Re: [Intel-gfx] 4.10-rc2 oops in DRM connector code

[Dave Hansen <dave.hansen@intel.com>]

On 01/09/2017 02:15 AM, Daniel Vetter wrote:
...
> Can you pls do some printk tracing to make sure that without your patch
> we're indeed releasing the same connector twice from this loop? I suspect
> you're just ever-so-slightly shifting the timing and things blow up
> somewhre else. But no idea where :(

Your suspicious appear correct.  I still get an oops even with my patch
applied.  I did add some printk's but they're weird.  I'm seeing a
'kdev' that looks to be -2, although it should never get set to that
unless device_create_with_groups() and th error checking failed somehow.

I'll take out the locking portion of the patch and add some more
printk's and see if anything else shows up.  Here's a copy of the
printk's and associated oops, with my locking modification patch
applied, if this helps at all:

> [ 7927.049763] drm_dp_destroy_port() kfree(ffff88040c759000)
> [ 7927.050039] drm_dp_destroy_connector_work() port: ffff88040c759800 connector: ffff88040c75a000
> [ 7927.050061] drm_sysfs_connector_remove() connector: ffff88040c75a000 kdev: fffffffffffffffe
> [ 7927.050106] BUG: unable to handle kernel NULL pointer dereference at 000000000000009e
> [ 7927.050242] IP: device_del+0x19/0x330
> [ 7927.050300] PGD 0 
> [ 7927.050302] 
> [ 7927.050364] Oops: 0000 [#1] SMP
> [ 7927.050414] Modules linked in: netconsole ctr ccm ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 xt_CHECKSUM iptable_mangle xt_tcpudp bridge stp llc iptable_filter ip_tables ebtable_nat ebtables x_tables cmac rfcomm bnep dm_crypt arc4 iwlmvm mac80211 snd_hda_codec_hdmi iwlwifi snd_hda_codec_realtek snd_hda_codec_generic snd_hda_intel snd_seq_midi snd_seq_midi_event snd_hda_codec cfg80211 snd_hwdep snd_rawmidi intel_rapl snd_hda_core iosf_mbi snd_pcm snd_seq btusb x86_pkg_temp_thermal hid_logitech_hidpp btrtl btbcm btintel coretemp shpchp snd_timer ghash_clmulni_intel bluetooth joydev thinkpad_acpi snd_seq_device nvram wmi snd soundcore mac_hid aesni_intel aes_x86_64 crypto_simd cryptd glue_helper
> [ 7927.051492]  kvm_intel kvm irqbypass hid_generic hid_logitech_dj usbhid hid [last unloaded: netconsole]
> [ 7927.051642] CPU: 2 PID: 123 Comm: kworker/2:2 Tainted: G        W       4.10.0-rc2-dirty #53
> [ 7927.051763] Hardware name: LENOVO 20F5S7V800/20F5S7V800, BIOS R02ET50W (1.23 ) 09/20/2016
> [ 7927.051887] Workqueue: events drm_dp_destroy_connector_work
> [ 7927.051971] task: ffff88040c21bc00 task.stack: ffffc90002484000
> [ 7927.052065] RIP: 0010:device_del+0x19/0x330
> [ 7927.052129] RSP: 0018:ffffc90002487d58 EFLAGS: 00010282
> [ 7927.052209] RAX: 0000000000000000 RBX: fffffffffffffffe RCX: ffff88040c72d1f8
> [ 7927.052310] RDX: ffffffff81cb69b2 RSI: 0000000000000001 RDI: fffffffffffffffe
> [ 7927.052412] RBP: ffffc90002487d90 R08: 0000000000000000 R09: 0000000000000392
> [ 7927.052517] R10: 00000003e05de802 R11: 0000000000000000 R12: fffffffffffffffe
> [ 7927.052677] R13: ffff88040c516c18 R14: 0000000000000000 R15: ffff88040c516bd8
> [ 7927.052781] FS:  0000000000000000(0000) GS:ffff880421500000(0000) knlGS:0000000000000000
> [ 7927.052897] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 7927.052981] CR2: 000000000000009e CR3: 0000000001e0b000 CR4: 00000000003406e0
> [ 7927.053082] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 7927.053186] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [ 7927.053288] Call Trace:
> [ 7927.053338]  ? printk+0x4d/0x4f
> [ 7927.053396]  device_unregister+0x12/0x30
> [ 7927.053464]  drm_sysfs_connector_remove+0x57/0x70
> [ 7927.053538]  drm_connector_unregister.part.8+0x27/0x40
> [ 7927.053616]  drm_connector_unregister+0x14/0x20
> [ 7927.053690]  intel_dp_destroy_mst_connector+0x1a/0x80
> [ 7927.053771]  drm_dp_destroy_connector_work+0xce/0x150
> [ 7927.053850]  process_one_work+0x14b/0x430
> [ 7927.053914]  worker_thread+0x12b/0x4a0
> [ 7927.053982]  kthread+0x10c/0x140
> [ 7927.054037]  ? process_one_work+0x430/0x430
> [ 7927.054104]  ? kthread_create_on_node+0x40/0x40
> [ 7927.054179]  ret_from_fork+0x27/0x40
> [ 7927.054237] Code: 00 00 00 00 00 00 00 5b 41 5c 41 5d 5d c3 0f 1f 40 00 0f 1f 44 00 00 55 48 89 e5 41 57 41 56 41 55 41 54 49 89 fc 53 48 83 ec 10 <48> 8b 87 a0 00 00 00 4c 8b 2f 48 85 c0 74 1b 48 8b b8 90 00 00 
> [ 7927.054462] RIP: device_del+0x19/0x330 RSP: ffffc90002487d58
> [ 7927.054486] CR2: 000000000000009e
> [ 7927.065278] ---[ end trace 1a2a5ca2cf6c3a4f ]---