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SubjectRe: [PATCH 3/3] drm/amdgpu: Switch to interrupted wait to recover from ring hang.
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On 04/24/2018 12:30 PM, Eric W. Biederman wrote:
> "Panariti, David" <David.Panariti@amd.com> writes:
>
>> Andrey Grodzovsky <andrey.grodzovsky@amd.com> writes:
>>> Kind of dma_fence_wait_killable, except that we don't have such API
>>> (maybe worth adding ?)
>> Depends on how many places it would be called, or think it might be called. Can always factor on the 2nd time it's needed.
>> Factoring, IMO, rarely hurts. The factored function can easily be visited using `M-.' ;->
>>
>> Also, if the wait could be very long, would a log message, something like "xxx has run for Y seconds." help?
>> I personally hate hanging w/no info.
> Ugh. This loop appears susceptible to loosing wake ups. There are
> races between when a wake-up happens, when we clear the sleeping state,
> and when we test the stat to see if we should stat awake. So yes
> implementing a dma_fence_wait_killable that handles of all that
> correctly sounds like an very good idea.

I am not clear here - could you be more specific about what races will
happen here, more bellow
>
> Eric
>
>
>>> If the ring is hanging for some reason allow to recover the waiting by sending fatal signal.
>>>
>>> Originally-by: David Panariti <David.Panariti@amd.com>
>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
>>> ---
>>> drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c | 14 ++++++++++----
>>> 1 file changed, 10 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
>>> index eb80edf..37a36af 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
>>> @@ -421,10 +421,16 @@ int amdgpu_ctx_wait_prev_fence(struct amdgpu_ctx *ctx, unsigned ring_id)
>>>
>>> if (other) {
>>> signed long r;
>>> - r = dma_fence_wait_timeout(other, false, MAX_SCHEDULE_TIMEOUT);
>>> - if (r < 0) {
>>> - DRM_ERROR("Error (%ld) waiting for fence!\n", r);
>>> - return r;
>>> +
>>> + while (true) {
>>> + if ((r = dma_fence_wait_timeout(other, true,
>>> + MAX_SCHEDULE_TIMEOUT)) >= 0)
>>> + return 0;
>>> +

Do you mean that by the time I reach here some other thread from my
group already might dequeued SIGKILL since it's a shared signal and
hence fatal_signal_pending will return false ? Or are you talking about
the dma_fence_wait_timeout implementation in dma_fence_default_wait with
schedule_timeout ?

Andrey

>>> + if (fatal_signal_pending(current)) {
>>> + DRM_ERROR("Error (%ld) waiting for fence!\n", r);
>>> + return r;
>>> + }
>>> }
>>> }
>>>
>>> --
>>> 2.7.4
>>>
> Eric

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