[PATCH] drm/radeon: signal all fences after lockup to avoid endless waiting in GEM_WAIT

Marek Olšák maraeo at gmail.com
Sun Oct 13 22:16:55 CEST 2013 

This seems to be better. It can do about 3-5 resets correctly, then
the GPU resuming fails:

[  246.882780] [drm:cik_resume] *ERROR* cik startup failed on resume

and then the GPU is being reset again and again endlessly without success.

The dmesg of the endless resets is attached.

Marek

On Sun, Oct 13, 2013 at 2:47 PM, Christian König
<deathsimple at vodafone.de> wrote:
> I've figured out what was wrong with the patch. We need to reset the
> "needs_reset" flag earlier, otherwise the IB test might think we are in a
> lockup and aborts the reset after waiting for the minimum timeout period.
>
> Please try the attached patch instead.
>
> Thanks,
> Christian.
>
> Am 09.10.2013 14:04, schrieb Marek Olšák:
>
>> The ring test of the first compute ring always fails and it shouldn't
>> affect the GPU reset in any way.
>>
>> I can't tell if the deadlock issue is fixed, because the GPU reset
>> usually fails with your patch. It always succeeded without your patch.
>>
>> Marek
>>
>> On Wed, Oct 9, 2013 at 1:09 PM, Christian König <deathsimple at vodafone.de>
>> wrote:
>>>
>>> Mhm, that doesn't looks like anything related but more like the reset of
>>> the
>>> compute ring didn't worked.
>>>
>>> How often does that happen? And do you still get the problem where X
>>> waits
>>> for a fence that never comes back?
>>>
>>> Christian.
>>>
>>> Am 09.10.2013 12:36, schrieb Marek Olšák:
>>>
>>>> I'm afraid your patch sometimes causes the GPU reset to fail, which
>>>> had never happened before IIRC.
>>>>
>>>> The dmesg log from the failure is attached.
>>>>
>>>> Marek
>>>>
>>>> On Tue, Oct 8, 2013 at 6:21 PM, Christian König
>>>> <deathsimple at vodafone.de>
>>>> wrote:
>>>>>
>>>>> Hi Marek,
>>>>>
>>>>> please try the attached patch as a replacement for your signaling all
>>>>> fences
>>>>> patch. I'm not 100% sure if it fixes all issues, but it's at least a
>>>>> start.
>>>>>
>>>>> Thanks,
>>>>> Christian.
>>>>>
>>>>> Am 07.10.2013 13:08, schrieb Christian König:
>>>>>
>>>>>>> First of all, I can't complain about the reliability of the hardware
>>>>>>> GPU reset. It's mostly the kernel driver that happens to run into a
>>>>>>> deadlock at the same time.
>>>>>>
>>>>>>
>>>>>> Alex and I spend quite some time on making this reliable again after
>>>>>> activating more rings and adding VM support. The main problem is that
>>>>>> I
>>>>>> couldn't figure out where the CPU deadlock comes from, cause I
>>>>>> couldn't
>>>>>> reliable reproduce the issue.
>>>>>>
>>>>>> What is the content of /proc/<pid of X server>/task/*/stack and
>>>>>> sys/kernel/debug/dri/0/radeon_fence_info when the X server is stuck in
>>>>>> the
>>>>>> deadlock situation?
>>>>>>
>>>>>> I'm pretty sure that we nearly always have a problem when two threads
>>>>>> are
>>>>>> waiting for fences on one of them detects that we have a lockup while
>>>>>> the
>>>>>> other one keeps holding the exclusive lock. Signaling all fences might
>>>>>> work
>>>>>> around that problem, but it probably would be better to fix the
>>>>>> underlying
>>>>>> issue.
>>>>>>
>>>>>> Going to take a deeper look into it.
>>>>>>
>>>>>> Christian.
>>>>>>
>>>>>> Am 03.10.2013 02:45, schrieb Marek Olšák:
>>>>>>>
>>>>>>> First of all, I can't complain about the reliability of the hardware
>>>>>>> GPU reset. It's mostly the kernel driver that happens to run into a
>>>>>>> deadlock at the same time.
>>>>>>>
>>>>>>> Regarding the issue with fences, the problem is that the GPU reset
>>>>>>> completes successfully according to dmesg, but X doesn't respond. I
>>>>>>> can move the cursor on the screen, but I can't do anything else and
>>>>>>> the UI is frozen. gdb says that X is stuck in GEM_WAIT_IDLE. I can
>>>>>>> easily reproduce this, because it's the most common reason why a GPU
>>>>>>> lockup leads to frozen X. The GPU actually recovers, but X is hung. I
>>>>>>> can't tell whether the fences are just not signalled or whether there
>>>>>>> is actually a real CPU deadlock I can't see.
>>>>>>>
>>>>>>> This patch makes the problem go away and GPU resets are successful
>>>>>>> (except for extreme cases, see below). With a small enough lockup
