UTC | #2 
Quoting Chris Wilson (2019-04-05 17:26:46)
> Quoting Patchwork (2019-04-05 17:20:39)
> > == Series Details ==
> > 
> > Series: Stop users from using the device on driver unbind
> > URL   : https://patchwork.freedesktop.org/series/59064/
> > State : failure
> > 
> > == Summary ==
> > 
> > CI Bug Log - changes from CI_DRM_5881 -> Patchwork_12699
> > ====================================================
> > 
> > Summary
> > -------
> > 
> >   **FAILURE**
> > 
> >   Serious unknown changes coming with Patchwork_12699 absolutely need to be
> >   verified manually.
> >   
> >   If you think the reported changes have nothing to do with the changes
> >   introduced in Patchwork_12699, please notify your bug team to allow them
> >   to document this new failure mode, which will reduce false positives in CI.
> > 
> >   External URL: https://patchwork.freedesktop.org/api/1.0/series/59064/revisions/1/mbox/
> > 
> > Possible new issues
> > -------------------
> > 
> >   Here are the unknown changes that may have been introduced in Patchwork_12699:
> > 
> > ### IGT changes ###
> > 
> > #### Possible regressions ####
> > 
> >   * igt@i915_module_load@reload:
> 
> 2 issues, it appears:
> 
> <4> [271.799080] WARN_ON(dev_priv->mm.object_count)
> <4> [271.799241] WARNING: CPU: 0 PID: 3288 at drivers/gpu/drm/i915/i915_gem.c:5145 i915_gem_cleanup_early+0x104/0x110 [i915]
> <4> [271.799249] Modules linked in: vgem snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic i915(-) mei_hdcp x86_pkg_temp_thermal btusb coretemp btrtl btbcm btintel bluetooth crct10dif_pclmul crc32_pclmul snd_hda_codec snd_hwdep ghash_clmulni_intel snd_hda_core e1000e ecdh_generic snd_pcm mei_me ptp prime_numbers pps_core mei [last unloaded: snd_hda_intel]
> <4> [271.799302] CPU: 0 PID: 3288 Comm: i915_module_loa Tainted: G     U            5.1.0-rc3-CI-Patchwork_12699+ #1
> <4> [271.799307] Hardware name:  /NUC6i7KYB, BIOS KYSKLi70.86A.0059.2018.1122.1431 11/22/2018
> <4> [271.799406] RIP: 0010:i915_gem_cleanup_early+0x104/0x110 [i915]
> <4> [271.799412] Code: 00 00 48 c7 c2 d0 6b 3d a0 48 c7 c7 ca 5c 2c a0 e8 c1 b5 ec e0 0f 0b 48 c7 c6 68 c0 3f a0 48 c7 c7 63 88 42 a0 e8 9c 77 de e0 <0f> 0b e9 40 ff ff ff 0f 1f 44 00 00 e8 5b 7e 00 00 31 c0 c3 0f 1f
> <4> [271.799417] RSP: 0018:ffffc90000453dd0 EFLAGS: 00010282
> <4> [271.799423] RAX: 0000000000000000 RBX: ffff88849afd0000 RCX: 0000000000000000
> <4> [271.799428] RDX: 0000000000000006 RSI: ffff88849ee130b8 RDI: ffffffff8211dc4d
> <4> [271.799432] RBP: ffff88849afd7630 R08: 00000000028bc995 R09: 0000000000000000
> <4> [271.799436] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffffa04a81e0
> <4> [271.799440] R13: 0000000000000000 R14: 0000000000000000 R15: ffffffffa04a82d0
> <4> [271.799446] FS:  00007f31e8cec980(0000) GS:ffff8884aee00000(0000) knlGS:0000000000000000
> <4> [271.799451] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4> [271.799455] CR2: 00007ffea58773d8 CR3: 000000044cfc6003 CR4: 00000000003606f0
> <4> [271.799459] Call Trace:
> <4> [271.799531]  i915_driver_cleanup_early+0x30/0x70 [i915]
> <4> [271.799603]  i915_driver_release+0xa/0x30 [i915]
> <4> [271.799672]  i915_driver_unload+0x6a/0x120 [i915]
> <4> [271.799748]  i915_pci_remove+0x19/0x30 [i915]
> <4> [271.799765]  pci_device_remove+0x36/0xb0

So this is the bizarre part. We end up in the final i915_driver_release
because it appears that drm_dev_unplug() drops a reference. I couldn't
see where...

