Re: [PATCH 09/19] drm/radeon: handle lockup in delayed work, v2

From: Christian KÃnig
Date: Mon Aug 04 2014 - 04:37:15 EST


Hi Maarten,

Sorry for the delay. I've got way to much todo recently.

Am 01.08.2014 um 19:46 schrieb Maarten Lankhorst:

On 01-08-14 18:35, Christian KÃnig wrote:
Am 31.07.2014 um 17:33 schrieb Maarten Lankhorst:
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
---
V1 had a nasty bug breaking gpu lockup recovery. The fix is not
allowing radeon_fence_driver_check_lockup to take exclusive_lock,
and kill it during lockup recovery instead.
That looks like the delayed work starts running as soon as we submit a fence, and not when it's needed for waiting.

Since it's a backup for failing IRQs I would rather put it into radeon_irq_kms.c and start/stop it when the IRQs are started/stoped.
The delayed work is not just for failing irq's, it's also the handler that's used to detect lockups, which is why I trigger after processing fences, and reset the timer after processing.

The idea was turning the delayed work on and off when we turn the irq on and off as well, processing of the delayed work handler can still happen in radeon_fence.c


Specifically what happened was this scenario:

- lock up occurs
- write lock taken by gpu_reset
- delayed work runs, tries to acquire read lock, blocks
- gpu_reset tries to cancel delayed work synchronously
- has to wait for delayed work to finish -> deadlock

Why do you want to disable the work item from the lockup handler in the first place?

Just take the exclusive lock in the work item, when it concurrently runs with the lockup handler it will just block for the lockup handler to complete.

Regards,
Christian.

~Maarten

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