Re: drm_sched with panfrost crash on T820

[Neil Armstrong <narmstrong@baylibre.com>]

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