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SubjectRe: drm_sched with panfrost crash on T820
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Hi Andrey,

On 27/09/2019 22:55, Grodzovsky, Andrey wrote:
> Can you please use addr2line or gdb to pinpoint where in
> drm_sched_increase_karma you hit the NULL ptr ? It looks like the guilty
> job, but to be sure.

Did a new run from 5.3:

[ 35.971972] Call trace:
[ 35.974391] drm_sched_increase_karma+0x5c/0xf0 ffff000010667f38 FFFF000010667F94 drivers/gpu/drm/scheduler/sched_main.c:335


The crashing line is :
if (bad->s_fence->scheduled.context ==
entity->fence_context) {

Doesn't seem related to guilty job.

Neil

>
> Andrey
>
> On 9/27/19 4:12 AM, Neil Armstrong wrote:
>> Hi Christian,
>>
>> In v5.3, running dEQP triggers the following kernel crash :
>>
>> [ 20.224982] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000038
>> [...]
>> [ 20.291064] Hardware name: Khadas VIM2 (DT)
>> [ 20.295217] Workqueue: events drm_sched_job_timedout
>> [...]
>> [ 20.304867] pc : drm_sched_increase_karma+0x5c/0xf0
>> [ 20.309696] lr : drm_sched_increase_karma+0x44/0xf0
>> [...]
>> [ 20.396720] Call trace:
>> [ 20.399138] drm_sched_increase_karma+0x5c/0xf0
>> [ 20.403623] panfrost_job_timedout+0x12c/0x1e0
>> [ 20.408021] drm_sched_job_timedout+0x48/0xa0
>> [ 20.412336] process_one_work+0x1e0/0x320
>> [ 20.416300] worker_thread+0x40/0x450
>> [ 20.419924] kthread+0x124/0x128
>> [ 20.423116] ret_from_fork+0x10/0x18
>> [ 20.426653] Code: f9400001 540001c0 f9400a83 f9402402 (f9401c64)
>> [ 20.432690] ---[ end trace bd02f890139096a7 ]---
>>
>> Which never happens, at all, on v5.2.
>>
>> I did a (very) long (7 days, ~100runs) bisect run using our LAVA lab (thanks tomeu !), but
>> bisecting was not easy since the bad commit landed on drm-misc-next after v5.1-rc6, and
>> then v5.2-rc1 was backmerged into drm-misc-next at:
>> [1] 374ed5429346 Merge drm/drm-next into drm-misc-next
>>
>> Thus bisecting between [1] ang v5.2-rc1 leads to commit based on v5.2-rc1... where panfrost was
>> not enabled in the Khadas VIM2 DT.
>>
>> Anyway, I managed to identify 3 possibly breaking commits :
>> [2] 290764af7e36 drm/sched: Keep s_fence->parent pointer
>> [3] 5918045c4ed4 drm/scheduler: rework job destruction
>> [4] a5343b8a2ca5 drm/scheduler: Add flag to hint the release of guilty job.
>>
>> But [1] and [2] doesn't crash the same way :
>> [ 16.257912] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000060
>> [...]
>> [ 16.308307] CPU: 4 PID: 80 Comm: kworker/4:1 Not tainted 5.1.0-rc2-01185-g290764af7e36-dirty #378
>> [ 16.317099] Hardware name: Khadas VIM2 (DT)
>> [...])
>> [ 16.330907] pc : refcount_sub_and_test_checked+0x4/0xb0
>> [ 16.336078] lr : refcount_dec_and_test_checked+0x14/0x20
>> [...]
>> [ 16.423533] Process kworker/4:1 (pid: 80, stack limit = 0x(____ptrval____))
>> [ 16.430431] Call trace:
>> [ 16.432851] refcount_sub_and_test_checked+0x4/0xb0
>> [ 16.437681] drm_sched_job_cleanup+0x24/0x58
>> [ 16.441908] panfrost_job_free+0x14/0x28
>> [ 16.445787] drm_sched_job_timedout+0x6c/0xa0
>> [ 16.450102] process_one_work+0x1e0/0x320
>> [ 16.454067] worker_thread+0x40/0x450
>> [ 16.457690] kthread+0x124/0x128
>> [ 16.460882] ret_from_fork+0x10/0x18
>> [ 16.464421] Code: 52800000 d65f03c0 d503201f aa0103e3 (b9400021)
>> [ 16.470456] ---[ end trace 39a67412ee1b64b5 ]---
>>
>> and [3] fails like on v5.3 (in drm_sched_increase_karma):
>> [ 33.830080] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000038
>> [...]
>> [ 33.871946] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>> [ 33.877450] Modules linked in:
>> [ 33.880474] CPU: 6 PID: 81 Comm: kworker/6:1 Not tainted 5.1.0-rc2-01186-ga5343b8a2ca5-dirty #380
>> [ 33.889265] Hardware name: Khadas VIM2 (DT)
>> [ 33.893419] Workqueue: events drm_sched_job_timedout
>> [...]
>> [ 33.903069] pc : drm_sched_increase_karma+0x5c/0xf0
>> [ 33.907898] lr : drm_sched_increase_karma+0x44/0xf0
>> [...]
>> [ 33.994924] Process kworker/6:1 (pid: 81, stack limit = 0x(____ptrval____))
>> [ 34.001822] Call trace:
>> [ 34.004242] drm_sched_increase_karma+0x5c/0xf0
>> [ 34.008726] panfrost_job_timedout+0x12c/0x1e0
>> [ 34.013122] drm_sched_job_timedout+0x48/0xa0
>> [ 34.017438] process_one_work+0x1e0/0x320
>> [ 34.021402] worker_thread+0x40/0x450
>> [ 34.025026] kthread+0x124/0x128
>> [ 34.028218] ret_from_fork+0x10/0x18
>> [ 34.031755] Code: f9400001 540001c0 f9400a83 f9402402 (f9401c64)
>> [ 34.037792] ---[ end trace be3fd6f77f4df267 ]---
>>
>>
>> When I revert [3] on [1], i get the same crash as [2], meaning
>> the commit [3] masks the failure [2] introduced.
>>
>> Do you know how to solve this ?
>>
>> Thanks,
>> Neil

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