>>>>>>> timeout, the lockups are just a minor annoyance and I thought I could
>>>>>>> get through a piglit run just with a few tens or hundreds of GPU
>>>>>>> resets...
>>>>>>>
>>>>>>> A different type of deadlock showed up, though it needs a lot of
>>>>>>> concurrently-running apps like piglit. What happened is that the
>>>>>>> kernel driver was stuck/deadlocked in radeon_cs_ioctl presumably due
>>>>>>> to a GPU hang while holding onto the exclusive lock, and another
>>>>>>> thread wanting to do the GPU reset was unable to acquire the lock.
>>>>>>>
>>>>>>> That said, I will use the patch locally, because it helps a lot. I
>>>>>>> got
>>>>>>> a few lockups while writing this email and I'm glad I didn't have to
>>>>>>> reboot.
>>>>>>>
>>>>>>> Marek
>>>>>>>
>>>>>>> On Wed, Oct 2, 2013 at 4:50 PM, Christian König
>>>>>>> <deathsimple at vodafone.de>
>>>>>>> wrote:
>>>>>>>>
>>>>>>>> Possible, but I would rather guess that this doesn't work because
>>>>>>>> the
>>>>>>>> IB
>>>>>>>> test runs into a deadlock situation and so the GPU reset never fully
>>>>>>>> completes.
>>>>>>>>
>>>>>>>> Can you reproduce the problem?
>>>>>>>>
>>>>>>>> If you want to make GPU resets more reliable I would rather suggest
>>>>>>>> to
>>>>>>>> remove the ring lock dependency.
>>>>>>>> Then we should try to give all the fence wait functions a (reliable)
>>>>>>>> timeout and move reset handling a layer up into the ioctl functions.
>>>>>>>> But for
>>>>>>>> this you need to rip out the old PM code first.
>>>>>>>>
>>>>>>>> Christian.
>>>>>>>>
>>>>>>>> Marek Olšák <maraeo at gmail.com> schrieb:
>>>>>>>>
>>>>>>>>> I'm afraid signalling the fences with an IB test is not reliable.
>>>>>>>>>
>>>>>>>>> Marek
>>>>>>>>>
>>>>>>>>> On Wed, Oct 2, 2013 at 3:52 PM, Christian König
>>>>>>>>> <deathsimple at vodafone.de> wrote:
>>>>>>>>>>
>>>>>>>>>> NAK, after recovering from a lockup the first thing we do is
>>>>>>>>>> signalling all remaining fences with an IB test.
>>>>>>>>>>
>>>>>>>>>> If we don't recover we indeed signal all fences manually.
>>>>>>>>>>
>>>>>>>>>> Signalling all fences regardless of the outcome of the reset
>>>>>>>>>> creates
>>>>>>>>>> problems with both types of partial resets.
>>>>>>>>>>
>>>>>>>>>> Christian.
>>>>>>>>>>
>>>>>>>>>> Marek Olšák <maraeo at gmail.com> schrieb:
>>>>>>>>>>
>>>>>>>>>>> From: Marek Olšák <marek.olsak at amd.com>
>>>>>>>>>>>
>>>>>>>>>>> After a lockup, fences are not signalled sometimes, causing
>>>>>>>>>>> the GEM_WAIT_IDLE ioctl to never return, which sometimes results
>>>>>>>>>>> in an X server freeze.
>>>>>>>>>>>
>>>>>>>>>>> This fixes only one of many deadlocks which can occur during a
>>>>>>>>>>> lockup.
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Marek Olšák <marek.olsak at amd.com>
>>>>>>>>>>> ---
>>>>>>>>>>> drivers/gpu/drm/radeon/radeon_device.c | 5 +++++
>>>>>>>>>>> 1 file changed, 5 insertions(+)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/drivers/gpu/drm/radeon/radeon_device.c
>>>>>>>>>>> b/drivers/gpu/drm/radeon/radeon_device.c
>>>>>>>>>>> index 841d0e0..7b97baa 100644
>>>>>>>>>>> --- a/drivers/gpu/drm/radeon/radeon_device.c
>>>>>>>>>>> +++ b/drivers/gpu/drm/radeon/radeon_device.c
>>>>>>>>>>> @@ -1552,6 +1552,11 @@ int radeon_gpu_reset(struct radeon_device
>>>>>>>>>>> *rdev)
>>>>>>>>>>>          radeon_save_bios_scratch_regs(rdev);
>>>>>>>>>>>          /* block TTM */
>>>>>>>>>>>          resched =
>>>>>>>>>>> ttm_bo_lock_delayed_workqueue(&rdev->mman.bdev);
>>>>>>>>>>> +
>>>>>>>>>>> +      mutex_lock(&rdev->ring_lock);
>>>>>>>>>>> +      radeon_fence_driver_force_completion(rdev);
>>>>>>>>>>> +      mutex_unlock(&rdev->ring_lock);
>>>>>>>>>>> +
>>>>>>>>>>>          radeon_pm_suspend(rdev);
>>>>>>>>>>>          radeon_suspend(rdev);
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> 1.8.1.2
>>>>>>>>>>>
>>>>>>>>>>> _______________________________________________
>>>>>>>>>>> dri-devel mailing list
>>>>>>>>>>> dri-devel at lists.freedesktop.org
>>>>>>>>>>> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> dri-devel mailing list
>>>>>> dri-devel at lists.freedesktop.org
>>>>>> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>>>>>
>>>>>
>
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