drm/lima: mask irqs in timeout path before hard reset

In the Linux kernel, the following vulnerability has been resolved:

drm/lima: mask irqs in timeout path before hard reset

There is a race condition in which a rendering job might take just long

enough to trigger the drm sched job timeout handler but also still

complete before the hard reset is done by the timeout handler.

This runs into race conditions not expected by the timeout handler.

In some very specific cases it currently may result in a refcount

imbalance on lima_pm_idle, with a stack dump such as:

[10136.669170] WARNING: CPU: 0 PID: 0 at drivers/gpu/drm/lima/lima_devfreq.c:205 lima_devfreq_record_idle+0xa0/0xb0

...

[10136.669459] pc : lima_devfreq_record_idle+0xa0/0xb0

...

[10136.669628] Call trace:

[10136.669634] lima_devfreq_record_idle+0xa0/0xb0

[10136.669646] lima_sched_pipe_task_done+0x5c/0xb0

[10136.669656] lima_gp_irq_handler+0xa8/0x120

[10136.669666] __handle_irq_event_percpu+0x48/0x160

[10136.669679] handle_irq_event+0x4c/0xc0

We can prevent that race condition entirely by masking the irqs at the

beginning of the timeout handler, at which point we give up on waiting

for that job entirely.

The irqs will be enabled again at the next hard reset which is already

done as a recovery by the timeout handler.