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

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Message-ID: <53DBD269.80807@canonical.com>
Date:	Fri, 01 Aug 2014 19:46:17 +0200
From:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
To:	Christian König <christian.koenig@....com>,
	airlied@...ux.ie
CC:	thellstrom@...are.com, nouveau@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	bskeggs@...hat.com, alexander.deucher@....com
Subject: Re: [PATCH 09/19] drm/radeon: handle lockup in delayed work, v2



On 01-08-14 18:35, Christian König wrote:
> Am 31.07.2014 um 17:33 schrieb Maarten Lankhorst:
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@...onical.com>
>> ---
>> 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.

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

~Maarten
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