[   24.960676] WARNING: CPU: 2 PID: 637 at drivers/gpu/drm/drm_drv.c:895 drm_dev_put+0x8/0x60
[   24.960735] Modules linked in: nls_ascii nls_cp437 vfat fat crct10dif_pclmul crc32_pclmul crc32c_intel i915(-) aesni_intel aes_x86_64 crypto_simd cryptd glue_helper intel_cstate intel_uncore intel_rapl_perf efivars i2c_i801 intel_gtt drm_kms_helper ahci libahci video button efivarfs
[   24.960848] CPU: 2 PID: 637 Comm: i915_module_loa Tainted: G    BU            5.1.0-rc3+ #526
[   24.960897] Hardware name: Intel Corporation NUC7i5BNK/NUC7i5BNB, BIOS BNKBL357.86A.0052.2017.0918.1346 09/18/2017
[   24.960952] RIP: 0010:drm_dev_put+0x8/0x60
[   24.960993] Code: 48 8d 7b 60 e8 d9 8b c7 ff 48 8b 7b 60 5b 5d e9 0e 4f c7 ff 48 89 df e8 06 c2 ff ff e9 3f ff ff ff 90 48 85 ff 75 01 c3 55 53 <0f> 0b f0 ff 4f 14 0f 88 64 b7 2d 00 74 03 5b 5d c3 48 89 fb 48 8d
[   24.961066] RSP: 0018:ffff88872587fc80 EFLAGS: 00010286
[   24.961107] RAX: 0000000000000000 RBX: ffff88873f020000 RCX: ffffffff81680444
[   24.961151] RDX: dffffc0000000000 RSI: dffffc0000000000 RDI: ffff88873f020000
[   24.961195] RBP: ffff88873f02ad88 R08: 0000000000000000 R09: fffffbfff04824c5
[   24.961240] R10: fffffbfff04824c5 R11: ffffffff8241262b R12: ffff88881ab067a0
[   24.961284] R13: ffffffffa0618c00 R14: ffff88881ab06660 R15: ffff88881ab06960
[   24.961330] FS:  00007fdba43279c0(0000) GS:ffff88881f500000(0000) knlGS:0000000000000000
[   24.961377] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   24.961618] CR2: 00007fffc0229f80 CR3: 0000000726506001 CR4: 00000000001606e0
[   24.961662] Call Trace:
[   24.961773]  i915_driver_unload+0x72/0x130 [i915]
[   24.961888]  i915_pci_remove+0x2a/0x50 [i915]
[   24.961929]  pci_device_remove+0xaa/0x180
[   24.961968]  ? pcibios_free_irq+0x10/0x10
[   24.962005]  ? up_read+0xc2/0xe0
[   24.962041]  device_release_driver_internal+0x12b/0x260
[   24.962081]  driver_detach+0x6f/0xca
[   24.962117]  bus_remove_driver+0xc4/0x141
[   24.962157]  pci_unregister_driver+0x32/0xf0
[   24.962274]  i915_exit+0x16/0x1c [i915]
[   24.962312]  __x64_sys_delete_module+0x20e/0x2b0
[   24.962351]  ? __ia32_sys_delete_module+0x2b0/0x2b0
[   24.962390]  ? lockdep_hardirqs_on+0x11/0x250
[   24.962428]  ? lockdep_hardirqs_off+0x1a/0x100
[   24.962465]  ? trace_hardirqs_off_thunk+0x1a/0x1c
[   24.962504]  do_syscall_64+0x5d/0x200
[   24.962542]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   24.962581] RIP: 0033:0x7fdba6189137

which gdb insists is the drm_dev_unplug() call. Oh drm-tip, not dinq.
Noralf has been playing.

We have

commit ba3bf37e150a99b51b13f5cebf89715685d21212
Author: Noralf Trønnes <noralf@tronnes.org>
Date:   Fri Feb 8 15:01:03 2019 +0100

    drm/drv: drm_dev_unplug(): Move out drm_dev_put() call

    This makes it possible to use drm_dev_unplug() with the upcoming
    devm_drm_dev_init() which will do drm_dev_put() in its release callback.

