linux-kernel - Re: [PATCH 1/2] Revert "drm/sched: fix timeout handling v2"

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Message-ID: <875zx7o82m.fsf@anholt.net>
Date:   Thu, 08 Nov 2018 08:19:45 -0800
From:   Eric Anholt <eric@...olt.net>
To:     "Koenig\, Christian" <Christian.Koenig@....com>,
        "dri-devel\@lists.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Cc:     "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        Nayan Deshmukh <nayan26deshmukh@...il.com>,
        "Deucher\, Alexander" <Alexander.Deucher@....com>
Subject: Re: [PATCH 1/2] Revert "drm/sched: fix timeout handling v2"

"Koenig, Christian" <Christian.Koenig@....com> writes:

> Am 08.11.18 um 17:04 schrieb Eric Anholt:
>> This reverts commit 0efd2d2f68cd5dbddf4ecd974c33133257d16a8e.  Fixes
>> this failure in V3D GPU reset:
>>
>> [ 1418.227796] Unable to handle kernel NULL pointer dereference at virtual address 00000018
>> [ 1418.235947] pgd = dc4c55ca
>> [ 1418.238695] [00000018] *pgd=80000040004003, *pmd=00000000
>> [ 1418.244132] Internal error: Oops: 206 [#1] SMP ARM
>> [ 1418.248934] Modules linked in:
>> [ 1418.252001] CPU: 0 PID: 10253 Comm: kworker/0:0 Not tainted 4.19.0-rc6+ #486
>> [ 1418.259058] Hardware name: Broadcom STB (Flattened Device Tree)
>> [ 1418.265002] Workqueue: events drm_sched_job_timedout
>> [ 1418.269986] PC is at dma_fence_remove_callback+0x8/0x50
>> [ 1418.275218] LR is at drm_sched_job_timedout+0x4c/0x118
>> ...
>> [ 1418.415891] [<c086b754>] (dma_fence_remove_callback) from [<c06e7e6c>] (drm_sched_job_timedout+0x4c/0x118)
>> [ 1418.425571] [<c06e7e6c>] (drm_sched_job_timedout) from [<c0242500>] (process_one_work+0x2c8/0x7bc)
>> [ 1418.434552] [<c0242500>] (process_one_work) from [<c0242a38>] (worker_thread+0x44/0x590)
>> [ 1418.442663] [<c0242a38>] (worker_thread) from [<c0249b10>] (kthread+0x160/0x168)
>> [ 1418.450076] [<c0249b10>] (kthread) from [<c02010ac>] (ret_from_fork+0x14/0x28)
>>
>> Cc: Christian König <christian.koenig@....com>
>> Cc: Nayan Deshmukh <nayan26deshmukh@...il.com>
>> Cc: Alex Deucher <alexander.deucher@....com>
>> Signed-off-by: Eric Anholt <eric@...olt.net>
>
> Well NAK. The problem here is that fence->parent is NULL which is most 
> likely caused by an issue somewhere else.
>
> We could easily work around that with an extra NULL check, but reverting 
> the patch would break GPU recovery again.

My GPU recovery works with the revert and reliably doesn't work without
it, so my idea of "break GPU recovery" is the opposite of yours.  Can
you help figure out what in this change broke my driver?

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