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

[Daniel Vetter]

On Mon, Jan 9, 2017 at 2:40 PM, Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
> Well, now I found where the -2 comes from.
> intel_dp_register_mst_connector() calls drm_connector_register(), which
> fails to add the kobject (warning below).  But, it does zero error
> checking on the drm_connector_register() call and leaves the
> partially-constructed connector in place.
>
> The next time some poor, hapless code goes and tries to do anything with
> that kdev, they oops.  I'm perplexed by this, though.  The
> drm_dp_mst_topology_cbs->register_connector just returns void.  It seems
> a bit goofy that it can't even _return_ failure.
>
> Is there some stable code to go back to here?  Or, is there something
> about my configuration that's unique?  I really wonder why nobody else
> is running into this.
>
> There's probably some other race going on here.  This warning doesn't
> happen on every boot.

This smells more like the root-cause: Something goes wrong on boot
that prevents connectors from properly registering, then we fall over
later on. And the register callback is intentionally void, assuming
that any prep work has been done earlier and that therefore the
register step can't fail. Can you pls check whether the oops later on
only happens together with this warning at boot, or whether they're
not correlated?

Still no idea though why this blows up for you.
-Daniel

>
>> [    1.396475] ------------[ cut here ]------------
>> [    1.396486] WARNING: CPU: 0 PID: 91 at lib/kobject.c:244 kobject_add_internal+0x108/0x2d0
>> [    1.396492] kobject_add_internal failed for card0-DP-3 (error: -2 parent: card0)
>> [    1.396496] Modules linked in:
>> [    1.396500] CPU: 0 PID: 91 Comm: kworker/0:2 Not tainted 4.10.0-rc2-dirty #58
>> [    1.396503] Hardware name: LENOVO 20F5S7V800/20F5S7V800, BIOS R02ET50W (1.23 ) 09/20/2016
>> [    1.396509] Workqueue: events_long drm_dp_mst_link_probe_work
>> [    1.396511] Call Trace:
>> [    1.396517]  dump_stack+0x67/0x99
>> [    1.396521]  __warn+0xd1/0xf0
>> [    1.396524]  warn_slowpath_fmt+0x4f/0x60
>> [    1.396527]  kobject_add_internal+0x108/0x2d0
>> [    1.396531]  ? vsnprintf+0x112/0x4b0
>> [    1.396533]  kobject_add+0x65/0xb0
>> [    1.396537]  ? klist_init+0x31/0x40
>> [    1.396542]  device_add+0x102/0x5d0
>> [    1.396546]  ? kfree_const+0x22/0x30
>> [    1.396549]  device_create_groups_vargs+0xd8/0x100
>> [    1.396553]  device_create_with_groups+0x36/0x40
>> [    1.396557]  ? drm_fb_helper_add_one_connector+0x57/0xd0
>> [    1.396561]  ? kmem_cache_alloc_trace+0x1d2/0x1f0
>> [    1.396566]  drm_sysfs_connector_add+0x60/0xe0
>> [    1.396570]  drm_connector_register+0x21/0xc0
>> [    1.396575]  intel_dp_register_mst_connector+0x41/0x50
>> [    1.396579]  drm_dp_add_port+0x350/0x450
>> [    1.396583]  ? rcu_early_boot_tests+0x1/0x10
>> [    1.396587]  ? schedule_timeout+0x1cd/0x390
>> [    1.396591]  ? __might_sleep+0x4a/0x90
>> [    1.396594]  ? mutex_lock+0x25/0x50
>> [    1.396597]  ? drm_dp_mst_wait_tx_reply+0x118/0x1e0
>> [    1.396600]  ? prepare_to_wait_event+0x120/0x120
>> [    1.396603]  ? drm_dp_check_mstb_guid+0x3d/0x120
>> [    1.396606] drm_sysfs_connector_add() connector: ffff88040ed3f000 kdev: ffff88040c55dc00
>> [    1.396610]  drm_dp_send_link_address+0x185/0x1f0
>> [    1.396614]  drm_dp_check_and_send_link_address+0xad/0xc0
>> [    1.396617]  drm_dp_mst_link_probe_work+0x57/0xa0
>> [    1.396620]  process_one_work+0x14b/0x430
>> [    1.396623]  worker_thread+0x12b/0x4a0
>> [    1.396626]  kthread+0x10c/0x140
>> [    1.396629]  ? process_one_work+0x430/0x430
>> [    1.396632]  ? kthread_create_on_node+0x40/0x40
>> [    1.396635]  ret_from_fork+0x27/0x40
>> [    1.396639] ---[ end trace dd05bb2cd9ebd900 ]---
>> [    1.396643] drm_sysfs_connector_add() connector: ffff88040c75a000 kdev: fffffffffffffffe
>> [    1.396648] [drm:drm_sysfs_connector_add] *ERROR* failed to register connector device: -2
>> [    1.396651] drm_connector_register(ffff88040ed3f000) connector->registered: 1
>> [    1.396666] drm_sysfs_connector_add() connector: ffff88040ed3f800 kdev: ffff88040c55e400
>> [    1.396700] drm_connector_register(ffff88040ed3f800) connector->registered: 1
>> [    1.396717] drm_sysfs_connector_add() connector: ffff88040ed39800 kdev: ffff88040c55e800
>> [    1.396726] drm_connector_register(ffff88040ed39800) connector->registered: 1
>> [    1.396743] drm_sysfs_connector_add() connector: ffff88040c758000 kdev: ffff88040c55ec00
>> [    1.396769] drm_connector_register(ffff88040c758000) connector->registered: 1
>> [    1.396786] drm_sysfs_connector_add() connector: ffff88040c758800 kdev: ffff88040c55f000
>> [    1.396799] drm_connector_register(ffff88040c758800) connector->registered: 1
>> [    1.396804] drm_connector_register(ffff88040c75a000) connector->registered: 1
>> [    1.398665] ACPI: Video Device [GFX0] (multi-head: yes  rom: no  post: no)
>> [    1.398893] drm_sysfs_connector_add() connector: ffff88040c75b000 kdev: ffff88040c790400
>> [    1.398907] drm_connector_register(ffff88040c75b000) connector->registered: 1
>> [    1.398930] drm_sysfs_connector_add() connector: ffff88040c75c000 kdev: ffff88040c790800
>> [    1.398939] drm_connector_register(ffff88040c75c000) connector->registered: 1
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch