Re: [PATCH] drm: Don't race connector registration

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

I added some printk()s all over and gathered a bit more information
about what's going on.  It looks like the display doesn't work until the
drm connector code cleans up the *old* connector.  For some reason, it
isn't motivated to do that until I go to the console and back.

In this case, the display was connected to DP-4.
intel_dp_destroy_mst_connector() got called on it when I switched away,
but drm_connector_cleanup() did not get called.  Upon switching back
DP-3/5/6 get created.  One of these *eventually* ends up being
"enabled", but is not now.  When I switch over to the console,
drm_connector_cleanup() finally gets called on the old connector: DP-4
and I can switch back to X and I see one of DP-3/5/6 enabled and working.

Here are some snippets of dmesg interspersed with what I was doing:

Push DVI switch button to switch to other system:

> [ 6824.562838] drm_dp_destroy_port() kfree(ffff8801ade46800)
> [ 6824.563164] drm_dp_destroy_connector_work() port: ffff8801ade42000 connector: ffff8801ade46000
> [ 6824.563178] intel_dp_destroy_mst_connector() connector: ffff8801ade46000 name: DP-3 &name: ffff8801ade46048 intel_connector: ffff8801ade46000
> [ 6824.563186] drm_sysfs_connector_remove() connector: ffff8801ade46000 kdev: ffff8801a941b400
> [ 6824.571556] drm_connector_cleanup(ffff8801ade46000)::329 connector->registered: 0 cpu: 3
> [ 6824.571570] drm_connector_cleanup() kfree() connector->name: 'DP-3' &name: ffff8801ade46048
> [ 6824.571581] drm_dp_free_mst_port() kfree port: ffff8801ade42000
> [ 6824.571587] drm_dp_destroy_connector_work() port: ffff8801ade42800 connector: ffff8801ade47000
> [ 6824.571594] intel_dp_destroy_mst_connector() connector: ffff8801ade47000 name: DP-4 &name: ffff8801ade47048 intel_connector: ffff8801ade47000
> [ 6824.571601] drm_sysfs_connector_remove() connector: ffff8801ade47000 kdev: ffff8801a941a000
> [ 6824.571915] drm_dp_free_mst_port() kfree port: ffff8801ade42800
> [ 6824.571925] drm_dp_destroy_connector_work() port: ffff8801ade40800 connector: ffff8801ade43000
> [ 6824.571934] intel_dp_destroy_mst_connector() connector: ffff8801ade43000 name: DP-6 &name: ffff8801ade43048 intel_connector: ffff8801ade43000
> [ 6824.571943] drm_sysfs_connector_remove() connector: ffff8801ade43000 kdev: ffff8801a9419800
> [ 6824.572091] drm_connector_cleanup(ffff8801ade43000)::329 connector->registered: 0 cpu: 3
> [ 6824.572101] drm_connector_cleanup() kfree() connector->name: 'DP-6' &name: ffff8801ade43048
> [ 6824.572110] drm_dp_free_mst_branch_device() kfree mstb: ffff88030ac22600
> [ 6824.572117] drm_dp_free_mst_port() kfree port: ffff8801ade40800

Push button to switch back:

> [ 6837.349693] drm_connector_init() connector->name: 'DP-3' &name: ffff88040231d848
> [ 6837.349894] drm_sysfs_connector_add() connector: ffff88040231d800 kdev: ffff8801ae99f400
> [ 6837.352786] drm_connector_init() connector->name: 'DP-5' &name: ffff880402318048
> [ 6837.352951] drm_sysfs_connector_add() connector: ffff880402318000 kdev: ffff8801ae99c000
> [ 6837.353036] drm_connector_init() connector->name: 'DP-6' &name: ffff88040d37f048
> [ 6837.353154] drm_sysfs_connector_add() connector: ffff88040d37f000 kdev: ffff8801ae99ec00

I can type into the X session, but both screens are blank.  When I press
Ctrl-Alt-F2, I get:

> [ 6850.494310] drm_connector_cleanup(ffff8801ade47000)::329 connector->registered: 0 cpu: 1
> [ 6850.494314] drm_connector_cleanup() kfree() connector->name: 'DP-4' &name: ffff8801ade47048

Now I can switch back to X and everything is OK again.
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