but drm-tip has a mismash of trees and a conflict that brings the
drm_dev_put() here right back in.
-Chris
Janusz Krzysztofik April 8, 2019, 8:19 a.m. UTC | #3 
On Friday, April 5, 2019 7:37:04 PM CEST Chris Wilson wrote:
> Quoting Chris Wilson (2019-04-05 17:26:46)
> 
> > Quoting Patchwork (2019-04-05 17:20:39)
> > 
> > > == Series Details ==
> > > 
> > > Series: Stop users from using the device on driver unbind
> > > URL   : https://patchwork.freedesktop.org/series/59064/
> > > State : failure
> > > 
> > > == Summary ==
> > > 
> > > CI Bug Log - changes from CI_DRM_5881 -> Patchwork_12699
> > > ====================================================
> > > 
> > > Summary
> > > -------
> > > 
> > >   **FAILURE**
> > >   
> > >   Serious unknown changes coming with Patchwork_12699 absolutely need to
> > >   be
> > >   verified manually.
> > >   
> > >   If you think the reported changes have nothing to do with the changes
> > >   introduced in Patchwork_12699, please notify your bug team to allow
> > >   them
> > >   to document this new failure mode, which will reduce false positives
> > >   in CI.
> > >   
> > >   External URL:
> > >   https://patchwork.freedesktop.org/api/1.0/series/59064/revisions/1/mb
> > >   ox/> > 
> > > Possible new issues
> > > -------------------
> > > 
> > >   Here are the unknown changes that may have been introduced in 
Patchwork_12699:
> > > ### IGT changes ###
> > > 
> > > #### Possible regressions ####
> > > 
> > >   * igt@i915_module_load@reload:
> > 2 issues, it appears:
> > 
> > <4> [271.799080] WARN_ON(dev_priv->mm.object_count)
> > <4> [271.799241] WARNING: CPU: 0 PID: 3288 at
> > drivers/gpu/drm/i915/i915_gem.c:5145 i915_gem_cleanup_early+0x104/0x110
> > [i915] <4> [271.799249] Modules linked in: vgem snd_hda_codec_hdmi
> > snd_hda_codec_realtek snd_hda_codec_generic i915(-) mei_hdcp
> > x86_pkg_temp_thermal btusb coretemp btrtl btbcm btintel bluetooth
> > crct10dif_pclmul crc32_pclmul snd_hda_codec snd_hwdep ghash_clmulni_intel
> > snd_hda_core e1000e ecdh_generic snd_pcm mei_me ptp prime_numbers
> > pps_core mei [last unloaded: snd_hda_intel] <4> [271.799302] CPU: 0 PID:
> > 3288 Comm: i915_module_loa Tainted: G     U           
> > 5.1.0-rc3-CI-Patchwork_12699+ #1 <4> [271.799307] Hardware name: 
> > /NUC6i7KYB, BIOS KYSKLi70.86A.0059.2018.1122.1431 11/22/2018 <4>
> > [271.799406] RIP: 0010:i915_gem_cleanup_early+0x104/0x110 [i915] <4>
> > [271.799412] Code: 00 00 48 c7 c2 d0 6b 3d a0 48 c7 c7 ca 5c 2c a0 e8 c1
> > b5 ec e0 0f 0b 48 c7 c6 68 c0 3f a0 48 c7 c7 63 88 42 a0 e8 9c 77 de e0
> > <0f> 0b e9 40 ff ff ff 0f 1f 44 00 00 e8 5b 7e 00 00 31 c0 c3 0f 1f <4>
> > [271.799417] RSP: 0018:ffffc90000453dd0 EFLAGS: 00010282
> > <4> [271.799423] RAX: 0000000000000000 RBX: ffff88849afd0000 RCX:
> > 0000000000000000 <4> [271.799428] RDX: 0000000000000006 RSI:
> > ffff88849ee130b8 RDI: ffffffff8211dc4d <4> [271.799432] RBP:
> > ffff88849afd7630 R08: 00000000028bc995 R09: 0000000000000000 <4>
> > [271.799436] R10: 0000000000000000 R11: 0000000000000000 R12:
> > ffffffffa04a81e0 <4> [271.799440] R13: 0000000000000000 R14:
> > 0000000000000000 R15: ffffffffa04a82d0 <4> [271.799446] FS: 
> > 00007f31e8cec980(0000) GS:ffff8884aee00000(0000) knlGS:0000000000000000
> > <4> [271.799451] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 <4>
> > [271.799455] CR2: 00007ffea58773d8 CR3: 000000044cfc6003 CR4:
> > 00000000003606f0 <4> [271.799459] Call Trace:
> > <4> [271.799531]  i915_driver_cleanup_early+0x30/0x70 [i915]
> > <4> [271.799603]  i915_driver_release+0xa/0x30 [i915]
> > <4> [271.799672]  i915_driver_unload+0x6a/0x120 [i915]
> > <4> [271.799748]  i915_pci_remove+0x19/0x30 [i915]
> > <4> [271.799765]  pci_device_remove+0x36/0xb0
> 
> So this is the bizarre part. We end up in the final i915_driver_release
