Re: [PATCH 3/3] drm/amdgpu: Fix multi-level page table bugs for large BOs

From: "Michel Dänzer" <michel-otUistvHUpPR7s880joybQ@public.gmane.org>
To: "Felix Kuehling" <felix.kuehling-5C7GfCeVMHo@public.gmane.org>,
	"Christian König"
	<deathsimple-ANTagKRnAhcb1SvskN2V4Q@public.gmane.org>,
	"Zhang,
	Jerry (Junwei)" <Jerry.Zhang-5C7GfCeVMHo@public.gmane.org>,
	"Koenig,
	Christian" <Christian.Koenig-5C7GfCeVMHo@public.gmane.org>,
	"Zhou,
	David(ChunMing)" <David1.Zhou-5C7GfCeVMHo@public.gmane.org>
Cc: "Deucher,
	Alexander" <Alexander.Deucher-5C7GfCeVMHo@public.gmane.org>,
	"Russell, Kent" <Kent.Russell-5C7GfCeVMHo@public.gmane.org>,
	"amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org"
	<amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org>
Subject: Re: [PATCH 3/3] drm/amdgpu: Fix multi-level page table bugs for large BOs
Date: Wed, 29 Mar 2017 23:46:27 +0900	[thread overview]
Message-ID: <a2d6c20e-d35f-e135-342b-47f86683c3e3@daenzer.net> (raw)
In-Reply-To: <bdbacee3-2c61-ebcb-1421-5c0a77dc27e0-5C7GfCeVMHo@public.gmane.org>

On 29/03/17 11:32 PM, Felix Kuehling wrote:
> On 17-03-29 02:52 AM, Christian König wrote:
>>
>> Please clean that up and also remove all those WARN_ON(), we don't
>> want to spam the system log with backtraces like this.
> 
> I disagree. When you see the backtraces from WARN_ONs in
> amdgpu_vm_get_pt, it means the driver is trying to update a page table
> that hasn't been allocated. Without those WARN_ONs there is absolutely
> no warning of any kind - amdgpu_vm_update_pte just fails silently (it's
> a void function).
> 
> Therefore I wouldn't call those warnings spam. Given that the VM PT
> allocation code for multi-levels is non-trivial, I think that's a good
> sanity check to have and really helpful to see in a log when user report
> random VM faults.

WARN_ON_ONCE might be a compromise. We'll still get a backtrace, but it
won't cause crazy log spam if the bad condition is consistently hit.

-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer
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