[PATCH] drm/i915: Stop using flush_scheduled_work on driver remove

[Tvrtko Ursulin]

On 23/09/2022 17:16, Ville Syrjälä wrote:
> On Fri, Sep 23, 2022 at 03:29:34PM +0100, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>
>> Kernel is trying to eliminate callers of flush_scheduled_work so lets
>> try to accommodate.
>>
>> We currently call it from intel_modeset_driver_remove_noirq on the driver
>> remove path but the comment next to it does not tell me what exact work it
>> wants to flush.
>>
>> I can spot three (or four) works using the system_wq:
>>
>>    ..hotplug.reenable_work
>>    ..hotplug.hotplug_work
> 
> Looks like we at least try to shoot those down via
> intel_irq_uninstall()
>   ->intel_hpd_cancel_work()
>    ->cancel_delayed_work_sync()
> 
> But I'm not sure how broken the hpd disable path is here.
> I know hpd cancel vs. irq disable has some known ordering
> issues during suspend at least, some of which I think may
> have gotten fixed recently. But hpd cancel is still a bit
> of a mess in general.
> 
> Here we at least do cancel all the hpd works after irqs
> have been disabled, so I don't think any further flushing
> should help with whatever races we have left in there.
> 
>>    ..psr.dc3co_work
> 
> I think the whole dc3co thing should be disabled atm,
> so nothing should ever schedule this. We should
> probably garbage collect the whole thing...
> 
>>    ..crtc->drrs.work
> 
> That one should have been killed in
> intel_display_driver_unregister()
>   ->drm_atomic_helper_shutdown()
>    ->...
>     ->intel_drrs_deactivate()
>      ->cancel_delayed_work_sync()
> 
>> So if I replace it with intel_hpd_cancel_work() that appears would handle
>> the first two. What about the other two?
> 
> Other stuff that comes to mind is the pps vdd_off work.
> But looks like that should get taken down in the
> encoder->destroy() hook at the latest (via
> intel_mode_config_cleanup()).
> 
> psr.work at least has a cancel_work_sync() in intel_psr_disable(),
> so should hopefully get killed the same way as drrs.
> 
> opregion.asle_work seems to get cancelled from the unregister path.
> 
> The ones that look broken to me are dmc.work and fbc underrun_work.

Right, so I missed some and things are a bit more complicated. Okay to 
leave this with you, even if on a backlog?

Regards,

Tvrtko

> 
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>> Cc: Jani Nikula <jani.nikula at intel.com>
>> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
>> Cc: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
>> ---
>> I am clueless about the display paths and only send this because Jani
>> convinced me to send a patch to kick off the discussion. No expectations
>> whatsoever this is correct or complete.
>> ---
>>   drivers/gpu/drm/i915/display/intel_display.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
>> index 2d0018ae34b1..0eb72530a003 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display.c
>> +++ b/drivers/gpu/drm/i915/display/intel_display.c
>> @@ -8980,7 +8980,7 @@ void intel_modeset_driver_remove_noirq(struct drm_i915_private *i915)
>>   	intel_unregister_dsm_handler();
>>   
>>   	/* flush any delayed tasks or pending work */
>> -	flush_scheduled_work();
>> +	intel_hpd_cancel_work(i915);
>>   
>>   	intel_hdcp_component_fini(i915);
>>   
>> -- 
>> 2.34.1
>