> because it appears that drm_dev_unplug() drops a reference. I couldn't
> see where...
> 
> [   24.960676] WARNING: CPU: 2 PID: 637 at drivers/gpu/drm/drm_drv.c:895
> drm_dev_put+0x8/0x60 [   24.960735] Modules linked in: nls_ascii nls_cp437
> vfat fat crct10dif_pclmul crc32_pclmul crc32c_intel i915(-) aesni_intel
> aes_x86_64 crypto_simd cryptd glue_helper intel_cstate intel_uncore
> intel_rapl_perf efivars i2c_i801 intel_gtt drm_kms_helper ahci libahci
> video button efivarfs [   24.960848] CPU: 2 PID: 637 Comm: i915_module_loa
> Tainted: G    BU            5.1.0-rc3+ #526 [   24.960897] Hardware name:
> Intel Corporation NUC7i5BNK/NUC7i5BNB, BIOS
> BNKBL357.86A.0052.2017.0918.1346 09/18/2017 [   24.960952] RIP:
> 0010:drm_dev_put+0x8/0x60
> [   24.960993] Code: 48 8d 7b 60 e8 d9 8b c7 ff 48 8b 7b 60 5b 5d e9 0e 4f
> c7 ff 48 89 df e8 06 c2 ff ff e9 3f ff ff ff 90 48 85 ff 75 01 c3 55 53
> <0f> 0b f0 ff 4f 14 0f 88 64 b7 2d 00 74 03 5b 5d c3 48 89 fb 48 8d [  
> 24.961066] RSP: 0018:ffff88872587fc80 EFLAGS: 00010286
> [   24.961107] RAX: 0000000000000000 RBX: ffff88873f020000 RCX:
> ffffffff81680444 [   24.961151] RDX: dffffc0000000000 RSI: dffffc0000000000
> RDI: ffff88873f020000 [   24.961195] RBP: ffff88873f02ad88 R08:
> 0000000000000000 R09: fffffbfff04824c5 [   24.961240] R10: fffffbfff04824c5
> R11: ffffffff8241262b R12: ffff88881ab067a0 [   24.961284] R13:
> ffffffffa0618c00 R14: ffff88881ab06660 R15: ffff88881ab06960 [   24.961330]
> FS:  00007fdba43279c0(0000) GS:ffff88881f500000(0000)
> knlGS:0000000000000000 [   24.961377] CS:  0010 DS: 0000 ES: 0000 CR0:
> 0000000080050033
> [   24.961618] CR2: 00007fffc0229f80 CR3: 0000000726506001 CR4:
> 00000000001606e0 [   24.961662] Call Trace:
> [   24.961773]  i915_driver_unload+0x72/0x130 [i915]
> [   24.961888]  i915_pci_remove+0x2a/0x50 [i915]
> [   24.961929]  pci_device_remove+0xaa/0x180
> [   24.961968]  ? pcibios_free_irq+0x10/0x10
> [   24.962005]  ? up_read+0xc2/0xe0
> [   24.962041]  device_release_driver_internal+0x12b/0x260
> [   24.962081]  driver_detach+0x6f/0xca
> [   24.962117]  bus_remove_driver+0xc4/0x141
> [   24.962157]  pci_unregister_driver+0x32/0xf0
> [   24.962274]  i915_exit+0x16/0x1c [i915]
> [   24.962312]  __x64_sys_delete_module+0x20e/0x2b0
> [   24.962351]  ? __ia32_sys_delete_module+0x2b0/0x2b0
> [   24.962390]  ? lockdep_hardirqs_on+0x11/0x250
> [   24.962428]  ? lockdep_hardirqs_off+0x1a/0x100
> [   24.962465]  ? trace_hardirqs_off_thunk+0x1a/0x1c
> [   24.962504]  do_syscall_64+0x5d/0x200
> [   24.962542]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [   24.962581] RIP: 0033:0x7fdba6189137
> 
> which gdb insists is the drm_dev_unplug() call. Oh drm-tip, not dinq.
> Noralf has been playing.
> 
> We have
> 
> commit ba3bf37e150a99b51b13f5cebf89715685d21212
> Author: Noralf Trønnes <noralf@tronnes.org>
> Date:   Fri Feb 8 15:01:03 2019 +0100
> 
>     drm/drv: drm_dev_unplug(): Move out drm_dev_put() call
> 
>     This makes it possible to use drm_dev_unplug() with the upcoming
>     devm_drm_dev_init() which will do drm_dev_put() in its release callback.
> 
> but drm-tip has a mismash of trees and a conflict that brings the
> drm_dev_put() here right back in.

Yeah, I can see the "drm: Fix drm_release() and device unplug" patch,
which is patch 1/2 of the series that introduced commit ba3bf37e150a
("drm/drv: drm_dev_unplug(): Move out drm_dev_put() call"), is applied
twice in drm-tip, one instance coming from drm-fixes as
commit 3f04e0a6cfeb, the other from drm-next as 1ee57d4d75fb.

(there were two).  Playing with it, I learned by excercise it was
certainly too early for us to drop the reference at that point.  I took
the opportunity that drm_dev_put() was finally moved out of
drm_dev_unplug() so we could use it in place of drm_dev_unregister().  

Janusz

> -Chris