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

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Message-ID: <38047e61-6859-14dc-956d-036b26e984e7@amd.com>
Date:   Tue, 24 Apr 2018 12:38:50 -0400
From:   Andrey Grodzovsky <Andrey.Grodzovsky@....com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        Alexander.Deucher@....com, Christian.Koenig@....com,
        David.Panariti@....com, oleg@...hat.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 3/3] drm/amdgpu: Switch to interrupted wait to recover
 from ring hang.



On 04/24/2018 12:14 PM, Eric W. Biederman wrote:
> Andrey Grodzovsky <andrey.grodzovsky@....com> writes:
>
>> 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;
>> +			}
> It looks like if you make this code say:
> 			if (fatal_signal_pending(current) ||
> 			    (current->flags & PF_EXITING)) {
> 				DRM_ERROR("Error (%ld) waiting for fence!\n", r);
> 				return r;
>>   		}
>>   	}
> Than you would not need the horrible hack want_signal to deliver signals
> to processes who have passed exit_signal() and don't expect to need
> their signal handling mechanisms anymore.

Let me clarify,  the change in want_signal wasn't addressing this code 
but hang in
drm_sched_entity_do_release->wait_event_killable, when you try to 
gracefully terminate by waiting
for all job completions on the GPU pipe you process is using.

Andrey

>
> Eric
>