linux-kernel - Re: [PATCH 3/3] drm/amdgpu: Switch to interrupted wait to recover from ring hang.

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Date:   Tue, 24 Apr 2018 11:30:03 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     "Panariti\, David" <David.Panariti@....com>
Cc:     "Grodzovsky\, Andrey" <Andrey.Grodzovsky@....com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "amd-gfx\@lists.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "Deucher\, Alexander" <Alexander.Deucher@....com>,
        "Koenig\, Christian" <Christian.Koenig@....com>,
        "oleg\@redhat.com" <oleg@...hat.com>,
        "akpm\@linux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/3] drm/amdgpu: Switch to interrupted wait to recover from ring hang.

"Panariti, David" <David.Panariti@....com> writes:

> Andrey Grodzovsky <andrey.grodzovsky@....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.

Eric


>> If the ring is hanging for some reason allow to recover the waiting by sending fatal signal.
>>
>> Originally-by: David Panariti <David.Panariti@....com>
>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@....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;
>> +
>> +                     if (fatal_signal_pending(current)) {
>> +                             DRM_ERROR("Error (%ld) waiting for fence!\n", r);
>> +                             return r;
>> +                     }
>>               }
>>       }
>>
>> --
>> 2.7.4
>>
Eric